nitroarginine and Hypertension

Many studies indicate that renal haemodynamic function in angiotensin II- (ANG II) dependent hypertension is not reduced as much as would be predicted from the elevated ANG II levels suggesting that counteracting renoprotective mechanisms are activated. One important renoprotective effect is mediated by increased levels of nitric oxide. Recent studies using the ANG II-infused hypertensive rat model have shown that inhibition of nitric oxide synthesis (NOS) causes greater decreases in renal blood flow and glomerular filtration rate in ANG II-infused hypertensive rats than in control rats. This augmented nitric oxide-dependent influence is localized primarily in the cortex and to the preglomerular vasculature. The differential effects on the renal cortex and medulla are also reflected by the differences in NOS activities and protein expression. Ca2+-dependent NOS activity was significantly greater in the cortex but not the medulla of the ANG II-infused hypertensive rats compared with control rats. This was associated with marked activation of endothelial NOS protein levels and smaller increases in neuronal NOS protein levels in the cortex but not in the medulla. In contrast, the Ca2+-independent NOS activity and the inducible NOS protein levels in the cortex were significantly lower in the ANG II-infused hypertensive rats. These data support the hypothesis that cortical Ca2+-dependent NOS, primarily endothelial NOS, is stimulated during the early phases of ANG II-induced hypertension and exerts a renoprotective effect on cortical haemodynamics.

Topics: Angiotensin II; Animals; Arterioles; Enzyme Inhibitors; Hypertension; Isoenzymes; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Renal Circulation

It has been proposed that flow-mediated shear stress regulates vascular tone; however, whether this operates in the human microcirculation is unknown. This study was designed to investigate the effect of shear stress on human microvascular tone, to assess the contribution of nitric oxide (NO), and to determine whether this mechanism is defective in hypertension and in hypercholesterolemia.. In 9 normal controls (NC), 11 hypertensive patients (HT), and 12 hypercholesterolemic patients (HChol), arteries (internal diameter 201+/-26 microm) isolated from gluteal fat biopsies were cannulated and perfused in chambers. Shear stress was induced by increasing the flow rate from 1 to 50 microL/min after preconstriction with norepinephrine (NE). Arterial internal diameter was expressed as percent of NE-induced constriction. In NC, shear stress induced flow-dependent vasodilation from 23+/-9% at 1 microL/min to 53+/-14% at 50 microL/min (P<0.0001), which was abolished by endothelial removal. The NO synthase inhibitor Nomega-nitro-L-arginine (L-NNA) significantly blunted this response (mean vasodilation decreased from 27+/-6% to 6+/-9%; P=0.04). HT had significant impairment of flow-mediated dilation (mean vasodilation 5+/-6%; P=0.01 versus NC), which was not affected by L-NNA. HChol had preserved flow-mediated vasodilation (mean vasodilation 24+/-7%; P=0.56 versus NC), but this was not significantly modified by L-NNA.. In the human microvasculature, shear stress induces endothelium-dependent, NO-mediated vasodilation. This phenomenon is blunted in HT patients because of reduced activity of NO. In contrast, the HChol microvasculature has preserved shear stress-induced dilation despite diminished NO activity.

Topics: Analysis of Variance; Biopsy; Endothelium, Vascular; Female; Humans; Hypercholesterolemia; Hypertension; Male; Microcirculation; Middle Aged; Muscle Tonus; Nitric Oxide; Nitric Oxide Synthase; Nitric Oxide Synthase Type III; Nitroarginine; Nitroprusside; Stress, Mechanical; Vasodilation

Sodium thiosulfate, a reversible oxidation product of hydrogen sulfide, has vasodilating and anti-oxidative properties, making it an attractive agent to alleviate damaging effects of hypertension. In experimental settings, inhibition of nitric oxide synthase causes hypertension, renal dysfunction and damage. We hypothesized that thiosulfate would attenuate renal injury and improve renal function, hemodynamics and the efficiency of oxygen utilization for sodium reabsorption in hypertensive renal disease. Additionally, thiosulfate co-administration would further improve these variables when compared to inhibiting the renin-angiotensin system alone. Nitric oxide synthase was inhibited in Sprague Dawley rats by administering N-ω-nitro-L-arginine (L-NNA) in the food for three weeks. After one week, rats were split into two groups; without and with thiosulfate in the drinking water. In a parallel study, rats given N-ω-nitro-L-arginine and the angiotensin converting enzyme inhibitor lisinopril at a relatively low dose in their food were divided into two groups; without and with thiosulfate in the drinking water. Treatment with thiosulfate alleviated hypertension (mean 190 vs. 229 mmHg), lowered plasma urea (mean 11.3 vs. 20.0 mmol/L) and improved the terminal glomerular filtration rate (mean 503 vs. 260 μl/min/100 gbw), effective renal plasma flow (mean 919 vs. 514 μl/min/100 gbw) and oxygen utilization for sodium reabsorption (mean 14.3 vs. 8.6 μmol/μmol). Combining thiosulfate with lisinopril further lowered renal vascular resistance (mean 43 vs. 63 mmHg/ml/min/100 gbw) and prevented glomerulosclerosis. Thus, our results suggest that thiosulfate has therapeutic potential in hypertensive renal disease and might be of value when added to standard antihypertensive therapies.

Topics: Animals; Blood Pressure; Enzyme Inhibitors; Hypertension; Kidney; NG-Nitroarginine Methyl Ester; Nitric Oxide; Nitroarginine; Rats; Rats, Sprague-Dawley; Thiosulfates

Plant-derived oleanolic acid (OA) and its related synthetic derivatives (Br-OA and Me-OA) possess antihypertensive effects in experimental animals. The present study investigated possible underlying mechanisms in rat isolated single ventricular myocytes and in vascular smooth muscles superfused at 37°C.. Cell shortening was assessed at 1 Hz using a video-based edge-detection system and the L-type Ca2+ current (ICaL) was measured using the whole-cell patch-clamp technique in single ventricular myocytes. Isometric tension was measured using force transducer in isolated aortic rings and in mesenteric arteries. Vascular effects were measured in endothelium-intact and denuded vessels in the presence of various enzyme or channel inhibitors.. OA and its derivatives increased cell shortening in cardiomyocytes isolated from normotensive rats but had no effect in those isolated from hypertensive animals. These triterpenes also caused relaxation in aortic rings and in mesenteric arteries pre-contracted with either phenylephrine or KCl-enriched solution. The relaxation was only partially inhibited by endothelium denudation, and also partly inhibited by the cyclooxygenase (COX) inhibitor indomethacin, with no additional inhibitory effect of the NO synthase inhibitor, N-ω-Nitro-L-arginine. A combination of both ATP-dependent channel inhibition by glibenclaminde and voltage-dependent K+ channel inhibition by 4-aminopyridine was necessary to fully inhibit the relaxation.. These data indicate that the effects of OA and its derivatives are mediated via both endothelium-dependent and independent mechanisms suggesting the involvement of COX in the endothelium-dependent effects and of vascular muscle K+ channels in the endothelium-independent effects. Finally, our results support the view that the antihypertensive action of OA and its derivatives is due to a decrease of vascular resistance with no negative inotropic effect on the heart.

Topics: Animals; Antihypertensive Agents; Endothelium, Vascular; Hypertension; Hypotension; Indomethacin; Male; Muscle Cells; Muscle, Smooth, Vascular; Nitroarginine; Oleanolic Acid; Phenylephrine; Potassium Channels; Potassium Chloride; Prostaglandin-Endoperoxide Synthases; Rats; Rats, Inbred Dahl; Rats, Wistar

We investigated the relationship between noradrenaline (NAd)-induced contractions, endothelial function, and hypertension in femoral arteries isolated from spontaneously hypertensive rats (SHR). In the femoral arteries of SHR, vs. age-matched control Wistar Kyoto (WKY) rats, contractions induced by NAd were increased. These effects were enhanced by endothelial denudation, which abolished the differences between the two groups. NAd-induced contractions were enhanced by nitric oxide (NO) synthase inhibition, and further increased by the blockade of endothelium-derived hyperpolarizing factor (EDHF). Conversely, NAd-induced contractions were inhibited by cyclooxygenase (COX) inhibition. In addition, in SHR arteries, acetylcholine-induced relaxation was reduced, and components of endothelium-derived factors were altered, such as increased COX-derived vasoconstrictor prostanoids, reduced EDHF, and preserved NO-mediated relaxation. In the femoral arteries of SHR, the production of prostanoids [6-keto prostaglandin (PG)F1α (a metabolite of prostacyclin (PGI2), PGE2, and PGF2α] and COX-2 protein were increased compared with that in WKY rats. By contrast, contractions induced by beraprost (a stable PGI2 analogue), PGE2, and U46619 (thromboxane/prostanoid receptor agonist) were similar between the SHR and WKY groups. Thus, NAd-induced femoral arterial contractions are augmented in SHR resulting from endothelial dysfunction and increased COX-derived vasoconstrictor prostanoid levels.

Topics: Acetylcholine; Animals; Biological Factors; Cyclooxygenase Inhibitors; Endothelium, Vascular; Femoral Artery; Hypertension; Male; Nitric Oxide Synthase; Nitroarginine; Norepinephrine; Prostaglandins; Rats, Inbred SHR; Rats, Inbred WKY; Vasoconstriction; Vasoconstrictor Agents

Alkaloids from Ba lotus seeds (ABLS) are a kind of important functional compounds in lotus seeds. The present study was designed to determine its hypertension prophylactic effects in the L-NNA-induced mouse hypertension model. The mice were treated with ABLS, the serum and tissues levels of NO, MDA, ET-1, VEGF, and CGRP were determined using the experimental kits, the mRNA levels of various genes in the heart muscle and blood vessel tissues were further determined by RT-PCR assay. ABLS could reduce the systolic blood pressure (SBP), mean blood pressure (MBP), and diastolic blood pressure (DBP), compared to that of the model control group. After ABLS treatment, the NO (nitric oxide) contents in serum, heart, liver, kidney and stomach of the mice were higher than that of the control mice, but the MDA (malonaldehyde) contents were lower than that of the control mice. The serum levels of ET-1 (endothelin-1), VEGF (vascular endothelial growth factor) were decreased after ABLS treatment, but CGRP (calcium gene related peptide) level was increased. The ABLS treated mice had higher mRNA expressions of HO-1, nNOS, and eNOS and lower expressions of ADM, RAMP2, IL-1β, TNF-α, and iNOS than the control mice. Higher concentration of ABLS had greater prophylactic effects, which were close to that of the hypertension drug captopril. These results indicated the hypertension prophylactic effects of ABLS could be further explored as novel medicine or functional food in the future.

Topics: Alkaloids; Animals; Blood Pressure; Disease Models, Animal; Humans; Hypertension; Interleukin-1beta; Male; Mice; Mice, Inbred ICR; Nitroarginine; Nymphaeaceae; Seeds; Tumor Necrosis Factor-alpha; Vascular Endothelial Growth Factor A

Whether NO, carbon monoxide (CO) and hydrogen sulfide (H2 S) compensate for each other when one or more is depleted is unclear. Inhibiting NOS causes hypertension and kidney injury. Both global depletion of H2 S by cystathionine γ-lyase (CSE) gene deletion and low levels of exogenous H2 S cause hypertension. Inhibiting CO-producing enzyme haeme oxygenase-1 (HO-1) makes rodents hypersensitive to hypertensive stimuli. We hypothesized that combined inhibition of NOS and HO-1 exacerbates hypertension and renal injury, but how combined inhibition of NOS and CSE affect hypertension and renal injury was unclear.. Rats were treated with inhibitors of NOS (L-nitroarginine; LNNA), CSE (DL-propargylglycine; PAG), or HO-1 (tin protoporphyrin; SnPP) singly for 1 or 4 weeks or in combinations for 4 weeks.. LNNA always reduced NO, decreased H2 S and increased CO after 4 weeks. PAG abolished H2 S, always enhanced CO and reduced NO, but not when used in combination with other inhibitors. SnPP always increased NO, enhanced H2 S and inhibited CO after 1 week. Rats treated with LNNA, but not PAG and SnPP, rapidly developed hypertension followed by renal dysfunction. LNNA-induced hypertension was ameliorated and renal dysfunction prevented by all additional treatments. Renal HO-1 expression was increased by LNNA in injured tubules and increased in all tubules by all other treatments.. The amelioration of LNNA-induced hypertension and renal injury by additional inhibition of H2 S and/or CO-producing enzymes appeared to be associated with secondary increases in renal CO or NO production.

Topics: Alkynes; Animals; Carbon Monoxide; Cystathionine gamma-Lyase; Glycine; Heme Oxygenase-1; Hydrogen Sulfide; Hypertension; Kidney; Male; Metalloporphyrins; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Protoporphyrins; Rats; Rats, Sprague-Dawley

Endothelial dysfunction is closely associated with hypertension. Protection of vascular endothelial cell is the key to prevention and treatment of hypertension. Uncaria rhynchophylla total alkaloids and Semen Raphani soluble alkaloid, isolated from traditional Chinese medicine Uncaria rbyncbopbylla and Semen Raphani respectively, exhibit properties of anti-hypertension and protection of blood vessels. In the present study, we observed the protective effect of the combined use of Uncaria rhynchophylla total alkaloids and Semen Raphani soluble alkaloid to the vascular endothelial cell in N'-nitro-L-arginine-induced hypertensive rats and investigate the preliminary mechanism. Blood pressure was detected by non-invasive rats tail method to observe the anti-hypertension effect of drugs. Scanning electron microscopy was used to observe the integrity or shedding state of vascular endothelial cell. The amount of circulating endothelial cells and CD54 and CD62P expression on circulating endothelial cells were tested to evaluate the endothelium function. In this study, we found that the Uncaria rhynchophylla total alkaloids and Semen Raphani soluble alkaloid compatibility can effectively lower the blood pressure, improve the structural integrity of vascular endothelium, and significantly reduce the number of circulating endothelial cells. Furthermore, the mean fluorescence intensity of CD54 and CD62P expressed showed decrease after the intervention of Uncaria rhynchophylla total alkaloids and Semen Raphani soluble alkaloid compatibility. In conclusion, the combination of effective components of the Uncaria rhynchophylla total alkaloids and Semen Raphani soluble alkaloid demonstrated good antihypertension effect and vascular endothelium protective effect. The preliminary mechanism of the protective effect may attribute to relieve the overall low-grade inflammation.

Topics: Animals; Antigens, CD; Blood Pressure; Brassicaceae; Cell Count; Cell Shape; Cytoprotection; Endothelial Cells; Hypertension; Male; Nitroarginine; Phytotherapy; Protective Agents; Rats, Inbred WKY; Uncaria

The leaves of Taxus chinensis var. mairei (Taxaceae) is used traditionally to fill pillows in some rural areas of China. Its volatile substances have been speculated to be capable of improving sleep quality, making blood pressure stable, and having diuretic capacity as recorded in Ancient Chinese Materia Medica. Using animal models and new technologies, we confirmed the hypotensive potential of volatile components from leaves of Taxus chinensis var. mairei (VCLT).. VCLT was obtained by supercritical CO(2) extraction equipment from Taxus chinensis var. mairei fresh leaves. Hypertensive rats were pre-induced by intraperitoneal (i,p.) injection of Nω-Nitro-l-Ariginine (l-NNA) for 15 days (15mg/kg, twice a day), then divided into 5 groups and subjected to the following treatments. l-NNA group (group 1) receiving l-NNA alone (15mg/kg, i.p., twice per day for 6 weeks); in addition to receiving l-NNA same as group 1, Hydrochlorothiazide (HDZ) group (group 2) receiving HDZ (orally administration, 5mg/kg, once per day for 6 weeks); VCLT groups (groups 3-5), including VCLT1, VCLT2, VCLT3. The VCLT rats were housed in an enclosed cage (2 rats/0.064m(3)). VCLT was mixed well and sprayed on fresh leaves surface of Taxus chinensis var. mairei (100ml/kg) with three dosages: 167g/kg (VCLT1), 233g/kg (VCLT2) and 333g/kg (VCLT3), respectively. Systolic Blood Pressure (SBP), plasma nitric oxide (NO), plasma angiotensin II, postprandial blood glucose, fasting blood glucose and blood lipids were determined.. VCLT prevented the increase of SBP and plasma angiotensin II in l-NNA treated rats. Although VCLT does not significantly reduce blood triglycerides (TG), high-density lipoprotein cholesterol (HDL-C) and low density lipoprotein cholesterol (LDL-C), it decreases total cholesterol (TC) while increasing plasma NO levels in a dose-dependent manner.. VCLT can be used as a natural and supplementary reagents for the treatment of hypertension.

Topics: Administration, Oral; Angiotensin II; Animals; Antihypertensive Agents; Biomarkers; Blood Glucose; Blood Pressure; Chromatography, Supercritical Fluid; Disease Models, Animal; Dose-Response Relationship, Drug; Drugs, Chinese Herbal; Hydrochlorothiazide; Hypertension; Lipids; Male; Nitric Oxide; Nitroarginine; Phytotherapy; Plant Leaves; Plants, Medicinal; Rats; Rats, Sprague-Dawley; Taxus; Time Factors; Volatilization

It has been reported that endothelin-1 (ET-1) overproduction and reduced nitric oxide (NO) production are closely related to the progression of renal diseases. In the present study, we examined the interrelation between ET-1 and NO system using rats treated with the combination of deoxycorticosterone acetate (DOCA)-salt and a non selective NO synthase inhibitor N(ω)-nitro-L-arginine (NOARG).. Rats were treated with DOCA-salt (15 mg/kg, plus drinking water containing 1% NaCl) for two weeks, and then additional treatment of NOARG (0.6 mg/ml in the drinking water) was performed for three days.. Combined treatment of DOCA-salt and NOARG drastically developed the severe renal dysfunction and tissue injury. This treatment additionally enhanced renal ET-1 production compared to the rats treated with DOCA-salt alone, whereas a selective ET(A) receptor antagonist ABT-627 completely prevented renal dysfunction and tissue injury. On the other hand, combined treatment of DOCA-salt and NOARG induced the phosphorylation of inhibitory protein kappa B (IκB), followed by the activation of nuclear factor-kappa B (NF-κB) in the kidney. In addition, pyrrolidine-dithiocarbamate completely suppressed not only NF-κB activation but also renal dysfunction and ET-1 overproduction.. These results suggest that NF-κB/ET-1/ET(A) receptor-mediated actions are responsible for the increased susceptibility to DOCA-salt induced renal injuries in the case of reduced NO production.

Topics: Animals; Atrasentan; Desoxycorticosterone; Disease Models, Animal; Disease Susceptibility; Endothelin-1; Hypertension; Kidney Diseases; Male; NF-kappa B; Nitric Oxide; Nitroarginine; Pyrrolidines; Rats; Rats, Sprague-Dawley; Receptor, Endothelin A; Severity of Illness Index; Sodium Chloride, Dietary; Thiocarbamates

The purpose of the study was to investigate renal endothelium-dependent vasodilatation in a model of severe hypertension associated with kidney injury.. Changes in perfusion pressure were measured in isolated, perfused kidneys taken from 18-week-old Wistar-Kyoto rat (WKY), spontaneously hypertensive rats (SHR) and SHR treated for 2 weeks with N(ω) -nitro-L-arginine methyl ester in the drinking water (L-NAME-treated SHR, 6 mg·kg(-1) ·day(-1) ).. Acetylcholine caused similar dose-dependent renal dilatation in the three groups. In vitro administration of indomethacin did not alter the vasodilatation, while the addition of N(w) -nitro-L-arginine (L-NA) produced a differential inhibition of the vasodilatation, (inhibition in WKY > SHR > L-NAME-treated SHR). Further addition of ODQ, an inhibitor of soluble guanylyl cyclase, abolished the responses to sodium nitroprusside but did not affect the vasodilatation to acetylcholine. However, the addition of TRAM-34 (or charybdotoxin) inhibitors of Ca(2+) -activated K(+) channels of intermediate conductance (K(Ca) 3.1), blocked the vasodilatation to acetylcholine, while apamin, an inhibitor of Ca(2+) -activated K(+) channels of small conductance (K(Ca) 2.3), was ineffective. Dilatation induced by an opener of K(Ca) 3.1/K(Ca) 2.3 channels, NS-309, was also blocked by TRAM-34, but not by apamin. The magnitude and duration of NS-309-induced vasodilatation and the renal expression of mRNA for K(Ca) 3.1, but not K(Ca) 2.3, channels followed the same ranking order (WKY < SHR < L-NAME-treated SHR).. In SHR kidneys, an EDHF-mediated response, involving activation of K(Ca) 3.1 channels, contributed to the mechanism of endothelium-dependent vasodilatation. In kidneys from L-NAME-treated SHR, up-regulation of this pathway fully compensated for the decrease in NO availability.

Topics: Acetylcholine; Animals; Apamin; Biological Factors; Endothelium, Vascular; Enzyme Inhibitors; Hypertension; In Vitro Techniques; Indoles; Indomethacin; Intermediate-Conductance Calcium-Activated Potassium Channels; Kidney; Male; NG-Nitroarginine Methyl Ester; Nitric Oxide Synthase; Nitroarginine; Nitroprusside; Oximes; Potassium Channel Blockers; Pyrazoles; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Vasodilation; Vasodilator Agents

Renal prostacycline (PGI(2)) and oxidative stress are known to be important factors that effect the natriurezis and diuresis. 8-iso prostaglandin F(2)α± (8-isoprostane), a member of F(2)-isoprostanes, is formed from the nonenzymatic reaction of arachidonic acid and oxygen radicals in vivo and in vitro, and also it is a marker of oxidative stress in vivo. The aim of this study is to determine the role of renal PGI(2) and 8-isoprostane in a salt and nitric oxide (NO) inhibition-induced hypertension model. Rats were distributed equally among four groups (n = 6 per group). Control rats were given normal salt diet (0.32%); high-salt (HS) rats were given high salt diet (3.2%); NG-nitro-L-arginine (L-NNA) rats were given normal salt diet and 25 mg/kg L-NNA; HS+L-NNA rats were given high salt diet and 25 mg/kg L-NNA. Rats were placed in individual metabolic cages for 17 days. Systolic blood pressure (SBP) was measured at days initial, 7th and 14th .Urinary 8-isoprostane and PGI(2) levels were analyzed. Salt- loading alone did not change SBP values. The average SBP in L-NNA and HS+L-NNA groups were shown to significantly enhance compared to initial and day 7th in the same groups, respectively. The levels of 8-isoprostane in the HS+L-NNA group was significantly enhanced compared to the other groups. L-NNA or HS diet alone did not change the levels of 8-isoprostane compared to the control group. L-NNA alone did not change PGI(2) levels in urine compared to the control. PGI(2) levels in the HS, and the HS+L-NNA group was significantly higher compared to the control group. This study concluded that NOS inhibition plus salt-loading induced oxidative stress and increased renal PGI(2). Also, it is suggested that augmented oxidative stress may aggravate the hypertension. But the renal synthesis of PGI(2) is increased in order to augment the diuresis and natriuresis without the effect of blood pressure (BP).

Topics: Animals; Dinoprost; Disease Models, Animal; Enzyme Inhibitors; Epoprostenol; Hypertension; Male; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Oxidative Stress; Rats; Rats, Sprague-Dawley; Sodium Chloride, Dietary

The aim of this study was to evaluate the role of nitric oxide (NO) in the mechanisms of arterial distensibility and intravascular pressure stability in normotensive and spontaneously hypertensive rats. The experiments were performed on the anesthetized male Wistar, Wistar-Kyoto (WKY), and spontaneously hypertensive rats (SHR). The abdominal aorta was cannulated and perfused with variable blood flow rates with subsequent determination of major characteristics of regional vascular function. The blockade of nitric oxide (NO) synthase resulted in the increase in hydraulic resistance of the hindlimb vascular bed in all series of the experiments. It was associated with the decrease in the intravascular pressure stability. The obtained results provide further evidence for an important role of NO in the formation of conductivity and stability of the arterial pressure both in normo- and hypertensive rats. However, the involvement of NO in the phenomenon of flow-dependent vasodilation in SHR is unlikely. The major difference between SHR and normotensive rats involved the ability of the resistive arteries of SHR to enhance vascular conductivity in response to blood flow enhancement. Presumably, there are some unidentified additional factors that are involved in the flow-dependent vasodilation in SHR.

Topics: Algorithms; Animals; Arteries; Blood Pressure; Catheterization; Enzyme Inhibitors; Hemodynamics; Hyperemia; Hypertension; Male; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Rats, Wistar; Vascular Resistance; Vasodilation

We have previously demonstrated the vasorelaxant activity of 1,3,4-oxadiazole derivative (NOX-1) through L-type Ca2+ channel blockage. In the present study, we investigated whether the correction of endothelial dysfunction is dependent on the normalization of high blood pressure levels by 1,3,4-oxadiazole derivative (NOX-1) in deoxycorticosterone acetate (DOCA-salt) and N(G)-nitro-l-arginine (L-NNA) hypertensive rats. In DOCA-salt and L-NNA hypertensive rats, the mean systolic blood pressure (MSBB) was 185.3+/-4.7 and 170.2+/-4.1 mmHg, whereas after administration of NOX-1 to hypertensive rats, MSBB was 127.8+/-4.5 and 120.2+/-5.1 mmHg, respectively. To study the endothelial dysfunction, concentration-response curves of norepinephrine (NE) and acetylcholine (Ach) were constructed in rat aortic rings isolated from normotensive, hypertensive (DOCA and L-NNA) and NOX-1 treated rats. NE-induced contractions and Ach-induced relaxations were significantly (p<0.05) decreased and increased, respectively in the aorta of NOX-1 treated rats. Vasorelaxant activity of NOX-1 was not abolished by pretreatment of aortic rings with L-NNA, 1H-[1,2,4] oxadiazolo [4,3-A] quinoxalin-1-one (ODQ), indomethacin or glibenclamide. The results suggest that the endothelial dysfunction can be corrected by the L-type Ca2+ channel blocker with endothelium-independent action and that is dependent on the normalization of high blood pressure levels. The antihypertensive and vasorelaxant effects of NOX-1 are mainly endothelial-independent and it can be used to treat hypertension, a state associated with endothelial dysfunction.

Topics: Animals; Antihypertensive Agents; Aorta, Thoracic; Calcium Channel Blockers; Calcium Channels, L-Type; Desoxycorticosterone; Endothelium, Vascular; Enzyme Inhibitors; Glyburide; Hypertension; Indomethacin; Male; Nitroarginine; Norepinephrine; Oxadiazoles; Quinoxalines; Rats; Rats, Wistar; Vasodilation; Vasodilator Agents

Glucocorticoid-induced hypertension is associated with imbalance between nitric oxide (NO) and superoxide. One of the pathways that causes this imbalance is endothelial NO synthase (eNOS) uncoupling. In the present study, adrenocorticotrophic hormone (ACTH)- and dexamethasone-treated rats were further treated with sepiapterin, a precursor of tetrahydrobiopterin, or N-nitro-L-arginine (NOLA), an inhibitor of NOS, to investigate the role of eNOS uncoupling in glucocorticoid-induced hypertension.. Male Sprague-Dawley (SD) rats (n = 7-13/group) were treated with either sepiapterin (5 mg/kg/day, IP) or saline (sham) 4 days before and during ACTH (0.2 mg/kg/day, SC), dexamethasone (0.03 mg/kg/day, SC), or saline treatment. NOLA (0.4 mg/ml in drinking water) was given to rats 4 days before and during dexamethasone treatment. Systolic blood pressure (SBP) was measured by the tail-cuff method.. Both ACTH (116 +/- 2 to 135 +/- 3 mm Hg (mean +/- s.e.m.), P < 0.001) and dexamethasone (114 +/- 4 to 133 +/- 3 mm Hg, P < 0.0005) increased SBP. Sepiapterin alone did not alter SBP. Sepiapterin did not prevent ACTH- (129 +/- 4 mm Hg, NS) or dexamethasone-induced hypertension (135 +/- 3 mm Hg, NS), although plasma total biopterin concentrations were increased. NOLA increased SBP in rats prior to dexamethasone or saline treatment. NOLA further increased SBP in both saline- (133 +/- 4 to 157 +/- 3 mm Hg, P < 0.05) and dexamethasone-treated rats (135 +/- 5 to 170 +/- 6 mm Hg, P < 0.05). ACTH and dexamethasone increased plasma F(2)-isoprostane concentrations. Neither sepiapterin nor NOLA significantly affected this marker of oxidative stress.. Sepiapterin did not prevent ACTH- or dexamethasone-induced hypertension. NOLA exacerbated dexamethasone-induced hypertension. These data suggest that eNOS uncoupling does not play a major role in the genesis of glucocorticoid-induced hypertension in the rat.

Topics: Adrenocorticotropic Hormone; Animals; Biomarkers; Biopterins; Blood Pressure; Dexamethasone; Dietary Supplements; Disease Models, Animal; Enzyme Inhibitors; F2-Isoprostanes; Hypertension; Male; Nitric Oxide Synthase; Nitric Oxide Synthase Type III; Nitroarginine; Oxidative Stress; Pterins; Rats; Rats, Sprague-Dawley

The specific aim of this study was to examine the effects of salt-loading on kidney function and brain antioxidant capacity. Wistar rats were divided into four groups: Control rats were given normal drinking water and no drug treatment for 2 weeks. LNNA group: rats were given normal drinking water and the nitric oxide (NO) inhibitor NG-nitro-L-arginine (L-NNA), 3 mg/kg/day. LNNA + Salt group: rats were given drinking water containing salt 2% and 3 mg/kg L-NNA. Salt group: rats were given drinking water containing salt 2% and no drug treatment. Basal blood pressure and the levels of serum BUN, creatinine, uric acid, cortisol, electrolyte, serum antioxidant capacity, and oxidative stress were measured. NO, superoxide dismutase (SOD), and catalase (CAT) levels were measured in the hypothalamus, brainstem, and cerebellum. Salt overload increased the blood pressure of the LNNA + Salt group. Salt-loading enhanced BUN, creatinine, sodium retention. High salt produced an increase in uric acid levels and a decrease in cortisol levels in serum. Additionally, the oxidative stress index in serum increased in the LNNA + Salt group. Salt-loading enhanced brain NO levels, but not SOD and CAT activity. L-NNA increased brain SOD activity, but not CAT and NO levels. In conclusion, salt-loading causes hypertension, kidney dysfunction, and enhances oxidative stress in salt-sensitive rats.

Topics: Animals; Antioxidants; Brain; Enzyme Inhibitors; Hypertension; Kidney; Nitroarginine; Rats; Rats, Wistar; Salts

Endothelial progenitor cells (EPCs) are both reduced and dysfunctional in hypertension that correlates inversely with its mortality, but the mechanisms are poorly understood. Endothelial nitric oxide synthase (eNOS) critically regulates EPC mobilization and function but is uncoupled in salt-sensitive hypertension because of the reduced cofactor tetrahydrobiopterin (BH4). We tested the hypothesis that GTP cyclohydrolase I (GTPCH I), the rate-limiting enzyme of BH4 de novo synthesis, protects EPCs and its function in deoxycorticosterone acetate (DOCA)-salt mice. EPCs were isolated from peripheral blood and bone marrow of wild-type (WT), WT DOCA-salt, endothelial-specific GTPCH transgenic (Tg-GCH), GTPCH transgenic DOCA-salt, and BH4-deficient hph-1 mice. In WT DOCA-salt and hph-1 mice, EPCs were significantly decreased with impaired angiogenesis and adhesion, which were restored in Tg-GCH DOCA-salt mice. Superoxide (O₂⁻) and nitric oxide (NO) levels in EPCs were elevated and reduced, respectively, in WT DOCA-salt and hph-1 mice; both were rescued in Tg-GCH DOCA-salt mice. eNOS(-/-)/GCH(+/-) hybrid mice demonstrated that GTPCH preserved the circulating EPC number, reduced intracellular O₂⁻ in EPCs, and ameliorated EPC dysfunction independent of eNOS in DOCA-salt hypertension. Secreted thrombospondin-1 (TSP-1; a potent angiogenesis inhibitor) from EPCs was elevated in WT DOCA-salt and hph-1 but not DOCA-salt Tg-GCH mice. In vitro treatment with BH4, polyethylene glycol-superoxide dismutase (PEG-SOD), or Nomega-nitro-L-arginine (L-NNA) significantly augmented NO and reduced TSP-1 and O₂⁻ levels from EPCs of WT DOCA-salt mice. These results demonstrated, for the first time, that the GTPCH/BH4 pathway critically regulates EPC number and function in DOCA-salt hypertensive mice, at least in part, via suppressing TSP-1 expression and oxidative stress.

Topics: Angiogenesis Inhibitors; Animals; Biopterins; Cell Adhesion; Desoxycorticosterone; GTP Cyclohydrolase; Hypertension; Male; Mice; Mice, Inbred C57BL; Mice, Transgenic; Neovascularization, Physiologic; Nitric Oxide; Nitric Oxide Synthase Type III; Nitroarginine; Oxidative Stress; Polyethylene Glycols; Stem Cells; Superoxide Dismutase; Superoxides; Thrombospondin 1

Arterial hyper-responsiveness to 5-hydroxytryptamine (5-HT) is a hallmark of hypertension, and plasma levels of free 5-HT are elevated in hypertension. We hypothesized that chronic administration of 5-HT would cause blood pressure to 1) rise in normotensive rats and 2) rise significantly more in hypertensive rats. The deoxycorticosterone acetate (DOCA)-salt hypertensive and sham normotensive rat were used. Animals were implanted with minipumps that delivered 5-HT (or vehicle) at a rate of 25 microg/kg/min for 7 days. Free plasma 5-HT was elevated significantly by this protocol. Within 48 h, mean arterial blood pressure measured telemetrically decreased in sham (106 +/- 2 to 83 +/- 2 mm Hg) and in DOCA-salt hypertensive (166 +/- 9 to 112 +/- 3 mm Hg) rats; vehicle did not change blood pressure in either group. Ganglionic blockade (hexamethonium) reduced blood pressure to a greater magnitude in DOCA vehicle-administered rats (peak fall arterial pressure, 91 +/- 14 mm Hg) compared with DOCA 5-HT-administered rats (40 +/- 6 mm Hg). Maximal acetylcholine-induced (NO-dependent) relaxation in phenylephrine-contracted aortic strips was greater in 5-HT-administered (69.2 +/- 9.1% relaxation) versus vehicle-administered (39.7 +/- 14.2%) DOCA rats; aortic endothelial cell nitric oxide synthase expression was higher in the 5-HT- versus vehicle-administered DOCA-salt rats. In normotensive and DOCA-salt hypertensive rats, the nitric oxide synthase (NOS) inhibitor N(omega)-nitro-l-arginine (0.5 g/l in water) prevented the fall in blood pressure to 5-HT. We conclude that chronic exogenous 5-HT reduces blood pressure in normotensive and hypertensive rats through mechanisms critically dependent on NOS.

Topics: Animals; Antihypertensive Agents; Aorta, Thoracic; Blood Pressure; Desoxycorticosterone; Hypertension; Isometric Contraction; Male; Nitric Oxide Synthase; Nitroarginine; Rats; Rats, Sprague-Dawley; Serotonin

Previous investigations have indicated that angiotensin II (Ang II)-induced hypertension and endothelial dysfunction are prevented by intake of red wine polyphenols (RWPs). Ang II has also been shown to increase the expression of VEGF and MMP-2, two major pro-inflammatory factors, in vascular diseases. Therefore, the aim of the present study was to determine whether intake of RWPs is able to prevent these effects in rats and, if so, to characterize the underlying mechanism.. VEGF and endothelial NO synthase (eNOS) expression was assessed by immunofluorescence and Western blotting, MMP-2 activity by zymography, and reactive oxygen species (ROS) formation by dihydroethidine.. Ang II increased VEGF expression and MMP-2 activity in the aortic wall. Ang II-induced MMP-2 activation is inhibited by N(G)-nitro-L-arginine and MnTMPyP. Ang II increased the expression of eNOS, the formation of ROS and the nitration of proteins. The stimulatory effects of Ang II on these factors are prevented by RWPs intake.. Infusion of Ang II induced vascular expression of VEGF and peroxynitrite-dependent activation of MMP-2, with both effects being prevented by RWPs intake. Thus, prevention of VEGF and MMP-2 expression might be involved in the protective effect of red wine on coronary heart diseases.

Topics: Angiotensin II; Animals; Antihypertensive Agents; Aorta; Blood Pressure; Blotting, Western; Disease Models, Animal; Enzyme Inhibitors; Flavonoids; Fluorescent Antibody Technique; Hypertension; Male; Matrix Metalloproteinase 2; Metalloporphyrins; Nitric Oxide; Nitric Oxide Synthase Type II; Nitric Oxide Synthase Type III; Nitroarginine; Peroxynitrous Acid; Phenols; Polyphenols; Rats; Rats, Sprague-Dawley; Reactive Oxygen Species; Time Factors; Up-Regulation; Vascular Endothelial Growth Factor A; Wine

Although, there are some evidences on the contribution of increased sympathoadrenergic activity on long-term nitric oxide synthase (NOS) inhibition induced hypertension, the contribution of sympathetic activity to the development of this model of hypertension are not sufficiently studied. The aim of the present study is to investigate the effects of clonidine on blood pressure and vascular alpha-adrenergic receptors in the long-term N (omega)-nitro-L-arginine (L-NNA) treated rats.. Sixty two Wistar rats were randomly divided into 8 groups. All groups were administrated L-NNA and/or clonidine in two different concentrations for ten days. L-NNA was administrated in concentrations of 15 and 45 mg/100ml to L-NNA15 and L-NNA45 groups, respectively. Clonidine was also administrated in concentrations of 150 and 225 microg/100ml to KLO150 and KLO225 groups, respectively. Blood pressure and heart rates were measured with tail-cuff method and plasma NOx levels with spectrophotometer. The a-adrenoreceptors responses were evaluated in thoracic aorta rings in "in vitro" conditions.. Clonidine prevented the L-NNA induced hypertension dose-dependently, but did not effect the heart rates decreased by L-NNA. The heart rates and blood pressure of normotensive rats were not changed by clonidine alone. Plasma NOx levels increased in L-NNA15 group (0.62+/-0.11 micromol/L, p=0.003) but did not change in other groups. The sensitivity of aorta to phenylephrine (-7.33+/-0.11 micromol/L, p=0.001) and clonidine (-7.60+/-0.27 micromol/L, p=0.003) in L-NNA45 group and phenylephrine (-6.94+/-0.13 micromol/L, p=0.002) in L-NNA15 group increased. The sensitivity of aorta to phenylephrine (7.93+/-0.16 micromol/L, p=0.001) in KLO225 group and to clonidine (-7.20+/-0.10 micromol/L, p=0.009) in KLO150 group increased.. This study supports the idea suggesting that symphathetic nervous system activation is partly responsible for the development of the long-term NOS inhibition induced hypertension. In conclusion, it was shown for the first time that clonidine prevents the development of long-term NOS inhibition induced hypertension dose-dependently.

Topics: Animals; Antihypertensive Agents; Aorta, Thoracic; Blood Pressure; Clonidine; Disease Models, Animal; Dose-Response Relationship, Drug; Endothelium, Vascular; Enzyme Inhibitors; Heart Rate; Hypertension; Male; Nitroarginine; Random Allocation; Rats; Rats, Wistar

In human essential hypertension (EH), endothelium-dependent relaxation can occur independent of nitric oxide (NO) and prostacyclin (PGI(2)). Recent in vivo data suggest that rapid compensatory upregulation of endothelial cytochrome P450 epoxygenase 2C9 occurs to preserve vasorelaxation under conditions of decreased NO bioavailability. As one of the vascular actions of CYP2C9 is to modulate small and intermediate conductance endothelial calcium-activated potassium channels (SK(Ca) and IK(Ca)), we examined whether endothelium-dependent relaxation is sensitive to inhibitors of these channels (apamin and charybdotoxin) in resistance-sized vessels from human with EH. Subcutaneous gluteal biopsies were performed on 12 humans with EH and 12 matched control subjects. Resistance arteries were dissected and relaxation responses to carbachol were assessed ex vivo using wire myography in the presence of: (i) N(G)-nitro-L-arginine (L-NOARG)/indomethacin; and (ii) apamin/charybdotoxin. Maximal carbachol relaxation was impaired in EH vs control subjects. No differences in responses were observed with the endothelium-independent agonist, S-nitroso-N-acetyl-penicillamine. Relaxation to carbachol was attenuated following incubation with L-NOARG/indomethacin in vessels from control subjects (P<0.01 analysis of variance (ANOVA)), but not in vessels from patients with EH. The reverse pattern was seen following apamin/charybdotoxin with carbachol relaxation attenuated only in EH vessels (P<0.001 ANOVA). Endothelium-dependent relaxation is resistant to endothelial nitric oxide synthase inhibition but sensitive to blockade of calcium-activated potassium channels in human EH. Studies with more specific inhibitors are required to determine whether this response is mediated by endothelial potassium channel subtypes (SK(Ca) and IK(Ca)).

Topics: Adult; Aged; Analysis of Variance; Apamin; Biopsy; Buttocks; Calcium Channel Blockers; Carbachol; Case-Control Studies; Charybdotoxin; Endothelium, Vascular; Humans; Hypertension; Indomethacin; Male; Middle Aged; Nitric Oxide; Nitroarginine; Norepinephrine; Potassium Channels, Calcium-Activated

Nitric oxide (NO) is important for the homeostasis of organ functions. We studied the structural and functional changes in the cardiovascular (CV) and renal systems following early NO deprivation by various nonspecific and specific NO synthase (NOS) inhibitors: N-nitro-L-arginine methyl ester (L-NAME), N-nitro-L-arginine (L-NA), S-methyl-isothiourea (SMT), and L-N6-(1-iminoethyl)-lysine (L-Nil). The aim is to elucidate the involvement of NO through endothelial or inducible NOS (eNOS and iNOS). Drugs were given to spontaneously hypertensive rats (SHR) and age-matched normotensive Wistar Kyoto rats (WKY) from a young age (5-wk-old). Physiological, biochemical, and pathological examinations were performed. L-NAME and L-NA treatment caused a rapid increase in tail cuff pressure (TCP). The TCP of SHR reached a malignant level within 30 days with signs of stroke, proteinuria [corrected] severe glomerular sclerosis, and moderate ventricular hypertrophy (VH). The plasma nitrite/nitrate was reduced, while creatinine, urea nitrogen and uric acid were elevated. The renal tissue cyclic guanosine monophosphate (cGMP) was decreased with an elevated collagen content. The numbers of sclerotic glomeruli, arteriolar and glomerular injury scores were markedly increased, accompanied by reduction in renal blood flow, filtration rate, and fraction. Plasma endothelin-1 was increased following L,-NAME or L-NA treatment for 10 days. The expression of eNOS and iNOS mRNA was depressed by L-NAME and L-NA. The relevant iNOS inhibitors, SMT and L-Nil depressed the iNOS expression, but did not produce significant changes in CV and renal systems. The continuous release of NO via the eNOS system provides a compensatory mechanism to prevent the genetically hypertensive rats from rapid progression to malignant phase. Removal of this compensation results in VH, stroke, glomerular damage, renal function impairment, and sudden death.

Topics: Animals; Blood Pressure; Blood Urea Nitrogen; Body Weight; Endothelin-1; Enzyme Inhibitors; Glomerular Filtration Rate; Hypertension; Isothiuronium; Kidney; Kidney Function Tests; Lysine; Muscle Weakness; NG-Nitroarginine Methyl Ester; Nitrates; Nitric Oxide Synthase; Nitric Oxide Synthase Type II; Nitric Oxide Synthase Type III; Nitrites; Nitroarginine; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Renal Circulation; Ventricular Function, Left

Cysteinyl leukotrienes (cysLT) are pro-inflammatory and vasoactive products suspected to be involved in the regulation of vascular tone and blood pressure in hypertension.. We investigated, in spontaneously hypertensive rats (SHR), the involvement of cysLT in the in-vivo regulation of blood pressure and the in-vitro endothelium-dependent contraction to acetylcholine in isolated aorta.. SHR and Wistar-Kyoto rats (WKY) were orally treated for 3 weeks with either the cysLT biosynthesis inhibitor MK-886 (0.1 mg/ml) or vehicle. After mean arterial blood pressure (MABP) measurement, aortic ring preparations were removed from all groups of animals, and contractions and relaxations were monitored subsequent to stimulation with acetylcholine.. MABP was higher in SHR. Chronic treatment with MK-886 did not alter MABP in either SHR or WKY. In the presence of the N-nitro-L-arginine (L-NA, 100 micromol/l), and on prostaglandin F2alpha (PGF2alpha)-induced tone, acetylcholine evoked concentration-dependent contractions in intact aortic rings from SHR only. Pretreatment with either MK-886 (10 micromol/l), the 5-lipoxygenase (5-LO) inhibitor AA861 (10 micromol/l), or the cysLT1 receptor antagonist MK571 (1 micromol/l) reduced (P < 0.05) acetylcholine-induced contractions in intact aortic rings from SHR only. Acetylcholine-induced contractions were weaker (P < 0.01) in SHR chronically treated with MK-886 than in SHR. In the presence of L-NA, leukotriene (LT) D4 induced greater (P < 0.05) concentration-dependent contractions in aortic rings from SHR than from WKY. MK571 abolished LTD4-evoked contractions.. These data suggested that 5-LO-derived products, through the activation of cysLT1 receptors, could be involved in the endothelium-dependent contraction to acetylcholine in aorta from SHR but not in the regulation of MABP in SHR.

Topics: Acetylcholine; Animals; Aorta, Thoracic; Arachidonate 5-Lipoxygenase; Benzoquinones; Biopterins; Blood Pressure; Body Weight; Dinoprost; Endothelium, Vascular; Hypertension; Indoles; Leukotriene D4; Lipoxygenase Inhibitors; Male; Membrane Proteins; Nitroarginine; Propionates; Quinolines; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Receptors, Leukotriene; Vasoconstriction

We investigated how hypertension during pregnancy affected passive structural (wall:lumen, wall stress) and active (myogenic activity) responses of the cerebral circulation. Female nonpregnant (NP; n=8) Sprague Dawley rats were compared with late-pregnant (LP; day 19 to 20, n=6) rats. Some animals were treated with the NO synthase inhibitor nitro-L-arginine in their drinking water to raise blood pressure. LP rats (n=6) were treated for the last 7 days of pregnancy (last trimester) to mimic preeclampsia and compared with NP rats treated for the same duration (n=8). Active and passive responses were determined on isolated and pressurized third-order posterior cerebral arteries. Nitro-L-arginine treatment significantly raised blood pressure in both groups of animals that was associated with increased wall thickness and wall:lumen ratio in the NP hypertensive animals versus controls (P<0.05). In contrast, this response to pressure was absent in LP animals, which had similar wall measurements. In addition, arteries from NP hypertensive animals had increased myogenic tone and pressure of forced dilatation compared with NP control animals (P<0.01). Again, this response was lacking in the LP hypertensive animals that had similar tone and pressure of forced dilatation as normotensive controls. The increased tone and wall thickness decreased wall stress in the NP hypertensive animals, a response that did not occur in LP hypertensive animals. Because medial hypertrophy is considered a protective response to elevated blood pressure, these results suggest that hypertension in pregnancy may predispose the cerebral circulation to autoregulatory breakthrough and blood-brain-barrier disruption when blood pressure is elevated, as during eclampsia.

Topics: Animals; Blood Pressure; Blood-Brain Barrier; Cerebral Arteries; Eclampsia; Enzyme Inhibitors; Female; Gestational Age; Homeostasis; Hypertension; Microscopy, Video; Nitric Oxide Synthase; Nitroarginine; Pre-Eclampsia; Pregnancy; Pregnancy Complications, Cardiovascular; Rats; Rats, Sprague-Dawley

We reported upregulation of the 5-hydroxytryptamine (HT) transporter (5-HTT) protein in peripheral arteries from deoxycorticosterone acetate (DOCA)-salt hypertensive rats. We hypothesized that upregulated 5-HTT may be generally elevated in hypertensive models and, as a consequence, a higher basal concentration of 5-HT, the 5-HT metabolite 5-hydroxyindoleacetic acid, and an increased 5-HT uptake would occur in peripheral arteries of hypertensive rats compared with normotensive rats. We examined 3 hypertension models: DOCA-salt rats, Nomega-nitro-L-arginine (LNNA) rats, and spontaneously hypertensive rats (SHRs) in our study (systolic blood pressure [mm Hg]: DOCA (D)=197+/-6, SHAM(D)=112+/-4, LNNA (L)=228+/-9, SHAM(L)=128+/-2, SHR=172+/-7, and Wistar-Kyoto [WKY]= 121+/-3). High-pressure liquid chromatography measurements showed lower basal 5-HT concentrations in aorta from DOCA-salt and LNNA rats compared with their SHAM rats but not in SHR compared with WKY. In all of the 5-HT-uptake studies, we used arteries isolated from rats treated with the monoamine oxidase-A inhibitor pargyline to minimize 5-HT metabolism. Exogenous 5-HT was taken up by aorta, and this was inhibited by the 5-HTT inhibitor fluoxetine (1 micromol/L) or fluvoxamine (1 micromol/L). Total 5-HT uptake and 5-HTT-dependent active 5-HT uptake were decreased in aorta from DOCA-salt and LNNA rats compared with SHAM rats, but this was not observed in SHRs compared with WKYs. Western analysis revealed similar expression of 5-HTT in aorta from WKYs and SHRs as opposed to an upregulated 5-HTT in aorta from DOCA-salt and LNNA-hypertensive rats. Our study suggested that an altered serotonergic system by impaired 5-HTT function might play a role in blood pressure regulation in DOCA-salt and LNNA-hypertensive rats.

Topics: Animals; Aorta; Desoxycorticosterone; Hypertension; Male; Nitroarginine; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Rats, Sprague-Dawley; Serotonin; Serotonin Plasma Membrane Transport Proteins; Up-Regulation

Loss of endothelial cell-derived nitric oxide (NO) in hypertension is a hallmark of arterial dysfunction. Experimental hypertension created by the removal of NO, however, involves mechanisms in addition to decreased arterial vasodilator activity. These include augmented endothelin-1 (ET-1) release, increased sympathetic nervous system activity, and elevated tissue oxidative stress. We hypothesized that increased venous smooth muscle (venomotor) tone plays a role in Nomega-nitro-L-arginine (LNNA) hypertension through these mechanisms. Rats were treated with the NO synthase inhibitor LNNA (0.5 g/L in drinking water) for 2 weeks. Mean arterial pressure of conscious rats was 119 +/- 2 mm Hg in control and 194 +/- 5 mm Hg in LNNA rats (P<0.05). Carotid arteries and vena cava were removed for measurement of isometric contraction. Maximal contraction to norepinephrine was modestly reduced in arteries from LNNA compared with control rats whereas the maximum contraction to ET-1 was significantly reduced (54% control). Maximum contraction of vena cava to norepinephrine (37% control) also was reduced but no change in response to ET-1 was observed. Mean circulatory filling pressure, an in vivo measure of venomotor tone, was not elevated in LNNA hypertension at 1 or 2 weeks after LNNA. The superoxide scavenger tempol (30, 100, and 300 micromol kg(-1), IV) did not change arterial pressure in control rats but caused a dose-dependent decrease in LNNA rats (-18 +/- 8, -26 +/- 15, and -54 +/- 11 mm Hg). Similarly, ganglionic blockade with hexamethonium caused a significantly greater fall in LNNA hypertensive rats (76 +/- 9 mm Hg) compared with control rats (35 +/- 10 mm Hg). Carotid arteries, vena cava, and sympathetic ganglia from LNNA rats had higher basal levels of superoxide compared with those from control rats. These data suggest that while NO deficiency increases oxidative stress and sympathetic activity in both arterial and venous vessels, the impact on veins does not make a major contribution to this form of hypertension.

Topics: Animals; Antioxidants; Arteries; Blood Pressure; Cyclic N-Oxides; Endothelin-1; Enzyme Inhibitors; Ganglia, Sympathetic; Hypertension; In Vitro Techniques; Male; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Oxidative Stress; Rats; Rats, Sprague-Dawley; Spin Labels; Superoxides; Vasoconstriction; Veins

Smooth muscle membrane potential (E(m)) depends on K(+) channels, and arteries from rats made hypertensive with N(omega)-nitro-l-arginine (LHR) are depolarized compared with control. We hypothesized that decreased K(+) channel function, due to decreased K(+) channel protein expression, underlies E(m) depolarization. Furthermore, K(+) channel blockers should move control E(m) (-46 +/- 1 mV) toward that in LHR (-37 +/- 2 mV) and normalize contraction. The E(m) vs. K(+) relationship was less steep in LHR (23 +/- 2 vs. 28 +/- 1 mV/log K(+) concentration), and contractile sensitivity to K(+) was increased (EC(50) = 37 +/- 1 vs. 23 +/- 1 mM). Iberiotoxin (10 nM), an inhibitor of large-conductance Ca(2+)-activated K(+) (BK(Ca)) channels, depolarized control and LHR E(m) to -35 +/- 1 and -30 +/- 2 mV, respectively; however, effects on K(+) sensitivity were more profound in LHR (EC(50) = 25 +/- 2 vs. 15 +/- 3 mM). The voltage-dependent K(+) (K(V)) channel blocker 4-aminopyridine (3 mM) depolarized control E(m) to the level of LHR (-28 +/- 1 vs. -28 +/- 1 mV); however, effects on K(+) sensitivity were greater in LHR (EC(50) = 17 +/- 4 vs. 4 +/- 4 mM). Western blots revealed reduced BK(Ca) and K(V)1.5 channel expression in LHR arteries. The findings suggest that diminished expression of K(+) channels contributes to depolarization and enhanced contractile sensitivity. These conclusions are supported by direct electrophysiological assessment of BK(Ca) and K(V) channel function in control and LHR smooth muscle cells.

Topics: Animals; Blotting, Western; Enzyme Inhibitors; Hypertension; Male; Membrane Potentials; Mesenteric Arteries; Muscle, Smooth, Vascular; Nitroarginine; Patch-Clamp Techniques; Potassium; Potassium Channel Blockers; Potassium Channels; Rats; Rats, Sprague-Dawley; Vasoconstriction

Hypertension demands cardiac synthetic and metabolic adaptations to increased afterload. We studied gene expression in two models of mild hypertension without overt left ventricular hypertrophy using the NO synthase inhibitor nitro-L-arginine (L-NNA) and the glutathione depletor buthionine-S,R-sulfoximine (BSO). Mice were administered L-NNA, BSO, or water for 8 weeks. RNA of left ventricles was pooled per group, reverse transcribed, Cy3 and Cy5 labeled, and hybridized to cDNA microarrays. Normalized log(2) Cy3/Cy5 ratios of > or =0.7 or < or =-0.7 were considered significant. L-NNA and BSO both caused hypertension. Gene expression was regulated in cytoskeletal components in both models, protein synthesis in L-NNA-treated mice, and energy metabolism in BSO-treated mice. Energy metabolism genes shared several common transcription factor-binding sites such as Coup-Tf2, of which gene expression was increased in BSO-treated mice, and COMP-1. Characterization of the left ventricular adaptations as assessed with gene expression profiles reveals differential expression in energy and protein metabolism related to the pathogenetic background of the hypertension.

Topics: Animals; Binding Sites; Blood Pressure; Body Weight; Buthionine Sulfoximine; Cluster Analysis; Energy Metabolism; Enzyme Inhibitors; Female; Gene Expression; Gene Expression Profiling; Glutamate-Cysteine Ligase; Glutathione; Glycolysis; Heart; Heart Ventricles; Hypertension; Hypertrophy, Left Ventricular; Mice; Mice, Inbred C57BL; Myocardium; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Oligonucleotide Array Sequence Analysis; Organ Size; Protein Biosynthesis; Proteinuria; Reverse Transcriptase Polymerase Chain Reaction; Transcription Factors

Smooth muscle membrane potential is determined, in part, by K(+) channels. In the companion paper to this article, we demonstrated that superior mesenteric arteries from rats made hypertensive with N(omega)-nitro-l-arginine (l-NNA) are depolarized and express less K(+) channel protein compared with those from normotensive rats. In the present study, we used patch-clamp techniques to test the hypothesis that l-NNA-induced hypertension reduces the functional expression of K(+) channels in smooth muscle. In whole cell experiments using a Ca(2+)-free pipette solution, current at 0 mV, largely due to voltage-dependent K(+) (K(V)) channels, was reduced approximately 60% by hypertension (2.7 +/- 0.4 vs. 1.1 +/- 0.2 pA/pF). Current at +100 mV with 300 nM free Ca(2+), largely due to large-conductance Ca(2+)-activated K(+) (BK(Ca)) channels, was reduced approximately 40% by hypertension (181 +/- 24 vs. 101 +/- 28 pA/pF). Current blocked by 3 mM 4-aminopyridine, an inhibitor of many K(V) channel types, was reduced approximately 50% by hypertension (1.0 +/- 0.4 vs. 0.5 +/- 0.2 pA/pF). Current blocked by 1 mM tetraethylammonium, an inhibitor of BK(Ca) channels, was reduced approximately 40% by hypertension (86 +/- 14 vs. 53 +/- 19 pA/pF). Differences in BK(Ca) current magnitude are not attributable to changes in single-channel conductance or Ca(2+)/voltage sensitivity. The data support the hypothesis that l-NNA-induced hypertension reduces K(+) current in vascular smooth muscle. Reduced molecular and functional expression of K(+) channels may partly explain the depolarization and augmented contractile sensitivity of smooth muscle from l-NNA-treated rats.

Topics: Animals; Delayed Rectifier Potassium Channels; Enzyme Inhibitors; Hypertension; Male; Membrane Potentials; Muscle, Smooth, Vascular; Nitric Oxide; Nitroarginine; Patch-Clamp Techniques; Potassium Channels, Calcium-Activated; Potassium Channels, Voltage-Gated; Rats; Rats, Sprague-Dawley

The aim of this study was to evaluate the impact of poisoning with cadmium in hypertensive doses (50 or 200 ppm in drinking water for three months) on the basal and stimulated release NO effect in the isolated and perfused rat mesenteric bed. Mesenteric artery preparation preconstricted by norepinephrine (0.5 microg/mL) was used to determine changes in its vascular resistance induced by e-NOS synthase blocker, N-omega-nitro-L-arginine (L-NOARG) injected in increasing doses from 1.0 to 200.0 microg or acetylcholine (ACh) administered in doses from 0.05 x 10(-10) to 5.0 x 10(-10) mol before and during L-NOARG infusion (1.0 microg/mL). Vascular reactivity was measured as an increase or decrease in perfusion pressure in the constant flow system. Rats poisoned with 50 or 200 ppm of cadmium demonstrated a significant decrease (P <0.05) in vascular response to L-NOARG used in doses of 50 or 100 microg. The dose-response curve obtained for L-NOARG was shifted to the right and ED50 value was greater in the group of rats given cadmium in a dose of 200 ppm than in the controls (70.3 +/- 10.7 versus 25.7 +/- 4.8 microg, P <0.01). These rats reacted with lower expressed vasodilatation to ACh in doses to 0.2 x 10(-10) mol. In all poisoned rats, L-NOARG enhanced the effect of ACh used in doses from 0.05 to 0.5 x 10(-10) mol, whereas in the control group this effect was only achieved at 0.1 x 10(-10) mol. The serum nitric oxide concentration was decreased (P <0.05) in both groups of cadmium-treated rats. These results suggest that cadmium in hypertensive doses modifies the vascular effect of NO in basal conditions and after stimulation by ACh.

Topics: Acetylcholine; Animals; Cadmium Chloride; Cadmium Poisoning; Dose-Response Relationship, Drug; Hypertension; Male; Mesenteric Arteries; Muscle, Smooth, Vascular; Nitric Oxide; Nitric Oxide Synthase; Nitric Oxide Synthase Type III; Nitroarginine; Norepinephrine; Rats; Rats, Inbred BUF; Vasoconstriction; Vasoconstrictor Agents; Vasodilator Agents

This study tested the hypothesis that nitric oxide (NO) synthase inhibition in mice would result in hypertension characterized by increased agonist-induced vasoconstrictor responsiveness and attenuated endothelium-dependent vasodilation. Administration of N-nitro-L-arginine (L-NNA), an NO synthase inhibitor (1 g/L, 4 weeks), via drinking water to mice resulted in significant elevations in blood pressure. Phenylephrine-induced contraction was significantly increased in aortic rings from L-NNA-treated mice compared with rings from control mice. Aortic rings from control mice showed a concentration-dependent relaxation to acetylcholine whereas those obtained from L-NNA-treated mice showed a biphasic response, contracting at lower concentrations while relaxing at higher concentrations. Aortic rings from L-NNA-treated mice had decreased relaxation to acetylcholine and increased sensitivity to sodium nitroprusside compared with control rings. The relaxation induced by an NO-independent soluble guanylyl cyclase activator was not different between groups. In aortic rings from control and L-NNA-treated mice pre-contracted with phenylephrine, the administration of L-NNA to the organ bath caused additional and sustained contraction. When compared with the contraction induced by phenylephrine, L-NNA-induced contraction in aorta from control mice was significantly higher than that in aorta from L-NNA-treated mice. We conclude that mice treated with L-NNA develop hypertension and that a reduction in NO availability is responsible for the changes observed in vascular reactivity.

Topics: Acetylcholine; Animals; Aorta; Blood Pressure; Dose-Response Relationship, Drug; Endothelium, Vascular; Enzyme Activators; Enzyme Inhibitors; Heart Rate; Hypertension; In Vitro Techniques; Indazoles; Male; Mice; Muscle Relaxation; Muscle, Smooth, Vascular; Nitric Oxide Synthase; Nitroarginine; Nitroprusside; Phenylephrine; Vasoconstriction; Vasoconstrictor Agents; Vasodilation; Vasodilator Agents

In this work, we aimed to observe the changes in adrenomedullin (ADM) and its receptor-calcitonin receptor-like receptor (CL), receptor activity-modifying protein (RAMP) 1, RAMP2 and RAMP3-in cardiac ventricles and aortas of hypertensive rats, and the responsiveness of injured cardiovascular tissue to ADM, then to illustrate the protective mechanism of ADM on the cardiovascular system. Male SD rats were subjected to treatment with chronic N(G)-nitro-L-arginine (L-NNA), an inhibitor of nitric oxide synthase. The ADM contents and cAMP production in myocardia and aortas were measured by RIA. The mRNA levels of ADM, CL, and RAMP1-3 were determined by RT-PCR. L-NNA induced severe hypertension and cardiomegaly. The ir-ADM content in plasma, ventricles and aortas in L-NNA-treated animals increased by 80%, 72% and 57% (all p<0.01), respectively. Furthermore, mRNA levels of ADM, CL, RAMP2 and RAMP3 were elevated by 91%, 33%, 50% and 72.5% (all p<0.01), respectively, in ventricles and by 95%, 177%, 74.7% and 85% (all p<0.01), respectively, in aortas. mRNA level of RAMP1 was elevated by 129% (p<0.01) in aortas but no significant difference in ventricles. The elevated mRNA levels of RAMP2 and RAMP3 were positively correlated with that of ADM in hypertrophic ventricles (r=0.633 and 0.828, p<0.01, respectively) and the elevated mRNA levels of CL, RAMP2 and RAMP3 were positively correlated with that of ADM in aortas (r=0.941, 0.943 and 0.736, all p<0.01, respectively). The response of ventricular myocardia and aortas to ADM administration potentiated, and the production of cAMP was increased by 41% and 68% (both p<0.01), respectively. ADM-stimulated cAMP generation in ventricular myocardia and aortas was blocked by administration of both ADM22-52, the specific antagonist of ADM receptor, and CGRP8-37, the antagonist of the CGRP1 receptor. The results showed an increased in cardiovascular ADM generation and an up-regulation of the gene expression of ADM and its receptor-CL, RAMP1-3 during hypertension, augmented responsiveness of ventricular myocardia and aortas of hypertensive rats to ADM, suggesting that these receptors may play a role in the cardiovascular adaptation in response to sub-chronic NO-inhibition.

Topics: Adrenomedullin; Animals; Antihypertensive Agents; Aorta; Cyclic AMP; Disease Models, Animal; Enzyme Inhibitors; Heart; Heart Ventricles; Hypertension; Intracellular Signaling Peptides and Proteins; Male; Myocardium; Nitroarginine; Peptides; Rats; Rats, Sprague-Dawley; Receptors, Calcitonin; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger

We assessed the effect of nitric oxide (NO) synthase inhibition on plasma atrial natriuretic peptide (ANP) concentration and content in some brain structures [neurohypophysis (NH), adenohypophysis (AH), medial basal hypothalamus (MHB) and olfactory bulb (OB)] in rats before and after blood volume expansion (BVE). Male Wistar rats were injected i.p. with N(pi)-nitro-L-arginine (L-NNA), 25 mg/kg of body weight, 40 min before the experiment (acute treatment) or L-NNA at a dose of 25 mg/kg body weight, twice a day, for 4 days (chronic treatment). The acute treatment caused an increase in the blood pressure and plasma ANP concentration in rats under basal conditions and after BVE. A decrease in ANP content was observed in the OB and NH, whereas no significant changes were found in the AH or MBH. In chronically treated rats, we also found an increase in blood pressure and in plasma ANP concentration under basal conditions and after BVE. The ANP content increased in the OB, NH and AH. These results indicate that systemic NO synthase inhibition increases ANP concentration in plasma and in areas of the central nervous system. We hypothesize that ANP participates in the hypertension-induced by NO synthesis blockade acting by baroreceptors input to the brain to stimulate ANP release and synthesis that reduces NO prival hypertension.

Topics: Animals; Atrial Natriuretic Factor; Blood Pressure; Brain; Hypertension; Male; Nitric Oxide Synthase; Nitroarginine; Rats; Rats, Wistar

Eclampsia is thought to be similar to hypertensive encephalopathy, whereby acute elevations in intravascular pressure cause forced dilatation (FD) of intrinsic myogenic tone of cerebral arteries and arterioles, decreased cerebrovascular resistance, and hyperperfusion. In the present study, we tested the hypothesis that pregnancy and/or the postpartum period predispose cerebral arteries to FD by diminishing pressure-induced myogenic activity. We compared the reactivity to pressure (myogenic activity) as well as factors that modulate the level of tone of third-order branches (<200 microm) of the posterior cerebral artery (PCA) that were isolated from nonpregnant (NP, n = 7), late-pregnant (LP, 19 days, n = 10), and postpartum (PP, 3 days, n = 8) Sprague-Dawley rats under pressurized conditions. PCAs from all groups of animals developed spontaneous tone within the myogenic pressure range (50-150 mmHg) and constricted arteries at 100 mmHg (NP, 30 +/- 3; LP, 39 +/- 4; and PP, 42 +/- 7%; P > 0.05). This level of myogenic activity was maintained in the NP arteries at all pressures; however, both LP and PP arteries dilated at considerably lower pressures compared with NP, which lowered the pressure at which FD occurred from >175 for NP to 146 +/- 6.5 mmHg for LP (P < 0.01 vs. NP) and 162 +/- 7.7 mmHg for PP (P < 0.01 vs. NP). The amount of myogenic tone was also significantly diminished at 175 mmHg compared with NP: percent tone for NP, LP, and PP animals were 35 +/- 2, 11 +/- 3 (P < 0.01 vs. NP), and 20 +/- 7% (P < 0.01 vs. NP), respectively. Inhibition of nitric oxide (NO) with 0.1 mM N(omega)-nitro-l-arginine (l-NNA) caused constriction of all vessel types that was significantly increased in the PP arteries, which demonstrates significant basal NO production. Reactivity to 5-hydroxytryptamine (serotonin) was assessed in the presence of l-NNA and indomethacin. There was a differential response to serotonin: PCAs from NP animals dilated, whereas LP and PP arteries constricted. These results suggest that both pregnancy and the postpartum period predispose the cerebral circulation to FD at lower pressures, a response that may lower cerebrovascular resistance and promote hyperperfusion when blood pressure is elevated, as occurs during eclampsia.

Topics: Animals; Blood Pressure; Cerebral Arteries; Cerebrovascular Circulation; Cyclooxygenase Inhibitors; Eclampsia; Enzyme Inhibitors; Female; Hypertension; Nitric Oxide; Nitroarginine; Postpartum Period; Pregnancy; Pregnancy Complications, Cardiovascular; Rats; Rats, Sprague-Dawley; Serotonin; Vascular Resistance; Vasoconstriction

Salt-sensitive hypertension is associated with impaired NO/cGMP signaling. We hypothesized that increased superoxide production by NADPH oxidase and altered endothelial NO synthase (NOS3) phosphorylation determine endothelial dysfunction in hypertension. Experiments tested if NO/cGMP signaling and NOS3 serine phosphorylation are decreased and NADPH oxidase activity is increased in mesenteric arteries from deoxycorticosterone acetate (DOCA)-salt rats compared with arteries from placebo rats. Concentration response curves to phenylephrine were performed in mesenteric arteries in the presence and absence of Nomega-nitro-L-arginine (LNA) and antioxidants to determine the influence of basal NO and superoxide production on vascular tone. LNA increased phenylephrine sensitivity in arteries from placebo, but not DOCA-salt rats, regardless of antioxidant treatment. To determine basal cGMP production, mesenteric arteries were incubated with 3-isobutyl-1-methylxanthine in the presence or absence of LNA, sodium nitroprusside (SNP), antioxidants, or tetrahydrobiopterin. NOS-dependent cGMP production was reduced in arteries from DOCA-salt rats compared with arteries from placebo rats and was not restored by acute treatment with antioxidants or tetrahydrobiopterin. SNP-induced cGMP production was similar between groups as was NADPH oxidase activity, measured by lucigenin chemiluminescence, in mesenteric arteries. Expression and phosphorylation of NOS3 were examined by Western blotting. Phosphorylation of NOS3 was decreased in arteries from DOCA-salt rats compared with placebo at serine residues 1179 and 635. These findings indicate that diminished NO/cGMP signaling in mesenteric arteries from DOCA-salt rats is caused by reduced phosphorylation of NOS3 at serine 1179 and serine 635, rather than NO scavenging by superoxide.

Topics: Adrenergic alpha-Agonists; Animals; Antioxidants; Biopterins; Codon; Cyclic GMP; Desoxycorticosterone; Hypertension; Male; Mesenteric Arteries; NADPH Oxidases; Nitric Oxide; Nitric Oxide Synthase; Nitric Oxide Synthase Type III; Nitroarginine; Nitroprusside; Phenylephrine; Phosphorylation; Phosphoserine; Polyethylene Glycols; Protein Processing, Post-Translational; Rats; Rats, Sprague-Dawley; Signal Transduction; Sodium Chloride, Dietary; Superoxide Dismutase

We investigated whether chronic ouabain treatment changes the vasoconstrictor responses induced by electrical field stimulation (EFS) in endothelium-denuded rat superior mesenteric arteries and a possible role of neuronal nitric oxide (NO).. Mesenteric arteries from untreated and ouabain-treated rats (approximately equal to 8.0 microg/kg per day, for 5 weeks) were used in this study. Vascular reactivity was analyzed by isometric tension recording. Expression of the neuronal NO synthase isoform was analyzed by Western blot. Noradrenaline release was evaluated in segments incubated with [H]noradrenaline.. Systolic (SBP) and diastolic (DBP) blood pressure were higher in ouabain-treated rats than in untreated rats (SBP, untreated: 120 +/- 3.5 mmHg versus ouabain-treated: 150 +/- 4.7 mmHg, P < 0.01; DBP, untreated: 87 +/- 3.0 mmHg versus ouabain-treated: 114 +/- 2.6 mmHg, P < 0.001). EFS-induced vasoconstrictions were smaller in arteries from ouabain-treated rats than in those from untreated animals, while the EFS-induced [H]noradrenaline release and the vasoconstriction induced by exogenous noradrenaline (1 nmol/l-10 micromol/l) remained unmodified. The non-selective NO synthase (NOS) inhibitor, N-nitro-L-arginine methyl ester (100 micromol/l), increased the EFS-induced vasoconstriction in mesenteric arteries from both groups, although the effect was more pronounced in segments from ouabain-treated rats. The selective neuronal NOS inhibitor, 7-nitroindazole (7-NI; 100 micromol/l) increased EFS-induced contraction only in segments from ouabain-treated rats. Neuronal NOS expression was greater in the mesenteric arteries from ouabain-treated rats than in those from untreated animals. Sodium nitroprusside (0.1 nmol/l-10 micromol/l) induced a similar vasodilatation in segments from both groups.. These results suggest that chronic ouabain treatment is accompanied by an increase in neuronal NO release that reduces EFS-induced vasoconstriction.

Topics: Animals; Electric Stimulation; Enzyme Inhibitors; Hypertension; Indazoles; Male; Mesenteric Arteries; Nitric Oxide Synthase; Nitric Oxide Synthase Type I; Nitroarginine; Ouabain; Rats; Rats, Wistar; Tritium; Vasoconstriction

The involvement of the superoxide anion in endothelium-dependent relaxation (EDR) was examined in noradrenaline-contracted aortic smooth muscle preparations isolated from normotensive Wistar Kyoto rats (WKY) and stroke-prone spontaneously hypertensive rats (SHRSP). Acetylcholine (ACh, 10(-9)-10(-5) M) induced EDR in both WKY and SHRSP preparations in a concentration-dependent manner, but with a significantly smaller amplitude in those from SHRSP than in those from WKY. The ACh-induced EDR was inhibited by N(omega)-nitro-L-arginine (L-NOARG), in a concentration-dependent manner, both in WKY and SHRSP. The EDR produced in WKY in the presence of 3 x 10(-6) M L-NOARG was similar in magnitude to that produced in SHRSP in the absence of L-NOARG. Superoxide dismutase (SOD, 300 units/ml) increased the amplitude of EDR in SHRSP but not in WKY, with no alteration of the threshold or of the maximal amplitude. The maximal amplitude of EDR produced in SHRSP in the presence of SOD was still smaller than that in WKY. In WKY, a possible involvement of superoxide in the EDR was examined in aortae whose EDR was partially inhibited by treatment with a subthreshold concentration (3 x 10 (-6) M) of L-NOARG. In the L-NOARG-conditioned aorta, the reduced EDR was partially but significantly recovered by SOD. These results suggest that the impaired EDR in aortae of SHRSP may be causally related to a higher production of superoxide. The L-NOARG-induced inhibition of EDR in WKY may be produced, in part, by the reduction of effective NO due to its destruction by superoxide.

Topics: Acetylcholine; Animals; Aorta; Blood Pressure; Body Weight; Endothelium, Vascular; Enzyme Inhibitors; Hypertension; Male; Muscle Relaxation; Muscle, Smooth, Vascular; Nitric Oxide; Nitroarginine; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Superoxide Dismutase

We reported previously that endothelium-intact superior mesenteric arteries (SMA) from N(omega)-nitro-L-arginine (L-NNA)-treated hypertensive rats (LHR) contract more to norepinephrine (NE) than SMA from control rats. Others have shown that nitric oxide (NO) synthase (NOS) inhibition increases cyclooxygenase (COX) function and expression. We hypothesized that augmented vascular sensitivity to NE in LHR arteries is caused by decreased NOS-induced dilation and increased COX product-induced constriction. We observed that the EC50 for NE is lower in LHR SMA compared with control SMA (control -6.37 +/- 0.04, LHR -7.89 +/- 0.09 log mol/l; P <0.05). Endothelium removal lowered the EC50 (control -7.95 +/- 0.11, LHR -8.44 +/- 0.13 log mol/l; P <0.05) and increased maximum tension in control (control 1,036 +/- 38 vs. 893 +/- 21 mg; P <0.05) but not LHR (928 +/- 30 vs. 1,066 +/- 31 mg) SMA. Thus augmented NE sensitivity in LHR SMA depends largely on decreased endothelial dilation. NOS inhibition (L-NNA, 10(-4) mol/l) increased maximum tension and EC50 in control arteries but not in LHR arteries. In contrast, COX inhibition decreased maximum tension in control arteries, suggesting that COX products augment contraction. Indomethacin did not affect NE-induced contraction in L-NNA-treated or denuded arteries. In control SMA loaded with the fluorescent NO indicator 4-amino-5-methylamino-2',7'-difluorofluorescein diacetate, indomethacin increased and L-NNA decreased NO release. Therefore, COX products appear to inhibit NO production to augment NE-induced contraction. With chronic NOS inhibition, this modulating influence is greatly diminished. Thus, in NOS-inhibition hypertension, decreased activity of both COX and NOS pathways profoundly disrupts endothelial modulation of contraction.

Topics: Adrenergic alpha-Agonists; Animals; Blotting, Western; Cyclooxygenase 1; Cyclooxygenase 2; Cyclooxygenase 2 Inhibitors; Cyclooxygenase Inhibitors; Endothelium, Vascular; Enzyme Inhibitors; Hypertension; Isoenzymes; Male; Membrane Proteins; Mesenteric Arteries; Muscle, Smooth, Vascular; Nitric Oxide Synthase; Nitroarginine; Nitrobenzenes; Norepinephrine; Prostaglandin-Endoperoxide Synthases; Rats; Rats, Sprague-Dawley; Salicylates; Sulfonamides; Vasoconstriction

PKC augments calcium sensitivity in spontaneously hypertensive rats and contributes to alpha(2)-adrenergic receptor (AR) contraction in rabbit saphenous vein. We showed previously that denuded aortic rings from N(omega)-nitro-l-arginine-treated hypertensive rats (LHR) contract more to CaCl(2) and to the alpha(2)-AR agonist UK-14304 than do rings from normotensive rats (NR). We hypothesized that enhanced PKC activity or a change in PKC isoform contributes to augmented calcium sensitivity and enhanced alpha(2)-AR contraction in LHR aorta. Current studies demonstrate that non-isoform-specific PKC inhibitors reduced UK-14304 contraction in both NR and LHR aorta. However, the calcium-dependent PKC inhibitor Gö-6976 only attenuated contraction in LHR aorta. Additionally, UK-14304 translocated PKC-delta to the membrane in NR aorta, whereas PKC-alpha was translocated to the membrane in LHR aorta. Finally, in ionomycin-permeabilized aorta Gö-6976 eliminated enhanced basal and augmented alpha(2)-AR-stimulated calcium sensitivity in LHR aorta but did not affect NR contraction. Together, these data suggest that PKC-alpha contributes to augmented calcium sensitivity and alpha(2)-AR reactivity after chronic nitric oxide synthase inhibition hypertension.

Topics: Animals; Aorta; Calcium; Chronic Disease; Hypertension; In Vitro Techniques; Male; Nitric Oxide Synthase; Nitroarginine; Protein Kinase C; Rats; Rats, Sprague-Dawley; Receptors, Adrenergic, alpha-2; Vasoconstriction; Vasomotor System

This study was designed to determine the effect of pteridines, R- and S-tetrahydrobiopterin, sepiapterin, and dihydrobiopterin on endothelium-dependent contractions to acetylcholine in isolated aortas from spontaneously hypertensive rat and normotensive Wistar-Kyoto rat. The noncumulative addition of redox-active pteridines R- and S-tetrahydrobiopterin (but not the oxidized analogues sepiapterin and dihydrobiopterin) produced a concentration-dependent transient contraction in isolated aortic rings from both normotensive and hypertensive rats. R- and S-tetrahydrobiopterin (but not sepiapterin or dihydrobiopterin) potentiated the endothelium-dependent contractions to acetylcholine but only in aortas from hypertensive rats and in the presence of N(G)-nitro-L-arginine. In these aortas, the generation of oxygen-derived free radicals by the combination of xanthine plus xanthine oxidase also potentiated the endothelium-dependent contractions to acetylcholine. The presence of R-tetrahydrobiopterin did not alter the characteristics of the endothelium-dependent contractions because they were inhibited by valeryl salicylate, an inhibitor of cyclooxygenase-1, by S18886, a TP-receptor antagonist or by Tiron, a cell permeable superoxide anion scavenger. However, the contractions to acetylcholine, which are unaffected by the combination of superoxide dismutase and catalase, become significantly inhibited by these two scavengers in the presence of R-tetrahydrobiopterin. In the presence of N(G)-nitro-L-arginine, R-tetrahydrobiopterin did not affect the contractions to phenylephrine, U 46619, or to oxygen-derived free radicals generated by xanthine plus xanthine oxidase. These results indicate that the production of superoxide by the autoxidation of tetrahydrobiopterin selectively enhances endothelium-dependent contractions in the spontaneously hypertensive rat when nitric oxide synthase is inhibited.

Topics: Acetylcholine; Animals; Aorta; Biopterins; Culture Techniques; Dithiothreitol; Dose-Response Relationship, Drug; Drug Synergism; Endothelium, Vascular; Enzyme Inhibitors; Hypertension; Nitric Oxide Synthase; Nitroarginine; Pteridines; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Reactive Oxygen Species; Reducing Agents; Vasoconstriction; Vasodilation

Periodic acceleration (pGz), a novel method of ventilatory support, is achieved using a platform that moves cyclically in the headward-footward direction. PGz has been shown to increase vascular shear stress and regional blood flows, as well as decrease pulmonary and systemic vascular resistances. PGz also increases nitric oxide (NO) production. This study was undertaken to determine the effects of pGz on the NO inhibiting effects of N-w-nitro-L-arginine (L-NAME) in vivo, and to determine if increased NO production due to pGz could be reproduced in vitro with isolated arteries. Pigs were assigned to conventional ventilation (CV), or pGz, with no additional breathing assistance. L-NAME was infused in cumulative doses of 1, 3, 10, 30, and 100 mg/kg. Cardiac output decreased in both groups by 50%. There was also a dose-dependent increase in blood pressure, pulmonary artery pressure, and vascular resistances. However, pGz attenuated the vascular response of L-NAME. Isolated porcine aortas exposed to nonpulsatile, pulsatile, and pulsatile flow plus pGz exhibited an increase in nitrites with the addition of pulsatile flow (300%, relative to steady flow), and a further increase with pGz (1000%, relative to steady flow). It has been determined that pGz, a novel method of increasing shear stress on the vascular endothelium. attenuates the vasoactive response to L-NAME. The in vitro experiments demonstrated that increases in NO production in vivo could be reproduced in vitro, which provides the opportunity to investigate the mechanisms of cardiovascular pGz effects.

Topics: Acceleration; Animals; Aorta; Cardiac Output; Dose-Response Relationship, Drug; Endothelium, Vascular; Hypertension; In Vitro Techniques; Nitric Oxide; Nitrites; Nitroarginine; Stress, Mechanical; Swine; Vascular Resistance; Vasoconstriction; Ventilators, Negative-Pressure

Both carbon monoxide (CO), the product of heme oxygenase (HO), and nitric oxide (NO) elevate cyclic guanosine monophosphate levels in smooth muscle cells, leading to relaxation of the vessels. We examined the hypothesis that the effect of CO in regulating blood pressure could be augmented in hypertension where the function and/or production of NO is impaired. We used two hypertensive models, a spontaneously hypertensive rat (SHR), and a Wistar Kyoto rat (WKY) which was given the NO synthase (NOS) inhibitor N(omega)-nitro- L-arginine (L-NNA). In these hypertensive rats, we examined HO gene expression with Northern blot analysis, guanosine 3',5'-monophosphate (cGMP) levels with enzyme-linked immunosorbent assay of each organ, and the response of blood pressure to treatment with an HO substrate (hemin, 23 micromol/kg body weight, i.p.) or HO inhibitor (zinc or tin protoporphyrin-IX; ZnPP or SnPP, 50 micromol/kg body weight i.p. or s.c.), for 4 or 8 consecutive days with plethysmography. Northern blot analysis showed that HO-1 and -2 mRNA levels in the left ventricle, aorta, kidney, and soleus muscle in the hypertensive rats were 2-5 times higher than those in control normotensive WKYrats. In contrast, both HO mRNA levels in the gastrocnemius muscle in the hypertensive rats were similar to those in control WKYrats. As to whether the HO/CO system contributes to the regulation of blood pressure, ZnPP or SnPP increased and hemin decreased systolic blood pressure (SBP), respectively, in the hypertensive rats (P < 0.01), but not in WKYrats, accompanied with changes in cGMP in each organ of the hypertensive rats. The effect of CO in the regulation of blood pressure is augmented, resulting in increased expression of HO gene when the function and/or production of NO is impaired.

Topics: Animals; Aorta; Blood Pressure; Blotting, Northern; Carbon Monoxide; Cyclic GMP; Enzyme Inhibitors; Heme Oxygenase (Decyclizing); Hemin; Hypertension; Kidney; Male; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Protoporphyrins; Rats; Rats, Inbred SHR; Rats, Inbred WKY; RNA, Messenger

Arteries from deoxycorticosterone acetate (DOCA)-salt and N(omega)-nitro-L-arginine (L-NNA) hypertensive but not normotensive rats develop spontaneous tone. LY294002 and wortmannin, phosphoinositide 3-kinase (PI3-kinase) inhibitors, eliminate spontaneous tone. We hypothesized that PI3-kinase protein and/or activity was increased in hypertension and contributed to the observed enhanced contractility. PI3-kinase activity assays revealed 2-fold higher activity in thoracic aorta from DOCA-salt [systolic blood pressure (SBP)=184+/-5 mm Hg] compared with sham rats (SBP=111+/-2 mm Hg). Western analyses of aortic homogenates revealed the presence of p85alpha, p110alpha, p110beta, and p110delta but not p110gamma PI3-kinase subunits; p110delta protein was elevated in aorta of hypertensive rats as compared with sham. Aortic homogenates from L-NNA rats also had elevated p110beta protein density, but neither L-NNA nor DOCA-salt had differences in p85alpha and p110alpha. Total Akt density was unaltered, but pAkt was significantly lower in homogenates from DOCA-salt rats. LY294002 (20 micromol/L) and nifedipine (50 nmol/L) abolished Ca2+-induced spontaneous tone in aorta from DOCA-salt rats. However, LY294002 did not alter BayK8644-induced contraction, indicating that LY294002 does not inhibit L-type Ca2+ channels directly. PTEN (phosphatase and tensin homolog) and pPTEN were expressed but not different in aorta from DOCA-salt and sham rats. LY294002 corrected the enhanced contraction to KCl and norepinephrine in aorta from DOCA-salt rats. These data support an increase in PI3-kinase activity and p110delta density in aorta from L-NNA and DOCA-salt rats. Importantly, this increase contributes to the enhanced contractility observed in two models of hypertension.

Topics: Animals; Aorta, Thoracic; Blotting, Western; Calcium; Calcium Channel Agonists; Calcium Channel Blockers; Desoxycorticosterone; Disease Models, Animal; Enzyme Activation; Enzyme Inhibitors; Hypertension; In Vitro Techniques; Male; Nitroarginine; Phosphatidylinositol 3-Kinases; Phosphoinositide-3 Kinase Inhibitors; Phosphoric Monoester Hydrolases; Protein Serine-Threonine Kinases; Protein Subunits; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-akt; PTEN Phosphohydrolase; Rats; Rats, Sprague-Dawley; Tumor Suppressor Proteins; Vasoconstriction; Vasoconstrictor Agents

To explore the changes in adrenomedullin (ADM) and receptor activity-modifying protein 2 (RAMP2) mRNA in myocardium and vessels in hypertension, a hypertensive rat model was prepared by administering L-NNA. Contents of ADM in plasma, myocardium and vessels were measured by radioimmunoassay (RIA). The levels of pro-ADM mRNA of myocardium and vessels were determined by competitive quantitative RT-PCR. The results showed that L-NNA induced hypertension and cardiomegaly. The ratio of heart to body weight increased by 35.5% (P<0.01). In hypertensive rats the ir-ADM in plasma, myocardium and vessels was increased by 80%, 72% and 57% (P<0.01), respectively compared with the control. The amounts of ADM mRNA in myocardium and vessels were increased by 50% and 109.2% (P<0.05), respectively, and the amounts of RAMP2 mRNA was increased by 132% and 87% (P<0.01), respectively, compared with control. The levels of ADM in myocardium and vessels were positively correlated with RAMP2 mRNA, the correlation coefficients were 0.741 and 0.885 (P<0.01), respectively. The results obtained indicate that in hypertensive rats, ADM is elevated in plasma, myocardium and ves-myocardium and vessel, and ADM and RAMP2 mRNA are up-regulated in myocardium and vessel. The ADM/RAMP2 system may play an important role in the pathogenesis of hypertension.

Topics: Adrenomedullin; Animals; Cardiomegaly; Hypertension; Myocardium; Nitroarginine; Rats; Receptor Activity-Modifying Protein 2; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Up-Regulation

1. The direct and endothelium-dependent effects of lipopolysaccharide (LPS) were investigated on resistance and conductance arteries from normotensive Wistar (NWR) and spontaneously hypertensive (SHR) rats. 2. In both NWR and SHR, LPS induced dose-dependent relaxations of the mesenteric vascular bed, which were inhibited by L-NNA in SHR but not in NWR. Iberiotoxin (IBTX) inhibited the responses to LPS in both groups, indicating the participation of high conductance Ca(2+)-dependent K(+) channels. 3. In mesenteric artery rings, the resting membrane potentials and the hyperpolarizing responses of NWR to LPS did not differ in endothelized and denuded preparations but L-NNA inhibited the responses only in endothelized rings. These responses were reduced by bosentan, suggesting that endothelin release may mask a possible hyperpolarizing response to LPS. The hyperpolarizing responses to LPS were blocked by IBTX in both endothelized and de-endothelized NWR rings. In the SHR only intact rings showed hyperpolarization to LPS, which was inhibited by IBTX and byL-NNA. 4. In SHR aortic endothelized or denuded rings, LPS induced hyperpolarizing responses which, in endothelized rings, were partially blocked by L-NNA, by IBTX or by glibenclamide, but totally abolished by IBTX plus glibenclamide. No response to LPS was observed in NWR aortic rings. 5. Our results indicate that LPS activates large conductance Ca(2+)-sensitive K(+) channels located in the smooth muscle cell membrane both directly and indirectly, through NO release from the endothelium in NWR, whereas NO is the major mediator of the LPS responses in SHR resistance vessels.

Topics: Animals; Aorta, Thoracic; Arteries; Dose-Response Relationship, Drug; Hypertension; In Vitro Techniques; Lipopolysaccharides; Male; Membrane Potentials; Mesenteric Arteries; Nitric Oxide; Nitroarginine; Peptides; Potassium Channels; Rats; Rats, Inbred SHR; Rats, Wistar; Vasodilation

We demonstrated that arteries from rats made hypertensive with chronic nitric oxide (NO) synthase (NOS) inhibition (N(omega)-nitro-L-arginine in drinking water, LHR) have enhanced contractile sensitivity to alpha(2)-adrenergic receptors (alpha(2)-AR) agonist UK-14304 compared with arteries from normotensive rats (NR). NO may regulate vascular tone in part through suppression of RhoA and Rho kinase (ROK). We hypothesized that enhanced RhoA and ROK activity augments alpha(2)-AR contraction in LHR aortic rings. Y-27632 eliminated UK-14304 contraction in LHR and NR aortic rings. The order of increasing sensitivity to Y-27632 was the following: endothelium-intact NR, LHR, and endothelium-denuded NR. UK-14304 stimulated RhoA translocation to the membrane fraction in LHR and denuded NR but not in intact NR aorta. Basally, more RhoA was present in the membrane fraction in denuded NR than in intact NR or LHR aorta. Relaxation to S-nitroso-N-acetyl-penicillamine and Y-27632 in denuded ionomycin-permeabilized rings was greater in NR than in LHR. Together these studies indicate alpha(2)-AR contraction depends on ROK activity more in NR than LHR aorta. Additionally, endogenous NO may regulate RhoA activation, whereas chronic NOS inhibition appears to cause RhoA desensitization.

Topics: Adrenergic alpha-Agonists; Amides; Animals; Aorta; Brimonidine Tartrate; Enzyme Inhibitors; Hypertension; Intracellular Signaling Peptides and Proteins; Male; Muscle, Smooth, Vascular; Nitric Oxide Donors; Nitric Oxide Synthase; Nitroarginine; Penicillamine; Protein Serine-Threonine Kinases; Pyridines; Quinoxalines; Rats; Rats, Sprague-Dawley; Receptors, Adrenergic, alpha-2; rho-Associated Kinases; rhoA GTP-Binding Protein; Vasoconstriction

Arterial hyperresponsiveness to serotonin (5-hydroxytryptamine, 5-HT) is observed in experimental models and human forms of hypertension. Presently, we test the hypothesis that the 5-HT(2B) receptor is up-regulated and necessary for maintaining elevated blood pressure in a rat made hypertensive by the nitric-oxide synthase inhibitor N(omega)-nitro-L-arginine (LNNA; 0.5 g/l). After 2 weeks of treatment, thoracic aorta were removed from LNNA hypertensive (systolic blood pressure = 189 +/- 5 mm Hg) and sham normotensive rats (121 +/- 1 mm Hg), denuded, and mounted into isolated tissue baths for measurement of isometric contraction. In sham tissues, 5-HT-induced contraction was mediated by the 5-HT(2A) receptor as evidence by a parallel rightward shift in response to 5-HT by the 5-HT(2A/2C) receptor antagonist ketanserin (10 nM) and lack of shift by the 5-HT(2B) receptor antagonist 6-methyl-1,2,3,4-tetrahydro-1-[3,4-dimethoxyphenyl)methyl]-9H-pyrido[3,4-b]indole hydrochloride (LY272015) (10 nM). In contrast, LY272015 produced a 4-fold rightward shift to 5-HT in aorta from LNNA hypertensive rats, and blockade by ketanserin did not occur at low concentrations of 5-HT. Maximal contraction to the 5-HT(2B) receptor agonist 1-[5-(2-thienylmethoxy)-1H-3-indolyl]propan-2-amine hydrochloride was significantly greater in LNNA hypertensive rats (percentage of phenylephrine contraction in sham = 7 +/- 4, and in LNNA = 61 +/- 7%). 5-HT(2B) receptor protein was present in aortic homogenates from sham and LNNA rats, but the density of 5-HT(2B) receptor protein in LNNA homogenates was 300% that in sham. Importantly, the 5-HT(2B) receptor antagonist LY272015 reduced blood pressure of the LNNA hypertensive but not the sham normotensive rats. Thus, these data suggest that the up-regulated 5-HT(2B) receptor in the LNNA hypertensive rats is physiologically activated to maintain elevated blood pressure.

Topics: Animals; Antihypertensive Agents; Aorta, Thoracic; Disease Models, Animal; Endothelium, Vascular; Humans; Hypertension; In Vitro Techniques; Ketanserin; Male; Nitroarginine; Organic Chemicals; Rats; Rats, Sprague-Dawley; Receptor, Serotonin, 5-HT2B; Receptors, Serotonin; Serotonin; Serotonin Receptor Agonists; Vasoconstriction

The aim of this work was to investigate the mechanism of the vasodilatory effect induced by L-carnitine. Relaxation produced by L-carnitine was studied in rat aortic rings with and without functional endothelium, pre-contracted with phenylephrine by adding cumulative doses of L-carnitine (10(-7) to 10(-3) M). The relaxation evoked by L-carnitine reached higher values in aortic rings from spontaneously hypertensive rats than those obtained in arteries from normotensive rats; no relaxation was produced in de-endothelialized arteries. However, in the presence of N(G)-nitro-L-arginine (3 x 10(-5) M, a nitric oxide synthase inhibitor), Ro 68070 (10(-4) M, a thromboxane synthetase inhibitor-thromboxane A2/prostaglandin H2 receptor antagonist) or ICI 192605 (10(-5) M, a thromboxane A2 receptor antagonist) the relaxant response to L-carnitine was significantly inhibited. These results show that L-carnitine induced endothelium-dependent relaxation in the rat aorta and the mechanism of this relaxation appeared to be mostly mediated by endothelial production of nitric oxide but#10; also could involve prevention of the action of cyclooxygenase endothelial products acting on the thromboxane A2/prostaglandin H2 receptor.

Topics: Animals; Aorta, Thoracic; Carnitine; Dioxanes; Endothelium, Vascular; Enzyme Inhibitors; Hypertension; In Vitro Techniques; Male; Muscle Relaxation; Muscle, Smooth, Vascular; Nitric Oxide Synthase; Nitric Oxide Synthase Type III; Nitroarginine; Prostaglandin Antagonists; Prostaglandins; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Thromboxane-A Synthase; Vasodilation

An imbalance between production of reactive oxygen species (ROS) and antioxidant defense is involved in the pathogenesis of diverse chronic parenchymatous diseases. To identify the primary site of such increased oxidative stress, a lipophilic ROS-sensitive probe (C11-Bodipy 581/591) is introduced, which allows the visualization and quantification of oxidative injury using confocal fluorescence microscopy in living cells. The properties of this probe are such that its emission wavelength irreversibly shifts from red to green upon oxidation. This probe was used to identify the spatiotemporal distribution of lipid peroxidation in the rat kidney during chronic NOS inhibition, a model associated with hypertension and proteinuria. Chronic NOS inhibition resulted in increased lipid peroxidation in renal tubules but hardly any in glomeruli or blood vessels. This peroxidation preceded the loss of renal function characteristic of the model and was accompanied by parallel changes in thiobarbituric acid reactive substances in the renal cortex. Furthermore, the increase in oxidation was dependent on angiotensin II and NADPH oxidase and prevented by vitamin E. Induction of cytoprotective heat-shock protein 70 preceded lipid peroxidation, rise in BP, or proteinuria. These findings challenge the paradigm that the vascular wall is the source and target of oxidative stress in chronic parenchymatous renal disease associated with hypertension.

Topics: Angiotensin II; Animals; Antioxidants; Enzyme Inhibitors; HSP70 Heat-Shock Proteins; Hypertension; Kidney; Kidney Tubules; Lipid Peroxidation; Male; NADPH Oxidases; Nitric Oxide Synthase; Nitroarginine; Oxidative Stress; Rats; Rats, Sprague-Dawley; Vitamin E

To evaluate whether the elevated blood pressure induced by chronic treatment with N(omega)-nitro-L-arginine methyl ester (L-NAME) contributes to an impairment of endothelium-dependent relaxation (EDR), the effects of chronic treatment of Wistar rats with L-NAME on systolic blood pressure, pulmonary arterial blood pressure and EDR of the pulmonary arteries were studied and compared with those of stroke-prone spontaneously hypertensive rats (SHRSP). While the systolic blood pressure (SBP) of Wistar rats was increased above that of controls by chronic treatment with L-NAME, it was still significantly lower than that of SHRSP. Chronic treatment with L-NAME did not affect pulmonary arterial blood pressure. On the other hand, the pulmonary arterial blood pressure of SHRSP was slightly but significantly higher than that of the control normotensive Wistar Kyoto rats (WKY). EDR in response to acetylcholine in the pulmonary artery of L-NAME-treated rats was significantly smaller than that in control Wistar rats. The EDR markedly increased in the presence of L-arginine and completely disappeared in the presence of N(omega)-nitro-L-arginine. Indomethacin hardly affected EDR. In preparations from SHRSP, the EDR was not different from that in those from WKY. Relaxation induced by sodium nitroprusside was identical in all preparations. Elevation of SBP and the impairment of EDR observed in L-NAME-treated rats recovered two weeks following cessation of treatment. These results suggest that the impaired EDR in the pulmonary artery of L-NAME-treated rats is not due to an L-NAME-induced increase in blood pressure but due to the inhibition of nitric oxide synthase by the drug remaining in the endothelium.

Topics: Animals; Arginine; Blood Pressure; Body Weight; Cardiovascular Agents; Endothelium, Vascular; Enzyme Inhibitors; Genetic Predisposition to Disease; Hypertension; Indomethacin; Male; NG-Nitroarginine Methyl Ester; Nitric Oxide Donors; Nitroarginine; Nitroprusside; Pulmonary Artery; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Rats, Wistar; Stroke; Vasodilation

We hypothesized that altered vasoreactivity in perinatal pulmonary hypertension (PH) is characterized by abnormal responses to hemodynamic stress, including the loss of flow-induced vasodilation and an augmented myogenic response. Therefore, we studied the acute hemodynamic effects of brief compression of the ductus arteriosus (DA) in control fetal lambs and in lambs during exposure to chronic PH. In both groups, acute DA compression decreased pulmonary vascular resistance (PVR) by 20% at baseline (day 0). After 2 days of hypertension, acute DA compression paradoxically increased PVR by 50% in PH lambs, whereas PVR decreased by 25% in controls. During the 8-day study period, PVR increased during acute DA compression in PH lambs, whereas acute DA compression continued to cause vasodilation in controls. Brief treatment with the nitric oxide (NO) synthase inhibitor nitro-L-arginine (L-NA) increased basal PVR in control but not PH lambs, suggesting decreased NO production in PH lambs. Chronic hypertension increased the myogenic response after L-NA in PH lambs, whereas the myogenic response remained unchanged in controls. The myogenic response was inhibited by nifedipine in PH lambs, suggesting that the myogenic response is dependent upon the influx of extracellular calcium. We conclude that chronic PH impairs flow-induced vasodilation and increases the myogenic response in fetal lung. We speculate that decreased NO signaling and an augmented myogenic response contributes to abnormal vasoreactivity in PH.

Topics: Animals; Calcium Channel Blockers; Calcium Channels; Chronic Disease; Ductus Arteriosus; Enzyme Inhibitors; Hypertension; Lung; Muscle, Smooth, Vascular; Nifedipine; Nitric Oxide Synthase; Nitroarginine; Pressure; Pulmonary Circulation; Reference Values; Sheep; Time Factors; Vasodilation; Vasomotor System

Blood vessels express estrogen receptors, but their role in cardiovascular physiology is not well understood. We show that vascular smooth muscle cells and blood vessels from estrogen receptor beta (ERbeta)-deficient mice exhibit multiple functional abnormalities. In wild-type mouse blood vessels, estrogen attenuates vasoconstriction by an ERbeta-mediated increase in inducible nitric oxide synthase expression. In contrast, estrogen augments vasoconstriction in blood vessels from ERbeta-deficient mice. Vascular smooth muscle cells isolated from ERbeta-deficient mice show multiple abnormalities of ion channel function. Furthermore, ERbeta-deficient mice develop sustained systolic and diastolic hypertension as they age. These data support an essential role for ERbeta in the regulation of vascular function and blood pressure.

Topics: Adrenergic alpha-Agonists; Animals; Aorta; Blood Pressure; Cells, Cultured; Estradiol; Estrogen Antagonists; Estrogen Receptor alpha; Estrogen Receptor beta; Fulvestrant; Guanidines; Humans; Hypertension; In Vitro Techniques; Male; Mice; Mice, Knockout; Muscle, Smooth, Vascular; Nitric Oxide Synthase; Nitric Oxide Synthase Type II; Nitroarginine; Patch-Clamp Techniques; Phenylephrine; Potassium Channels; Receptors, Estrogen; Vasoconstriction

To evaluate the effect of EDDF a new erythrocyte-derived depressing factor, on the NO/cGMP pathway in aorta of normal rats and rat, with hypertension induced by L-NNA.. Thirty male Wistar rats aged 10 weeks were divided into two groups: L-NNA group and control group, 15 rats for each group. L-N(G)-nitro-arginine (L-NNA) was injected into the abdominal cavity of the rats in the L-NNA group at dose of 15 mg/kg twice a day for four weeks. Normal saline was injected the same way in the control group. The levels of cGMP in aorta and plasma were measured by radioimmunoassay and (3)H-L-arg incorporation. NOS was measured by immunohistochemistry.. One day after injection of L-arg, the blood pressure of the experimental rats began to rise remarkably (18.8 kPa vs 16.4 kPa, P < 0.05), and then remained at a high level. The L-arg. transfer rate (pmol small middle dotmg(-1) small middle dotpr small middle dotmin(-1)) of aorta in L-NNA group was significantly lower than that of control group (13.0 +/- 0.9 vs 16.8 +/- 1.2 P < 0.05). After incubation with EDDF (10(-4) g/ml), the L-arg transfer rate and cGMP level of aorta were remarkably increased in normal rats (20.1 +/- 0.9 vs 16.8 +/- 1.2, P < 0.05 and 233 +/- 14 vs 187 +/- 10, P < 0.05). The L-arg transfer rate and cGMP level of aorta remained unchanged afeter incubation with EDDF in the L-NNA group (13.0 +/- 0.9 vs 13.2 +/- 0.3 and 148 +/- 16 vs 186 +/- 12). The cGMP level (pmol/g) of aorta in L-NNA group were obviously lower than that of control rats (148 +/- 16 vs 186 +/- 12, P < 0.05). Immunohistological staining of NOS in aorta was obviously lighter in L-NNA group than in control group. The immunohistochemical staining intensity in aorta remained the same after incubation with EDDF in L-NNA group.. The NO/cGMP pathway might be in charge of vasodilation mechanism of EDDF.

Topics: Animals; Aorta; Blood Proteins; Cyclic GMP; Disease Models, Animal; Humans; Hypertension; Male; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Rats; Rats, Wistar; Vasodilation

Nitric oxide (NO) synthase (NOS) inhibition with N(omega)-nitro-L-arginine (L-NNA) produces L-NNA hypertensive rats (LHR), which exhibit increased sensitivity to voltage-dependent Ca(2+) channel-mediated vasoconstriction. We hypothesized that enhanced contractile responsiveness after NOS inhibition is mediated by depolarization of membrane potential (E(m)) through attenuated K(+) channel conductance. E(m) measurements demonstrated that LHR vascular smooth muscle cells (VSMCs) are depolarized in open, nonpressurized (-44.5 +/- 1.0 mV in control vs. -36.8 +/- 0.8 mV in LHR) and pressurized mesenteric artery segments (-41.8 +/- 1.0 mV in control vs. -32.6 +/- 1.4 mV in LHR). Endothelium removal or exogenous L-NNA depolarized control VSMCs but not LHR VSMCs. Superfused L-arginine hyperpolarized VSMCs from both the control and LHR groups and reversed L-NNA-induced depolarization (-44.5 +/- 1.0 vs. -45.8 +/- 2.1 mV). A Ca(2+)-activated K(+) channel agonist, NS-1619 (10 microM), hyperpolarized both groups of arteries to a similar extent (from -50.8 +/- 1.0 to -62.5 +/- 1.2 mV in control and from -43.7 +/- 1.1 to -55.6 +/- 1.2 mV in LHR), although E(m) was still different in the presence of NS-1619. In addition, superfused iberiotoxin (50 nM) depolarized both groups similarly. Increasing the extracellular K(+) concentration from 1.2 to 45 mM depolarized E(m), as predicted by the Goldman-Hodgkin-Katz equation. These data support the hypothesis that loss of NO activation of K(+) channels contributes to VSMC depolarization in L-NNA-induced hypertension without a change in the number of functional large conductance Ca(2+)-activated K(+) channels.

Topics: Animals; Arginine; Benzimidazoles; Calcium; Cell Membrane; Endothelium, Vascular; Enzyme Inhibitors; Hypertension; Male; Membrane Potentials; Mesenteric Arteries; Muscle, Smooth, Vascular; Nitric Oxide Donors; Nitric Oxide Synthase; Nitroarginine; Penicillamine; Peptides; Potassium; Potassium Channel Blockers; Potassium Channels; Rats; Rats, Sprague-Dawley

Arterial hypertension (AH) is characterized by reduced nitric oxide (NO) biosynthesis, vasoconstriction, and reduced microvascular density. In this study we asked whether AH also reduces the number of microvessels by impairing angiogenesis. AH was induced in Dahl salt-sensitive rats (DSS) with a salt diet and in Wistar-Kyoto rats by inhibiting NO formation with Nomega-nitro-L-arginine (NNA). Three weeks after induction of AH, two wound chambers containing collagen I (Vitrogen) were sutured into the mesenteric cavity of each animal. After additional 14 days, wound chamber neovascularization and the extent of vascularized connective tissue ingrowth were quantified. In NNA-induced AH, the number of newly formed vessels and the ingrowth of vascularized connective tissue into the wound chamber decreased as compared to controls. However, the number of newly formed vessels and the ingrowth of vascularized connective tissue did not change with increasing blood pressure in salt-fed DSS rats as compared to those fed a normal diet. Inhibition of NO biosynthesis, but not necessarily elevating blood pressure, reduces angiogenesis. Microvascular rarefaction in AH may be partially due to reduced angiogenesis because of impaired NO biosynthesis.

Topics: Animals; Blood Pressure; Disease Models, Animal; Hypertension; Neovascularization, Pathologic; Nitric Oxide; Nitroarginine; Rats; Rats, Inbred Dahl; Rats, Inbred WKY; Sodium Chloride

Rats were made hypertensive by the administration of the nitric oxide synthase inhibitor nitro-L-arginine (LNA, 2.74 mmol/L) in drinking water for 7 d. Hearts from hemodynamically assessed animals were analyzed for lipid peroxidation (LPO), gamma-glutamylcysteine-synthetase (gamma-GCS), glutathione disulfide reductase (GR), glutathione peroxidase (GSHPx), catalase (CAT), superoxide dismutase (SOD), and total radical trapping potential (TRAP) activities. LNA treatment increased the mean arterial blood pressure by 46% and the heart rate by 22% without changing plasma renin activity. LNA treatment resulted in a 30% increase in LPO. gamma-GCS was reduced by 48% and GR by 36% in the cardiac tissue of hypertensive rats as compared to controls. The activity of nonselenium GSHPx was reduced by 27%, and selenium-dependent GSHPx activity in the heart was not affected by LNA treatment. In hypertensive rats, SOD activity was increased by 16%, and CAT was decreased by 46%. TRAP was lower (27%) in the myocardium of hypertensive rats than in that of controls. These data suggest that LNA-induced hypertension is associated with increased myocardial oxidative stress.

Topics: Animals; Antioxidants; Catalase; Enzyme Inhibitors; Glutamate-Cysteine Ligase; Glutathione; Glutathione Peroxidase; Glutathione Reductase; Heart; Hypertension; Male; Myocardium; Nitric Oxide Synthase; Nitroarginine; Oxidative Stress; Rats; Rats, Wistar; Renin; Superoxide Dismutase

Chronic nitric oxide (NO) synthase (NOS) inhibition results in renal injury. Hypertension is an important risk factor for renal injury. We studied the influence of preexistent hypertension on the sensitivity for renal injury induced by chronic NOS inhibition in rats. Spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) rats were treated with 3, 10, 30 and 100 mg/l Nomega-nitro-L-arginine (L-NNA) until death. Systolic blood pressure and proteinuria were measured regularly and compared with time-control measurements in untreated SHR and WKY. In WKY, 3 and 10 mg/l L-NNA did not affect systolic blood pressure, while 30 and 100 mg/l L-NNA resulted in an increase in systolic blood pressure after 12 and 4 weeks, respectively. In contrast in SHR, every dose of L-NNA resulted in an increase in systolic blood pressure after 2 weeks. In WKY, 3 and 10 mg/l L-NNA did not affect proteinuria or survival, while 30 and 100 mg/l L-NNA resulted in an increase in proteinuria after 30 and 9 weeks, and a median survival of 36 and 12 weeks, respectively. In SHR, 3, 10, 30 and 100 mg/l L-NNA resulted in an increase in proteinuria after 30, 12, 3 and 3 weeks, and a median survival of 41, 20, 5 and 3 weeks, respectively. Thus, at every dose of the inhibitor, chronic NOS inhibition resulted in far earlier increases in systolic blood pressure and proteinuria and a marked increase in mortality in SHR as compared to WKY. Indeed, a very low dosage of L-NNA that caused no harm in WKY was followed by marked increases in proteinuria and blood pressure and decreased survival in SHR. Hypertension strongly increases the vulnerability to cardiovascular risk factors that compromise the NO-system.

Topics: Animals; Blood Pressure; Dose-Response Relationship, Drug; Enzyme Inhibitors; Genetic Predisposition to Disease; Hypertension; Kidney; Male; Nitric Oxide Synthase; Nitroarginine; Proteinuria; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Survival Analysis; Systole; Time Factors

The vasodilatory effect of VEGF has not been characterized in the setting of hypertension. This study investigated the in vitro vasorelaxant effects of VEGF in organ chambers in the aorta of the adult (12-week-old) spontaneously hypertensive rats (SHR), young (4-week-old) SHR without hypertension, and age-matched Wistar-Kyoto (WKY) rats compared with acetylcholine (ACh). Cumulative concentration-relaxation curves were established for VEGF (approximately 10(-12)-10(-8.5) M) and ACh (approximately 10(-10)-10(-5) M) in U46619 (10(-8) M)-induced contraction. VEGF induced endothelium-dependent relaxation that was significantly reduced in the adult SHR compared with the age-matched WKY control (87.8 +/- 2.8 versus 61.4 +/- 8.6%, P = 0.01). These responses were significantly attenuated by pretreatment with N(omega)-nitro-L-arginine (L-NNA, 300 microM) alone (SHR: 25.1 +/- 1.9%; WKY: 21.0 +/- 2.6%; P = 0.01) or indomethacin (7 microM) + L-NNA (SHR: 30.2 +/- 2.1%; WKY: 35.0 +/- 2.9%; P = 0.01). Further addition of oxyhemoglobin (20 microM) abolished the residual relaxation and reduced the relaxation induced by nitroglycerin. ACh induced similar responses to VEGF. In contrast, pretreatment with indomethacin alone enhanced VEGF- or ACh-induced relaxations and the effect was greater in the adult SHR than in WKY rats. In contrast to the adult SHR versus WKY rats, there were no significant differences of VEGF- or ACh-induced relaxations between young SHR and WKY rats. The results demonstrate that VEGF induces endothelium- or nitric oxide-dependent relaxation, which is blunted in the adult SHR. The mechanism of this impairment may be related to decreased release of NO although increased release of contracting factors from the dysfunctional endothelium may also be involved.

Topics: Acetylcholine; Animals; Anti-Inflammatory Agents, Non-Steroidal; Blood Pressure; Endothelial Growth Factors; Endothelium, Vascular; Enzyme Inhibitors; Hypertension; In Vitro Techniques; Indomethacin; Lymphokines; Male; Muscle Relaxation; Muscle, Smooth, Vascular; Nitroarginine; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Vascular Endothelial Growth Factor A; Vascular Endothelial Growth Factors

To determine the effects on pre- and post-glomerular vascular resistance of adrenocorticotrophin (ACTH)-induced hypertension in rats, before and after blockade of nitric oxide formation.. Four groups of Sprague-Dawley rats were studied. Measurements were made in ACTH- (Synacthen Depot, 0.25 mg/kg twice daily for 8 days) and sham-treated anaesthetized rats, before and after either Nomega-nitro-L-arginine (L-NNA, 6 mg/kg) or vehicle.. Whole-kidney and single-nephron haemodynamics and function were measured. Glomerular capillary pressure was estimated from tubular stop-flow pressure measurements.. Blood pressure (P < 0.001), renal blood flow (RBF, P < 0.05) and glomerular filtration rate (P < 0.01) were increased following ACTH treatment compared with sham. There were no differences in either total renal, or pre- or post-glomerular vascular resistances, but stop-flow-estimated glomerular capillary pressure was elevated (P < 0.001) as was single-nephron glomerular filtration rate (SNGFR) (P < 0.001) and single-nephron blood flow (P < 0.01 ) in the ACTH- compared to the sham-treated rats. L-NNA treatment increased blood pressure by a similar extent in both ACTH- and sham-treated rats, but reduced RBF (P < 0.05) and glomerular filtration rate (GFR) (P < 0.05) more in the ACTH group; similar changes were seen in single-nephron values. L-NNA increased pre- and post-glomerular resistances to a greater extent in the ACTH group.. ACTH-induced hypertension produced glomerular hypertension and hyperfiltration, which may be due to nitric oxide-related vasodilatation of the renal vasculature.

Topics: Adrenocorticotropic Hormone; Animals; Glomerular Filtration Rate; Hemodynamics; Hypertension; Kidney Glomerulus; Male; Nitric Oxide; Nitroarginine; Rats; Rats, Sprague-Dawley

To elucidate the role of nitric oxide (NO) and renin-angiotensin system (RAS) in the development of salt-sensitive hypertension, we investigated the pressor responses and renal histologic changes after long-term inhibition of endogenous NO synthesis in Dahl-Iwai salt-sensitive (DS) and salt-resistant (DR) rats under salt-re-stricted conditions that exaggerate RAS activation. Male DS and DR rats (6 weeks old) were fed with a low-salt (0.3%) diet for 5 weeks. NG-nitro-L-arginine (L-NA; dissolved in 60 mg/L deionized water), an arginine analogue acting as a NO-inhibitor, was also administered for 5 weeks. L-NA administration induced a gradual increase in systolic blood pressure (SBP) in both strains, and the pressor response in DS rats was apparently more enhanced relative to that in DR rats. Urinary nitrate plus nitrite (u-NOx) excretion was decreased by L-NA, with a significant negative correlation between SBP and u-NOx excretion in DS rats but not in DR rats. Plasma renin activity and urinary aldosterone level were significantly increased in L-NA-treated DS rats on week 5. Marked histologic changes with glomerular sclerosis and increased proteinuria and urinary N-acetyl-beta-glucosaminidase excretion were found in L-NA-treated DS rats but not DR rats. Competitive RT-PCR of mRNA extracted from the glomeruli revealed that angiotensin II type 1 receptor (AT1R) mRNA level was significantly lower in DS rats than in DR rats at week 2, and that L-NA administration significantly reduced glomerular AT1R level of DS rats at week 5, possibly because of downregulation. Our results showed that, even under sodium restriction, the pressor response and renal injury induced by chronic NO inhibition were markedly more enhanced in DS rats than in DR rats, which indicates that depletion of NO participates in both the development of hypertension and glomerular injury in DS rats through a potential activation of RAS irrespective of sodium loading. These data suggest that endogenous NO is an essential determinant of salt-sensitive hypertension in DS rats.

Topics: Aldosterone; Animals; Blood Pressure; Diet, Sodium-Restricted; Down-Regulation; Glucuronidase; Hypertension; Kidney Glomerulus; Male; Nitrates; Nitric Oxide; Nitrites; Nitroarginine; Proteinuria; Rats; Rats, Inbred Dahl; Receptor, Angiotensin, Type 1; Receptor, Angiotensin, Type 2; Receptors, Angiotensin; Renin; Renin-Angiotensin System; RNA, Messenger; Sclerosis

The time course of the response to prolonged application of acetylcholine in mesenteric arteries from stroke-prone spontaneously hypertensive rats (SHRSP) and Wistar Kyoto rats (WKY) was compared. Only a relaxing response, which was blocked by N(omega)-nitro-L-arginine (L-NOARG), was observed after the prolonged application of a low concentration of acetylcholine (10(-8) M) in both preparations; the response was impaired in SHRSP preparations. Prolonged application of a high concentration of acetylcholine (10(-5) M) induced a second contractile response after a first relaxing response in SHRSP preparations under basal conditions and in WKY preparations in the presence of L-NOARG. This contractile response was attenuated by indomethacin. In the presence of a combination of apamin and charybdotoxin, the relaxing response to the high concentration of acetylcholine was reduced and a contractile response, which was abolished by indomethacin, appeared. In the presence of all of these blockers, a contractile response, which was blocked by cyclo(D-alpha-aspartyl-L-propyl-D-valyl-L-leucyl-D-tryptophyl) (BQ-123), was observed in preparations from WKY but not in preparations from SHRSP. Results indicate that prolonged application of acetylcholine in rat mesenteric arteries induces the release of endothelium-derived relaxing, contracting, hyperpolarizing factors and endothelin-1, and that the mode of action differs between preparations from WKY and SHRSP.

Topics: Acetylcholine; Animals; Antihypertensive Agents; Apamin; Blood Pressure; Body Weight; Charybdotoxin; Dose-Response Relationship, Drug; Enzyme Inhibitors; Female; Hypertension; In Vitro Techniques; Indomethacin; Male; Mesenteric Arteries; Nitric Oxide Synthase; Nitroarginine; Norepinephrine; Peptides, Cyclic; Potassium; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Time Factors; Vasoconstriction; Vasoconstrictor Agents; Vasodilator Agents

To elucidate pathophysiological roles of heme oxygenase (HO)-1 in regulation of vascular tone in vivo, we have developed and characterized transgenic (Tg) mice that overexpress HO-1 site specifically in vascular smooth muscle cells (VSMCs). The Tg mice were generated by use of human HO-1 cDNA under the control of SM22-alpha promoter. The HO-1 gene overexpression was demonstrated by Northern blot analysis and coincided with increases in the protein expression in VSMCs and total HO activities. Tg mice exhibited a significant increase in arterial pressure at various ages and displayed impaired nitrovasodilatory responses in isolated aortic segments versus nontransgenic littermates while enhancing their nitric oxide (NO) production. The pressure of Tg mice was unchanged by systemic administration of either N(omega)-nitro-L-arginine or SNP. Furthermore, the isolated aorta in these mice exhibited lesser extents of NO-elicited cGMP elevation via soluble guanylate cyclase (sGC), while exhibiting no notable downregulation of sGC expression. Such impairment of the NO-elicited cGMP increase was restored significantly by tin protoporphyrin IX, an HO inhibitor. On the other hand, 3-(5'-hydroxymethyl-2' furyl)-1-benzyl-indazol (YC-1), an NO-independent activator of sGC, increased cGMP and relaxed aortas from Tg mice to levels comparable with those from nontransgenic mice, which indicates that contents of functionally intact sGC are unlikely to differ between the two systems. These findings suggest that site-specific overexpression of HO-1 in VSMCs suppresses vasodilatory response to NO and thereby leads to an elevation of arterial pressure.

Topics: Animals; Aorta; Blood Pressure; Culture Techniques; Cyclic GMP; Enzyme Inhibitors; Guanylate Cyclase; Heme Oxygenase (Decyclizing); Heme Oxygenase-1; Hypertension; Kidney; Membrane Proteins; Metalloporphyrins; Mice; Mice, Transgenic; Muscle, Smooth, Vascular; Nitric Oxide; Nitric Oxide Synthase; Nitric Oxide Synthase Type II; Nitric Oxide Synthase Type III; Nitroarginine; Nitroprusside; Protoporphyrins; Vasodilation

Previous studies from our own laboratory have shown that abdominal aorta rings from two kidney - two clip hypertensive rats (HT) develop hypersensitivity to serotonin (SER) which is related to a decreased nitric oxide (NO) availability and enhanced thromboxane A2 production. In the present study we investigated whether calcium and prostanoid-NO interactions are involved in these findings. To this purpose, the aortic responses to SER were analyzed in calcium-free medium and in calcium-depleted aorta placed in normal medium. Moreover, effects of ridogrel (RID, an antagonist of TxA 2/PGH2 receptors and inhibitor of thromboxane synthetase) were analysed by cumulative dose-response curves to SER in the presence and in the absence of the NO synthase inhibitor N(omega)-nitro-L-arginine (NOLA). Vascular responses to SER in vessels from HT rats were associated with increased intracellular calcium mobilization. In addition, hypersensitivity to SER in HT group respect to sham group (SH) disappeared in the presence of RID, NOLA and RID plus NOLA. RID decreases the maximum tension to SER and this effect was prevented by NOLA. This inhibition was of a greater magnitude in rings from sham rats (SH): 34 +/- 6% than in HT rats: 15 +/- 6% (p < 0.05). Besides, RID decreased the sensibility to SER in the presence of NOLA only in the HT group. In conclusion, the present study suggests that SER hypersensitivity observed in HT rats is related to a facilitated intracellular calcium mobilization and enhanced TxA2-endoperoxide response. Changes in membrane SER-gated calcium channels opening are observed only during the early hypertensive period. Besides, the lower depressor effect of RID on the maximal tension to SER in aorta rings from HT rats are related with a decreased NO availability in this model of renovascular hypertension.

Topics: 6-Ketoprostaglandin F1 alpha; Animals; Aorta; Blood Pressure; Calcium; Dose-Response Relationship, Drug; Enzyme Inhibitors; Free Radical Scavengers; Hypertension; Kidney; Male; Muscle Contraction; Nitroarginine; Pentanoic Acids; Prostaglandin-Endoperoxide Synthases; Prostaglandins; Pyridines; Rats; Rats, Wistar; Serotonin; Thromboxane B2; Time Factors

The inhibitory role of NO on sympathetic-induced contraction of resistance vessels of spontaneously hypertensive rats (SHR) has not been defined. Accordingly, we investigated the effect of endothelial removal or NO synthase inhibition on vasoconstrictor responses to sympathetic stimulation or phenylephrine in perfused mesenteric beds isolated from normotensive rats (NR) and SHR. Electrical stimulation (10 to 64 Hz) of perivascular nerves elicited a frequency-dependent increase in perfusion pressure that was greater in preparations from SHR (maximal effect: 223.4+/-8.4 versus 117.6+/-10.3 mm Hg in NR, n=6, P<0.001), and endothelium removal did not affect these responses in arteries from NR but caused a significant shift to the left of the frequency-response curve in arteries from SHR. In arteries with endothelium, inhibition of NO synthase with N(G)-nitro-L-arginine (L-NNA, 50 micromol/L) augmented the vasoconstrictor responses to sympathetic stimulation in both NR and SHR preparations. In preparations that had the endothelium removed, however, L-NNA potentiated only the responses to sympathetic stimulation of NR arteries. Vasoconstrictor responses to phenylephrine was potentiated by endothelium removal and in the presence of L-NNA only when the endothelium was intact in both NR and SHR arteries. The number of NADPH-diaphorase-positive cells in the superior mesenteric sympathetic ganglion of SHR was significantly less compared with that of NR. In conclusion, these data suggest a prejunctional inhibitory action of non-endothelial-derived NO, most probably neuronal-derived NO, on sympathetic-mediated vasoconstriction in NR arteries. In contrast, enhancement of the sympathetic-mediated vasoconstriction in SHR arteries elicited by L-NNA can be attributed to inhibition of endothelial-derived NO.

Topics: Animals; Blood Pressure; Cyclooxygenase Inhibitors; Dose-Response Relationship, Drug; Electric Stimulation; Endothelium, Vascular; Enzyme Inhibitors; Female; Hypertension; In Vitro Techniques; Indomethacin; Mesenteric Arteries; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Phenylephrine; Rats; Rats, Inbred SHR; Rats, Wistar; Vasoconstriction; Vasoconstrictor Agents

Previously, we reported that aortic segments from rats made hypertensive with the nitric oxide synthase inhibitor N(omega)-nitro-L-arginine (L-NNA) exhibit enhanced contractile sensitivity to both alpha2-adrenergic receptor (alpha2-AR) stimulation and to KCl-induced depolarization. We hypothesized that increased contractile responses to these agents was due to a change in the common effector L-type voltage-dependent calcium channel (VDCC). In aortic segments from control and L-NNA-treated rats, contraction to the alpha2-AR agonist UK-14304 stimulated Ca2+ influx but released intracellular Ca2+ only in control arteries. UK-14304-induced contraction was blocked by the VDCC antagonist nifedipine in both control and L-NNA aortas but contraction of aortas from L-NNA-treated rats was blocked by lower concentrations. Calcium imaging studies in fura 2-loaded freshly isolated aortic vascular smooth muscle cells also demonstrated UK-14304-stimulated Ca2+ influx sensitive to nifedipine only in cells from L-NNA-treated rats. We conclude that alpha2-AR contraction in the rat aorta is mediated primarily by Ca2+ influx and that L-NNA-induced hypertension increases the dependence of this contraction on VDCCs.

Topics: 3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; Adrenergic alpha-Agonists; Animals; Aorta, Thoracic; Brimonidine Tartrate; Calcium; Calcium Channel Agonists; Calcium Channel Blockers; Calcium Channels, L-Type; Enzyme Inhibitors; Hypertension; Male; Muscle, Smooth, Vascular; Nifedipine; Nitric Oxide Synthase; Nitroarginine; Quinoxalines; Rats; Rats, Sprague-Dawley; Receptors, Adrenergic, alpha-2; Vasoconstriction

Chronic nitric oxide (NO) synthase inhibition in rats causes hypertension, renal vascular injury, and proteinuria. NO deficiency increases superoxide (O(2)(-)) activity, but the effects of antioxidant treatment on renal injury have not been studied in this model. Exposure of rats to N omega-nitro-L-arginine (L-NNA) for 4 d markedly decreased NO-dependent relaxation in aortic rings and increased glomerular and renal interstitial monocyte influx, but renal O(2)(-) activity was not increased. After 7 d, BP and proteinuria were significantly increased. After 21 d of L-NNA treatment, rats displayed severe hypertension, decreased GFR, marked proteinuria, glomerular ischemia, renal vascular and tubulointerstitial injury, and complete loss of NO-dependent relaxation. Renal O(2)(-) activity was markedly increased [lucigenin-enhanced chemiluminescence (LEC), 279 +/- 71 versus 50 +/- 7 counts/10 mg, P < 0.01; electron paramagnetic resonance spectroscopy, 0.57 +/- 0.05 versus 0.34 +/- 0.04 U/10 mg, P < 0.05]. Apocynin, a specific inhibitor of NADPH oxidase, and diphenyleneiodonium, an inhibitor of flavin-containing enzymes, completely inhibited LEC signals in vitro, whereas allopurinol had no effect, indicating that NAD(P)H oxidase plays a major role in superoxide production in the kidney. Endothelial function remained impaired during cotreatment with alpha-tocopherol and there was no effect on hypertension or tubulointerstitial injury, but glomerular ischemia, decreases in GFR, and renal vascular injury were prevented and proteinuria was ameliorated. Renal LEC signals were intermediate between control and L-NNA-alone values (181 +/- 84 counts/10 mg). Chronic NO synthase inhibition in rats results in marked increases in renal cortical O(2)(-) activity, mediated by flavin-dependent oxidases. The absence of early increases in renal O(2)(-) activity, in the presence of endothelial dysfunction and macrophage influx, indicates that increased renal O(2)(-) activity is neither attributable to NO deficiency per se nor solely related to macrophage influx. The improvement of glomerular function and amelioration of renal vasculitis and proteinuria with vitamin E cotreatment indicate that oxidants are involved in the pathogenesis of renal injury in this model. However, markedly impaired endothelial function and unabated hypertension persist with vitamin E treatment and seem to be directly attributable to NO deficiency.

Topics: Animals; Antioxidants; Aorta; Blood Pressure; Enzyme Inhibitors; Hypertension; Ischemia; Kidney; Kidney Cortex; Kidney Glomerulus; Macrophages; Male; Monocytes; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Proteinuria; Rats; Rats, Sprague-Dawley; Superoxides; Systole; Time Factors; Vasodilation; Vitamin E

The hypertensive rat model was made by chronic stress of electric foot-shocks and noises. On such hypertensive rats, when anesthetized with urethane and chloralose, the electroacupuncture (EA) to bilateral "Zusanli (st.36)" acupoints for 20 min, could result in a depressor (including both systolic and diastolic pressure) and bradycardiac response as well as an attenuation in the maximum of left ventricular pressure, end diastolic pressure and +/-dp/dt. In power spectrum analysis of heart rate variability aspect, EA could increase all total variance, very low frequency component, low frequency component and the ratio of low frequency component and high frequency component. When EA with microinjection of N(omega) - Nitro- L-Arginine , a blocker of the formation of nitric oxide, into the ventral periaqueductal gray matter (vPAG), the above effects of EA were abolished or reduced significantly. The results suggest that the depressor effect of EA on stress-induced hypertensive rats might be mediated by nitric oxide in the vPAG due to activation of sympathetic inhibitory system and by attenuated cardiac activities.

Topics: Acupuncture Points; Animals; Blood Pressure; Disease Models, Animal; Electroacupuncture; Heart Rate; Hypertension; Male; Nitric Oxide; Nitroarginine; Periaqueductal Gray; Rats; Rats, Wistar; Stress, Physiological

Nitric oxide attenuates both vasopressin-induced vasoconstriction and vasopressin release. We tested whether hypertension and renal dysfunction elicited by chronic inhibition of nitric oxide (NO) synthesis using N(G)-nitro-L-arginine (L-NNA) could be mediated in part by vasopressin V(1A) receptors. Male rats were treated orally for 6 weeks with L-NNA (15 mg/kg per day), a nonpeptide V(1A) receptor antagonist (2S)-1-[(2R,3S)-5-chloro-3-(2-chlorophenyl)-1-(3, 4-dimethoxybenzene-sulfonyl)-3-hydroxy-2, 3-dihydro-1H-indole-2-carbonyl]-pyrrolidine-2-carboxamide (SR 49059, 30 mg/kg per day), or a combination of SR 49059 and L-NNA (same doses), or they received no treatment. Both drugs were added to the food. Measurements were performed in conscious rats (urine collection in metabolic cages, tail-cuff arterial pressure) and at the end of the study in anesthetized rats (clearance measurements). L-NNA produced sustained hypertension, decreased glomerular filtration rate, and increased renal vascular resistance, plasma renin activity, and urinary albumin excretion. SR 49059 had no effect per se on these parameters and also did not attenuate the hypertension and renal dysfunction induced by L-NNA. Surprisingly, SR 49059 potentiated L-NNA-induced hypertension at the end of the 6-week treatment. However, the blood pressure response and the renal and mesenteric vasoconstriction elicited by exogenous vasopressin were attenuated in rats treated with SR 49059. L-NNA did not change plasma vasopressin concentration or 24-hour urinary vasopressin excretion. Our findings suggest that activation of vasopressin V(1A) receptors does not contribute to the hypertension and renal dysfunction induced by chronic NO synthesis inhibition. They also document unchanged plasma vasopressin concentration in NO-deficient hypertension.

Topics: Albuminuria; Animals; Antidiuretic Hormone Receptor Antagonists; Blood Pressure; Enzyme Inhibitors; Heart; Heart Rate; Hypertension; Indoles; Kidney; Male; Nitric Acid; Nitric Oxide Synthase; Nitroarginine; Organ Size; Pyrrolidines; Rats; Rats, Sprague-Dawley; Systole; Time Factors; Vasopressins

Involvement of endothelium-derived nitric oxide (EDNO) in alpha-adrenoceptor agonist-induced contractile responses was studied in isolated pulmonary arteries from Wistar Kyoto rats (WKY) and stroke-prone spontaneously hypertensive rats (SHRSP). In the presence of propranolol, noradrenaline-induced contraction was potentiated by endothelium removal or by N(G)-nitro-L-arginine (L-NOARG). The magnitude of the potentiation was independent of the noradrenaline concentration. L-NOARG also shifted the concentration-response curves for phenylephrine and methoxamine to the left and upward. Contractile responses to 2-amino-5,6,7,8, -tetrahydro-6-ethyl-4H-oxazolo-(5,4-d)-azepine-dihydrochloride (BHT-933) and 5-bromo-6-(2-imidazolin-2-ylamino)-quinoxaline (UK-14304) were augmented by L-NOARG in a concentration-dependent manner. There were no differences in the effects of L-NOARG on the contractile responses to alpha-adrenoceptor agonists between the preparations from WKY and SHRSP. Endothelium-dependent relaxation in response to acetylcholine was not impaired in the preparations from SHRSP when compared with those from WKY. These observations suggest that the contractile responses to the alpha(1)-adrenoceptor agonists were depressed mainly by basally released EDNO, while the responses to the alpha(2)-adrenoceptor agonists were depressed mainly by EDNO released in response to alpha(2)-adrenoceptor stimulation. The comparable influence of the endothelium on the alpha-adrenoceptor agonist-induced contractions in the pulmonary arteries from WKY and SHRSP, which were markedly different from other arteries, could be explained by the unaltered endothelium-dependent relaxation in the preparations from SHRSP.

Topics: Adrenergic alpha-Agonists; Animals; Blood Pressure; Body Weight; Dose-Response Relationship, Drug; Endothelium, Vascular; Hypertension; Methoxamine; Nitric Oxide; Nitroarginine; Norepinephrine; Phenylephrine; Pulmonary Artery; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Vasoconstriction

The purpose of this study was to examine the role played by a deficit in nitric oxide (NO) in contributing to the large cerebral infarcts seen in hypertension. Cerebral infarction was produced in rats by occlusion of the middle cerebral artery (MCA). Studies were performed in Sprague-Dawley (SD) rats subjected to NO synthase blockade (N(G)-nitro-L-arginine [L-NNA], 20 mg x kg(-1) x d(-1) in drinking water) and in spontaneously hypertensive stroke-prone rats (SHRSP). NO released in the brain in response to MCA occlusion was monitored with a porphyrinic microsensor in Wistar-Kyoto rats. The increment in NO released with MCA occlusion was 1.31+/-0.05 micromol/L in L-NNA-treated rats, 1.25+/-0.04 micromol/L in SHRSP, 2. 24+/-0.07 micromol/L in control SD rats, and 2.25+/-0.06 micromol/L in Wistar-Kyoto rats (P<0.0001 for control versus the other groups). Infarct sizes in the L-NNA-treated and control SD rats were 8.50+/-0. 8% and 5.22+/-0.7% of the brain weights, respectively (P<0.05). The basilar arterial wall was significantly thicker in L-NNA-treated rats compared with their controls. We conclude that both the deficit in NO and the greater wall thickness contribute to the larger infarct size resulting from MCA occlusion in SHRSP and in L-NNA-treated rats compared with their respective controls.

Topics: Animals; Cerebral Infarction; Enzyme Inhibitors; Hypertension; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Rats, Sprague-Dawley

1. The effects of graded inhibition of nitric oxide synthase (NOS) on blood pressure in the genetically hypertensive (GH) rat strain and NOS activity in regions of the brain (cerebellum, striatum, hippocampus, frontal cortex and medulla oblongata) as a measure of body NOS inhibition were studied. 2. Male GH and normotensive (N) rats (n = 7-10 per group) were given N(G)-nitro-L-arginine methyl ester (L-NAME; 2, 5, 10 or 20 mg/kg per day in drinking water) from age 7 weeks. Age- and weight-matched controls received water only. Systolic blood pressure (SBP) was measured weekly by the tail-cuff method from age 6 weeks. By age 10 weeks, rats were killed and NOS activity was measured. 3. Some GH rats that received over 5 mg/kg per day L-NAME developed stroke-like symptoms and were killed before the end of the treatment period. 4. No difference in NOS activity was found between untreated N and GH strains but, in those that received treatment, a graded inhibition was observed with increasing L-NAME dose levels. The frontal cortex in the GH strain given 20 mg/kg per day L-NAME had NOS inhibition of 90% where the N strain had 73% inhibition. Similar results were seen in the other areas of the brain. 5. Left ventricular mass, weight related, was significantly greater in the GH compared with N and was further elevated by treatment with L-NAME. 6. The SBP at 10 weeks was significantly elevated in GH rats by NOS inhibition with L-NAME in a dose-dependent manner; 25% for 2 mg/kg per day, 31% for 20 mg/kg per day (P < 0.001). There was a non-significant increase in BP in the N-treated groups (average change of 7.5%). 7. Nitric oxide synthase inhibition causing increased SBP in GH rats suggests an abnormality in the nitric oxide-L-arginine pathway in this strain.

Topics: Animals; Blood Pressure; Brain; Dose-Response Relationship, Drug; Enzyme Inhibitors; Hypertension; Hypertrophy, Left Ventricular; Male; Nitric Oxide Synthase; Nitroarginine; Rats; Rats, Wistar; Survival Rate

The present study was designed to determine whether and how potassium supplementation improves the endothelial function of carotid arteries of hypertensive Dahl rats. Dahl salt-sensitive rats were fed a high sodium diet, a high sodium plus potassium-supplemented diet, a normal rat chow, or a potassium-supplemented diet for 4 weeks. High sodium intake significantly increased the blood pressure, which was attenuated by potassium supplementation. The isometric tension of rat-isolated carotid rings was measured. In norepinephrine-precontracted rings, the relaxation in response to acetylcholine, adenosine 5'-diphosphate (ADP), and isoproterenol were significantly attenuated in hypertensive Dahl rats, which was improved by potassium supplementation. Pretreatment with N(G)-nitro-L-arginine methyl ester blocked the responses to acetylcholine and ADP, and eliminated the difference in relaxation in response to isoproterenol. The endothelium-independent relaxation in response to forskolin, S-nitroso-N-acetyl-DL-penicillamine, and sodium nitroprusside was significantly attenuated in hypertensive Dahl rats, which was not affected by potassium supplementation. The results indicated that salt-induced hypertension was associated with marked alterations in the endothelial and vascular smooth muscle functions of the carotid arteries of Dahl rats. Potassium supplementation ameliorated the endothelial but not the smooth muscle function. The protective effect of potassium appeared to be achieved through increased endothelial nitric oxide production. The current studies, in conjunction with our recent studies on nitric oxide synthase activity in the kidney, strongly suggest that potassium attenuates development of hypertension by increasing nitric oxide production in Dahl rats.

Topics: Acetylcholine; Adenosine Diphosphate; Adrenergic beta-Agonists; Animals; Carotid Arteries; Colforsin; Dietary Supplements; Enzyme Inhibitors; Hypertension; Isoproterenol; Male; Nitrates; Nitric Oxide; Nitrites; Nitroarginine; Nitroprusside; Penicillamine; Potassium, Dietary; Rats; Rats, Inbred Dahl; S-Nitroso-N-Acetylpenicillamine; Sodium Chloride; Sodium-Potassium-Exchanging ATPase; Vasodilation; Vasodilator Agents

The possible involvement of calcium and potassium channels in mediating the vascular actions of methyclothiazide (MCTZ), a thiazide diuretic, was investigated in isolated aortic rings from 12 week-old hypertensive rats. MCTZ (10(-4) M) inhibits the contractile response induced by addition of Ca2+ to a depolarizing solution, the maximal contracture is reduced by 87.16 +/- 6.4%. Furthermore this inhibitory effect was unaffected by charybdotoxine a selective blocker of calcium-activated K+ channels (Kca). This suggesting that MCTZ inhibits voltage-gated Ca2+ channels and blunts the Ca2+ entry into vascular smooth muscle cells. This inhibition was partially attenuated by either mechanical removal of the endothelium or N omega-nitro-L-arginine (NOLA) treatment, suggesting that MCTZ effects are also mediated by an endothelium-dependent mechanism involving endothelium-dependent relaxing factor (EDRF)/nitric oxide (NO) release. Taken together, these observations could point to a role of voltage-gated Ca2+ channels and endothelial release of EDRF/NO in the antihypertensive action of MCTZ.

Topics: Animals; Aorta; Calcium; Calcium Channel Blockers; Calcium Channels; Charybdotoxin; Diuretics; Endothelium, Vascular; Enzyme Inhibitors; Hypertension; Ion Channel Gating; Male; Methyclothiazide; Muscle, Smooth, Vascular; Nitric Oxide; Nitroarginine; Potassium Channel Blockers; Potassium Channels; Rats; Rats, Inbred SHR; Sodium Chloride Symporter Inhibitors; Vasoconstriction; Vasodilator Agents

Angiotensin-converting enzyme (ACE) inhibitor improves the impaired hyperpolarization and relaxation to acetylcholine (ACh) via endothelium-derived hyperpolarizing factor (EDHF) in arteries of spontaneously hypertensive rats (SHR). We tested whether the angiotensin type 1 (AT(1)) receptor antagonist also improves EDHF-mediated responses and whether the combined AT(1) receptor blockade and ACE inhibition exert any additional effects. SHR were treated with either AT(1) receptor antagonist TCV-116 (5 mg. kg(-1). d(-1)) (SHR-T), enalapril (40 mg. kg(-1). d(-1)) (SHR-E), or their combination (SHR-T&E) from 8 to 11 months of age. Age-matched, untreated SHR (SHR-C) and Wistar Kyoto (WKY) rats served as controls (n=8 to 12 in each group). Three treatments lowered blood pressure comparably. EDHF-mediated hyperpolarization to ACh in mesenteric arteries in the absence or presence of norepinephrine was significantly improved in all treated SHR. In addition, the hyperpolarization in the presence of norepinephrine was significantly greater in SHR-T&E than in SHR-E (ACh 10(-5) mol/L with norepinephrine: SHR-C -7; SHR-T -19; SHR-E -15; SHR-T&E -22; WKY -14 mV). EDHF-mediated relaxation, assessed in the presence of indomethacin and N:(G)-nitro-L-arginine, was markedly improved in all treated SHR. Hyperpolarization and relaxation to levcromakalim, a direct opener of ATP-sensitive K(+)-channel, were similar in all groups. These findings suggest that AT(1) receptor antagonists are as effective as ACE inhibitors in improving EDHF-mediated responses in SHR. The beneficial effects of the combined AT(1) receptor blockade and ACE inhibition appears to be for the most part similar to those of each intervention.

Topics: Acetylcholine; Administration, Oral; Angiotensin Receptor Antagonists; Animals; Anti-Inflammatory Agents, Non-Steroidal; Antihypertensive Agents; Benzimidazoles; Biological Factors; Biphenyl Compounds; Cromakalim; Disease Models, Animal; Drug Therapy, Combination; Enalapril; Endothelium, Vascular; Enzyme Inhibitors; Hypertension; In Vitro Techniques; Indomethacin; Male; Nitroarginine; Norepinephrine; Potassium Channels; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Receptor, Angiotensin, Type 1; Receptor, Angiotensin, Type 2; Renin-Angiotensin System; Tetrazoles

1. L-arginine prevents adrenocorticotrophin (ACTH)-induced hypertension in the rat. To confirm that this effect is mediated through the nitric oxide (NO) system, we examined whether N-nitro-L-arginine (NOLA) could reverse the L-arginine-induced blockade of ACTH-induced hypertension. 2. Blood pressure and metabolic parameters were examined in sham-, ACTH-, L-arginine + sham-, NOLA + sham-, ACTH + L-arginine- and ACTH + L-arginine + NOLA-treated Sprague-Dawley rats (n = 40). 3. Adrenocorticotrophin treatment increased systolic blood pressure (SBP), water intake and urine output and decreased bodyweight. N-Nitro-L-arginine alone increased SBP without affecting metabolic variables. L-Arginine alone did not affect blood pressure. The SBP was lower in L-arginine + ACTH- than ACTH-treated rats (P < 0.001), but was higher following ACTH + L-arginine + NOLA than ACTH + L-arginine (P < 0.05). 4. N-Nitro-L-arginine reversed the blood pressure-lowering effect of L-arginine in ACTH-induced hypertension in the rat, supporting the notion that NO plays a role in the hypertension.

Topics: Adrenocorticotropic Hormone; Animals; Arginine; Blood Pressure; Drinking; Eating; Enzyme Inhibitors; Hypertension; Male; Nitric Oxide; Nitric Oxide Synthase; Nitric Oxide Synthase Type III; Nitroarginine; Rats; Rats, Sprague-Dawley

To compare coronary dilation in uninephrectomized hypertensive deoxycorticosterone acetate (DOCA)-salt rats (HTRs), treated for 2 or 4 weeks, with age-matched uninephrectomized normotensive rats (NTRs). DESIGN AND METHODS Coronary perfusion pressure was recorded in isolated hearts perfused at a constant flow rate to evaluate coronary resistance.. A decreased vasoconstriction due to NG-nitro-Larginine (NNLA, 30 pmol/I) in hearts from HTRs suggested a reduced basal nitric oxide (NO) release. In contrast, coronary vasodilation due to the NO donor, sodium nitroprusside (3 pmol/I), remained unaffected in 2-week HTRs, and was enhanced in 4-week HTRs. Cumulative dose-response curves to bradykinin induced an important vasodilation in NTRs, with a maximal response that remained unaffected in the presence of either NNLA (30 pmol/I), indomethacin (10 pmol/l) or the two combined. In contrast, hearts from HTRs showed a diminished maximal relaxation to bradykinin, suggesting an altered endothelium-dependent relaxation. The presence of NNLA or indomethacin had no effect on the weak relaxation observed in HTRs. However, NNLA and indomethacin combined unmasked an important relaxation due to bradykinin in HTRs. The addition of clotrimazole (1 pmol/I) to NNLA and indomethacin blunted the relaxation due to bradykinin in both NTRs and HTRs. Perfusion with superoxide dismutase (120 IU/ml) restored most of the coronary relaxation due to bradykinin in hearts from HTRs. Bradykinin-induced prostaglandin 12 (PGI2) and E2 (PGE2) production was unaffected by hypertension. No increase in thromboxane A2 (TXA2) due to bradykinin was detected. Finally, reduced reactivity to papaverine and forskolin was observed in hearts from HTRs.. DOCA-salt hypertension is associated with alterations in coronary reactivity. Basal NO formation appears to be reduced in HTRs, but the intact relaxation to exogenous NO suggests a preserved guanylate cyclase pathway. In addition, alteration in adenylate cyclase activity, and not in prostaglandin production, may explain the blunted cAMP-mediated responses in HTRs. The combined nitric-oxide synthase (NOS) and cyclo-oxygenase (COX) inhibition unmasked an endothelium-derived hyperpolarizing factor (EDHF) involvement in the coronary dilation due to bradykinin in hearts from HTRs, suggesting that endothelial NO and PGI2, although unable to induce coronary smooth-muscle relaxation, can inhibit EDHF production in HTRs. Impairment in the adenylate cyclase pathway and the suppression of NO by free radicals may explain the blunted vasodilation in DOCA-salt hypertension.

Topics: Animals; Bradykinin; Coronary Circulation; Coronary Vessels; Desoxycorticosterone; Eicosanoids; Endothelium, Vascular; Guanylate Cyclase; Heart; Hypertension; In Vitro Techniques; Male; Nitric Oxide; Nitroarginine; Papaverine; Perfusion; Rats; Rats, Sprague-Dawley; Sodium Chloride; Vasodilation

Corticotrophin (ACTH)-induced hypertension in the rat is prevented by L- but not D-arginine. We examined the effects of exogenous corticosterone in the male Sprague Dawley (SD) rat to determine whether ACTH-induced hypertension is mediated by corticosterone.. Exogenous corticosterone (10, 20 or 40 mg/kg per day) or sham (polyethylene glycol (PEG) 1 ml/kg per day) was injected subcutaneously in divided doses (s/c b.d.) over 15 treatment days to 40 SD rats (n = 10 each group). Subsequently, the effects of L-arginine, D-arginine or L-arginine + N-nitro-L-arginine (NOLA) on corticosterone-induced hypertension (corticosterone 20 mg/kg per day) were examined. Systolic blood pressure (SBP) and metabolic parameters were measured every two days.. Twenty and 40 mg/kg per day of corticosterone increased SBP compared with sham (P< 0.01, P< 0.05 respectively, sham versus respective group). Forty mg/kg per day of corticosterone raised serum corticosterone concentration compared with sham (502 +/- 20 versus 364 +/- 25 ng/ml, P < 0.001). L-arginine prevented the rise in SBP produced by corticosterone (131 +/- 3 to 131 +/- 2 mmHg, control versus day 10) but D-arginine did not (129 +/- 3 to 142 +/- 4 mmHg on day 8, P < 0.01). NOLA blocked the effect of L-arginine and amplified the rise in blood pressure produced by corticosterone (130 +/- 3 to 171 +/- 6 mmHg on day 10, P < 0.001).. The haemodynamic features of ACTH-induced hypertension were reproduced by corticosterone excess, at concentrations of corticosterone similar to those in studies of exogenous ACTH administration. It is likely that ACTH-stimulated adrenal production of corticosterone accounts for the features of ACTH-induced hypertension in the rat

Topics: Adrenocorticotropic Hormone; Animals; Arginine; Blood Pressure; Body Weight; Corticosterone; Drinking; Eating; Hypertension; Male; Nitrates; Nitrites; Nitroarginine; Rats; Rats, Sprague-Dawley; Stereoisomerism; Urination

This study was designed to determine the influence of neuronal nitric oxide synthase (nNOS) in tubular flow-dependent regulation of afferent arteriolar diameter in hypertensive Sprague-Dawley rats that received 60 ng/min angiotensin II (Ang II) subcutaneously for 13 days. Systolic blood pressure of control and Ang II-infused rats averaged 122+/-2 (n=23) and 194+/-2 mm Hg (n=24). Afferent arteriolar responses to the nNOS inhibitor S-methyl-L-thiocitrulline (L-SMTC; 0.1 to 10 micromol/L) and the nonselective NOS inhibitor Nomega-nitro-L-arginine (L-NNA; 1 to 100 micromol/L) were assessed in vitro using the blood-perfused juxtamedullary nephron preparation. At a perfusion pressure of 160 mm Hg, afferent arteriolar diameters from control and Ang II-infused rats averaged 18.7+/-1.1 microm (n=8) and 18.1+/-1.1 microm (n=9), respectively, and decreased by 19. 9+/-1.5% and 11.8+/-1.1%, respectively, in response to 10 micromol/L L-SMTC. The L-SMTC-induced afferent arteriolar constriction was significantly greater in control than in Ang II-infused rats. In contrast, 100 micromol/L L-NNA constricted afferent arterioles similarly in both control (n=8) and Ang II-infused (n=7) rats. After transection of the loops of Henle to interrupt flow to the macula densa, the vasoconstrictor responses to L-SMTC but not to L-NNA were reversed. Increasing distal volume delivery by addition of 10 mmol/L acetazolamide to the blood perfusate significantly enhanced the afferent arteriolar constrictor responses to 10 micromol/L L-SMTC (34.5+/-4.8%, n=7) in normotensive rats. In contrast, in Ang II-infused rats, acetazolamide treatment did not enhance the responses to L-SMTC (n=8). These results indicate that chronic Ang II infusion reduces the ability of nNOS-derived nitric oxide to counteract the afferent arteriolar response to increased distal tubular flow.

Topics: Acetazolamide; Angiotensin II; Animals; Arterioles; Blood Pressure; Citrulline; Enzyme Inhibitors; Hypertension; Juxtaglomerular Apparatus; Kidney Medulla; Male; Microscopy, Video; Muscle, Smooth, Vascular; Nephrons; Nitric Oxide Synthase; Nitric Oxide Synthase Type I; Nitroarginine; Rats; Rats, Sprague-Dawley; Thiourea; Vasoconstriction; Vasodilation

Behavioral stress and aging are associated with an increase in vascular disease. This study determined the mechanisms contributing to changes in endothelium-dependent relaxation of isolated coronary arteries (300-350 micrometers) induced by exposure to 10 days of air-jet stress (2 h/day) in young (3 mo) and old (18 mo) male borderline hypertensive rats (BHR). Aging, alone, did not alter endothelium-dependent relaxation to acetylcholine (ACh) quantitatively but did alter the mechanisms contributing to relaxation to ACh, which was largely dependent on nitric oxide synthase (NOS) in vessels from old, but not young, BHR. Behavioral stress resulted in an enhanced relaxation to ACh that was dependent on NOS in vessels from young stressed compared with young control BHR. Conversely, relaxation to ACh was reduced in coronary arteries from old stressed compared with old control BHR. In vessels from old control BHR, there was an NOS-independent component of relaxation mediated by opening of K+ channels that was absent in vessels from old stressed BHR. The superoxide anion scavenger, tiron, partially restored relaxation, and inhibition of cyclooxygenase largely restored relaxation to ACh in vessels from old stressed BHR. In summary, the effect of behavioral stress was age dependent. ACh-induced relaxation of coronary arteries was enhanced in an NOS-dependent manner in young BHR and was impaired in old BHR due to superoxide anions, vasoconstrictor cyclooxygenase products, and a loss of K+ channel-mediated relaxation.

Topics: Acetylcholine; Aging; Animals; Arteries; Coronary Vessels; Enzyme Inhibitors; Female; Hypertension; Male; Nitroarginine; Physical Stimulation; Rats; Rats, Inbred SHR; Rats, Inbred Strains; Rats, Inbred WKY; Stress, Psychological; Vasodilation; Vasodilator Agents

Excess NaCl increases blood pressure in some strains of animals but not others. An 8% NaCl diet did not change renal thiazide receptor (TZR) density in two salt-resistant normotensive rat strains (Wistar-Kyoto and Sprague-Dawley) [Fanestil, D. D., D. A. Vaughn, and P. Blakely. Am. J. Physiol. 273 (Regulatory Integrative Comp. Physiol. 42): R1241-R1245, 1997]. However, the renal response to salt differs in normal and hypertensive kidneys [Rettig, R., N. Bandelow, O. Patschan, B. Kuttler, B. Frey, and A. Uber. J. Hum. Hypertens. 10: 641-644, 1996]. Therefore, we examined two strains with salt-aggravated hypertension. Renal TZR did not change when Dahl-S (salt sensitive) animals became hypertensive with 8% dietary NaCl. In contrast, renal TZR decreased 34%, whereas blood pressure increased further, in SHR with 8% dietary NaCl. Blood pressure increased after NG-nitro-L-arginine in SHR, but renal TZR did not change, indicating the salt-induced decrease in TZR in SHR cannot be attributed nonspecifically to elevated arterial pressure. We conclude that the renal response to NaCl-induced increases in blood pressure can be genetically modulated independently of the genes that mediate either the primary hypertension or the salt sensitivity of the hypertension. This finding may be of use in future studies directed at identifying genotypes associated with salt-dependent hypertension.

Topics: Animals; Carrier Proteins; Diet; Drug Resistance; Enzyme Inhibitors; Hypertension; Kidney; Male; Nitric Oxide Synthase; Nitroarginine; Rats; Rats, Inbred Dahl; Rats, Inbred SHR; Receptors, Drug; Sodium Chloride; Sodium Chloride Symporters; Solute Carrier Family 12, Member 3; Symporters

Differences in the acetylcholine (ACh)-induced endothelium-dependent relaxation and hyperpolarization of the mesenteric arteries of Wistar Kyoto rats (WKY) and stroke-prone spontaneously hypertensive rats (SHRSP) were studied. Relaxation was impaired in preparations from SHRSP and tendency to reverse the relaxation was observed at high concentrations of ACh in these preparations. Relaxation was partly blocked by NG-nitro-L-arginine (L-NOARG, 100 microM) and, in the presence of L-NOARG, tendency to reverse the relaxation was observed in response to higher concentrations of ACh, even in preparations from WKY. The relaxation remaining in the presence of L-NOARG was also smaller in preparations from SHRSP. The tendency to reverse the relaxation observed at higher concentrations of ACh in preparations from SHRSP or WKY in the presence of L-NOARG were abolished by indomethacin (10 microM). Elevating the K+ concentration of the incubation medium decreased relaxation in the presence of both indomethacin and L-NOARG. Relaxation in the presence of L-NOARG and indomethacin was reduced by the application of both apamin (5 microM) and charybdotoxin (0.1 microM). This suggests that the relaxation induced by ACh is brought about by both endothelium-derived relaxing factor (EDRF, nitric oxide (NO)) and hyperpolarizing factor (EDHF), which activates Ca2+-sensitive K+ channels. Electrophysiological measurement revealed that ACh induced endothelium-dependent hyperpolarization of the smooth muscle of both preparations in the presence of L-NOARG and indomethacin; the hyperpolarization being smaller in the preparation from SHRSP than that from WKY. These results suggest that the release of both NO and EDHF is reduced in preparations from SHRSP. In addition, indomethacin-sensitive endothelium-derived contracting factor (EDCF) is released from both preparations; the release being increased in preparations from SHRSP.

Topics: Acetylcholine; Animals; Apamin; Blood Pressure; Body Weight; Bridged Bicyclo Compounds, Heterocyclic; Charybdotoxin; Dose-Response Relationship, Drug; Endothelium, Vascular; Enzyme Inhibitors; Fatty Acids, Unsaturated; Glyburide; Hydrazines; Hypertension; In Vitro Techniques; Indomethacin; Membrane Potentials; Mesenteric Arteries; Methylene Blue; Muscle Relaxation; Muscle, Smooth, Vascular; Nitric Oxide; Nitroarginine; Nitroprusside; Potassium; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Systole; Tetraethylammonium; Vasodilation; Vasodilator Agents

In pregnant rats during hypertension induced by NO synthase inhibition, endothelin (ET) plasma levels are increased as in some preeclamptic women. Previously, the enhanced vasodepressor effect of endothelin-1 (ET-1) has been observed in this model, thus we decided to study the relaxation induced by ET-1 on the aorta. Non-pregnant or pregnant Wistar rats (n = 7 by group) were fed for 7 days (day 13-day 20) on a nitroarginine-enriched diet (L-NNA, 0.063% i.e. 30 mg/kg/day) or a control diet. Systolic blood pressure, measured by the tail cuff method on conscious rats at day 20 of gestation, was raised by the chronic L-NNA treatment (mean +/- s.e.m., mmHg, p < 0.001: pregnant L-NNA treated, 145 +/- 1.84 vs. pregnant control, 101 +/- 2.00 and non-pregnant L-NNA treated, 148 +/- 3.11 vs. non-pregnant control, 119 +/- 1.80). On day 20 ex vivo aortic ring relaxation was produced by ET-1 in vessels previously precontracted with norepinephrine only when endothelium was present. In control rats, ET-1 (10(-8) to 5 x 10(-8) M) produced a short but significant relaxation (mean value between 4 to 19%) followed by a long-lasting contracting phase, and a higher ET-1 concentration (10(-7) M) only produced contraction. Chronic L-NNA treatment decreased the level of relaxation (at least p < 0.05, in non-pregnant and pregnant rats) and with a 30 min L-NAME (10(-4) M) preincubation, relaxation was completely inhibited in non-pregnant and pregnant rats. BQ-123, an ETA receptor antagonist, did not produce any effect on ET-1 induced relaxation. BQ-788, an ETB receptor antagonist, significantly decreased it. In conclusion, in female rats, as in male rats, ET-1 induces a transient relaxation in the preconstricted aorta which involves endothelial ETB receptors. Despite a decrease in the systemic vascular reactivity during late gestation, the vasodilating and vasoconstricting properties of ET-1 on the aorta are not changed.

Topics: Animals; Antihypertensive Agents; Aorta, Thoracic; Endothelin Receptor Antagonists; Endothelin-1; Enzyme Inhibitors; Female; Growth; Hypertension; Male; Muscle Relaxation; Muscle, Smooth, Vascular; Nitric Oxide Synthase; Nitric Oxide Synthase Type III; Nitroarginine; Norepinephrine; Oligopeptides; Peptides, Cyclic; Piperidines; Pregnancy; Rats; Rats, Wistar; Vasoconstrictor Agents

The effect of daily spontaneous running (DSR) on endothelial function was examined in spontaneously hypertensive rats (SHR). Following 8-11 weeks of DSR (n=15) or sedentary control (SED, n=15), rats were instrumented with arterial and venous catheters and mesenteric and iliac Doppler ultrasonic flow probes. Hemodynamic responses to vasodilator-mediated substances were determined under two experimental conditions; 1) bolus injection of indomethacin (10 mg/kg) and 4 bolus doses of acetylcholine (0.5-2.0 microg/kg); 2) bolus injection of N(omega)-nitro-L-arginine (5 mg/kg) and 4 bolus doses of nitroglycerin (3-12 microg/kg). Hindlimb vascular conductance decreased more in response to indomethacin in DSR vs. SED rats (-18.3+/-2.8% vs. -10.4+/-2.5%). However, the mesenteric or hindlimb vascular conductance responses to N(omega)-nitro-L-arginine were not different between DSR and SED rats. DSR also enhanced mesenteric and hindlimb vascular conductance responses to acetylcholine. Results suggest that DSR enhances acetylcholine-induced vasodilation in SHR.

Topics: Acetylcholine; Animals; Cyclooxygenase Inhibitors; Endothelium, Vascular; Female; Follow-Up Studies; Ganglionic Blockers; Hexamethonium; Hindlimb; Hypertension; Iliac Artery; Indomethacin; Male; Mesenteric Arteries; Muscle, Smooth, Vascular; Nitroarginine; Nitroglycerin; Physical Conditioning, Animal; Rats; Rats, Inbred SHR; Ultrasonography, Doppler; Vasodilation; Vasodilator Agents

To investigate the effects of chronic treatment with simvastatin (SV) on endothelium-dependent relaxation and ouabain-induced contractions in aortic rings from spontaneously hypertensive rats (SHR), comparing with normotensive Wistar-Kyoto rats (WKY).. After a 12-week period of administration of 1 or 2 mg/kg SV to SHR and WKY, systolic blood pressure (SBP) and vascular reactivity in endothelium-intact aortic rings were assessed.. Relaxation in response to acetylcholine (ACh) in WKY remained unaltered, but in SHR treated with 1 mg/kg SV, enhanced ACh-induced relaxation (P<0.05 versus untreated SHR) reached values observed in untreated WKY. The 2 mg/kg treatment also improved ACh relaxation (P<0.01 and P<0.05 versus untreated SHR and WKY respectively). Inhibiting cyclo-oxygenase (COX) with indomethacin (INDO) improved ACh relaxation in SHR (P<0.05) but not in WKY, independent of treatment with SV. Inhibition of nitric oxide synthase (NOS) with N(G)-nitro-L-arginine (L-NOARG) abolished ACh relaxations in all cases (P<0.001). The result was unaltered when combining INDO plus L-NOARG. SV treatment also decreased ouabain-induced contractions in endothelium-intact aortic rings from SHR, diminishing the percentage effect of contraction from 64.56+/-2.95 (untreated SHR) to 26.98+/-7.06 and 38.10+/-8.21 (1 and 2 mg/kg treated SHR respectively). Response to ouabain in WKY was not significantly affected by SV treatment. Chronic treatment of SHR with SV improves endothelium-dependent ACh relaxation of the aortic rings, probably by an NO-involving mechanism more than by inhibiting contractile COX-derived factors. An improvement in endothelial modulation of ouabain-induced contractions was also observed after treatment with SV in SHR, which might be due to an inhibition of a calcium-sodium exchanger.

Topics: Acetylcholine; Animals; Aorta, Thoracic; Blood Pressure; Cardiotonic Agents; Endothelium, Vascular; Enzyme Inhibitors; Follow-Up Studies; Hydroxymethylglutaryl-CoA Reductase Inhibitors; Hypertension; Male; Nitric Oxide Synthase; Nitroarginine; Ouabain; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Simvastatin; Vasodilation; Vasodilator Agents

Protease-activated receptor-2 (PAR-2) can be activated after proteolysis of the amino terminal of the receptor by trypsin or by synthetic peptides with a sequence corresponding to the endogenous tethered ligand exposed by trypsin (eg, SLIGRL-NH(2)). PAR-2 mediates nitric oxide (NO)-dependent dilatation in cerebral arteries, but it is unknown whether PAR-2 function is altered in cardiovascular diseases. Since hypertension selectively impairs NO-mediated cerebral vasodilatation in response to acetylcholine and bradykinin, we sought to determine whether PAR-2-mediated vasodilatation is similarly adversely affected by this disease state.. We studied basilar artery responses in Wistar-Kyoto rats (WKY) (normotensive) and spontaneously hypertensive rats (SHR) in vivo (cranial window preparation) and in vitro (isolated arterial rings). The vasodilator effects of acetylcholine, sodium nitroprusside, and activators of PAR-2 and protease-activated receptor-1 (PAR-1) were compared in WKY versus SHR. Immunohistochemical localization of PAR-2 was also assessed in the basilar artery.. Increases in basilar artery diameter in response to acetylcholine were 65% to 85% smaller in SHR versus WKY, whereas responses to sodium nitroprusside were not different. In contrast to acetylcholine, vasodilatation in vivo to SLIGRL-NH(2) was largely preserved in SHR, and SLIGRL-NH(2) was approximately 3-fold more potent in causing vasorelaxation in SHR versus WKY in vitro. In both strains, responses to SLIGRL-NH(2) were abolished by N(G)-nitro-L-arginine, an inhibitor of NO synthesis. Activators of PAR-1 had little or no effect on the rat basilar artery. PAR-2-like immunoreactivity was observed in both the endothelial and smooth muscle cells of the basilar artery in both strains of rat.. These data indicate that NO-mediated vasodilatation to PAR-2 activation is selectively preserved or augmented in SHR and may suggest protective roles for PAR-2 in the cerebral circulation during chronic hypertension.

Topics: Acetylcholine; Animals; Cerebral Arteries; Chronic Disease; Enzyme Inhibitors; Hypertension; Male; Nitroarginine; Nitroprusside; Oligopeptides; Peptide Fragments; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Receptor, PAR-1; Receptor, PAR-2; Receptors, Thrombin; Vasodilation

When the potent inhibitor of nitric oxide (NO) synthesis NG-nitro-L-arginine (L-NNA) was incorporated into the diet, hypertension was induced and sustained due to the effects of the long-term inhibition of endothelium-dependent relaxing factor (EDRF)/NO. The effects of L-NNA on normotensive rats of four strains (Donryu, Sprague-Dawley (SD), Wistar, and Wistar-Kyoto (WKY)) were compared relative to control rats. L-NNA administration caused a sharp initial increase in systolic blood pressure (SBP) at 2 weeks in all animals, and this was followed by a gradual and steady increase until 4 weeks. At the end of the experiments (5 weeks), the mean SBP of Donryu and SD rats was decreased. The maximum blood pressure of Donryu and Wistar rats during the experiments exceeded 200 mmHg, but that of SD and WKY rats was below 200 mmHg. Body weight loss and death were observed only in L-NNA-fed Donryu rats. Pathological changes in the kidneys and the morbidity rates for the lesions were determined, and indicated that the Donryu L-NNA group was 100% positive. These results suggest that the Donryu strain is more sensitive to L-NNA than the other strains. That dietary L-NNA-induced hypertension in normotensive rats of the four strains provides a new artificially-induced hypertensive model in which vasoconstriction occurs mainly due to EDRF deficiency.

Topics: Animals; Blood Pressure; Body Weight; Diet; Enzyme Inhibitors; Hypertension; Kidney; Male; Nephrosclerosis; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Organ Size; Potassium; Rats; Rats, Inbred WKY; Rats, Sprague-Dawley; Rats, Wistar; Sodium; Species Specificity

Previous studies provided evidence for an interaction between the brain nitrergic and vasopressinergic systems in normotensive and spontaneously hypertensive rats in regulation of the cardiovascular functions. The present study was designed to determine the role of the brain nitric oxide (NO) in regulation of basal blood pressure and its interaction with vasopressin (AVP) in rats with renin dependent transgenic hypertension TGRmRen2(27) (TGR). The experiments were performed on conscious hypertensive TGR and normotensive Sprague-Dawley (SD) rats. Both groups were chronically instrumented with the left cerebral ventricle cannula (LCV) and femoral arterial catheter. LCV application of 2.3 nmol (0.5 microg) of N(G)-nitro-L-arginine (L-NNA) an inhibitor of NO synthesis significantly elevated blood pressure (MAP) in TGR but not in SD rats. In contrast administration of NO donor S-acetyl-N-penicillamine (SNAP) produced significant decrease of MAP only in SD rats. LCV application of AVP (10 ng) elicited comparable increases of MAP in TGR and SD rats. Pretreatment with L-NNA significantly potentiated pressor response to AVP in TGR rats but not in SD rats. The results provide evidence that increased production of intrabrain NO may play a significant blood pressure buffering role in TGR rats both under baseline conditions and during activation of the vasopressinergic system.

Topics: Animals; Animals, Genetically Modified; Arginine Vasopressin; Blood Pressure; Brain; Heart Rate; Hypertension; Nitric Oxide; Nitric Oxide Donors; Nitroarginine; Penicillamine; Rats; Rats, Sprague-Dawley; Renin; S-Nitroso-N-Acetylpenicillamine; Time Factors

We have previously shown that conduit arteries of normotensive (WKY) and hypertensive (SHR) Japanese rats differ from normotensive (LN) and hypertensive (LH) Lyon rats in terms of lower aortic thickness and higher collagen III content, whereas differences in vasoactive properties are unknown.. Aortic rings with (E+) and without (E-) endothelium were studied under resting and noradrenaline-stimulated conditions in the presence of N(omega)-nitro-L-arginine (L-NNA) alone or in association with indomethacin, bosentan and/or BQ123.. Under resting conditions, aortas of normotensive and hypertensive Japanese rats differed from Lyon rats by higher developed tension in the presence of L-NNA and endothelium. In the absence of endothelium, normotensives differed from hypertensives in terms of stronger developed tensions in the presence of L-NNA in the two strains. Addition of indomethacin to L-NNA induced relaxation in E+ SHR and E- WKY and contraction in E-LH. By contrast, tensions were unchanged after addition of bosentan and BQ123. Under stimulated conditions, tensions were equally increased by L-NNA in E+ and unchanged in E- both in Japanese and Lyon rats whether they were normotensive or hypertensive, and indomethacin (but not bosentan) elicited higher response in Lyon than in Japanese rats in E+ and E- aorta.. Under NO synthase inhibition, the vasoactive properties of Japanese and Lyon aorta differ in the presence of a cyclo-oxygenase blocker but not endothelin blockers. These results indicate that the aorta vasorelaxant tone is associated to prostanoid regulation in Lyon but not in Japanese rats. This observation appears dependent on the genetic and/or environmental background linked to the origin and not the presence of hypertension.

Topics: Animals; Aorta; Endothelium, Vascular; Enzyme Inhibitors; Hypertension; Nitroarginine; Norepinephrine; Rats; Rats, Inbred SHR; Rats, Inbred Strains; Rats, Inbred WKY; Species Specificity; Vasoconstriction; Vasoconstrictor Agents

1. Thoracic aortas of normotensive (Wistar-Kyoto (WKY) and Lyon normotensive (LN)) and hypertensive (spontaneously hypertensive rats (SHR) and Lyon hypertensive (LH)) rats from two groups (Japanese (WKY rats and SHR) and Lyon (LN and LH rats)) were compared using organ chambers. Changes in endothelium and smooth muscle reactivity to noradrenaline (NA), carbamylcholine and N omega-nitro-L-arginine (L-NNA) were analysed to distinguish between changes in reactivity that are associated with the presence of hypertension and those that are dependent on group (Japanese vs Lyon). 2. Aortas of hypertensive rats had lower pD2 values for NA than aortas from normotensive rats. These differences were associated with hypertension (P < 0.005 and P < 0.01) and group (P < 0.005 and P < 0.005) in presence or absence of endothelium, respectively, whereas no difference was seen in the maximal developed tension in response to NA. 3. Aortas also differed by a reduced ability to relax in response to carbamylcholine in hypertensive rats; this effect is hypertension (P < 0.05) and group (P < 0.005) dependent, without any change in carbamylcholine pD2 values. 4. Changes in maximum developed tension in the presence of L-NNA were found to be endothelium dependent and pressure and group independent. Furthermore, the change in tension induced by L-NNA appears significantly more pronounced in SHR than in LH rats (P < 0.05). 5. These results indicate that the common defect associated with hypertension appears to be linked to the endothelium through alpha-adrenoceptors and muscarinic receptors in both the Japanese and Lyon groups. However, SHR differs markedly from LH rats by having a higher developed tension in response to NA, this increased tension being counterbalanced by the release of nitric oxide, as observed in the presence of L-NNA.

Topics: Animals; Aorta, Thoracic; Carbachol; Dose-Response Relationship, Drug; Endothelium, Vascular; Hypertension; Male; Muscle Contraction; Muscle, Smooth, Vascular; Nitroarginine; Norepinephrine; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Species Specificity

We hypothesized that during hypertension, the impairment of mediation of shear stress-induced dilation by nitric oxide (NO) is due to the prevailing hemodynamic forces, and that mediation of this response by NO should still be present in young spontaneously hypertensive rats (SHR). Thus, responses to increases in perfusate flow eliciting increases in wall shear stress were investigated in pressurized (80 mm Hg), isolated arterioles ( approximately 70 to 100 microm) of the left or right gracilis muscle obtained from the same WKY and SHR at 4 and 12 weeks of age. Flow-induced dilations were similar in WKY and SHR at 4 weeks (maximum, 26.5+/-1.8 and 24. 2+/-2.0 microm, respectively). Also, the middle of the upward portion of the shear stress-diameter curves was similar in arterioles of the 2 strains. Inhibition of NO synthase with N(omega)-nitro-L-arginine (L-NNA) or inhibition of synthesis of prostaglandins (PGs) with indomethacin elicited an approximately 50% reduction in flow-dependent dilation, whereas their combined administration eliminated the responses in both groups. In arterioles of 12-week-old WKY, flow-induced dilation became significantly greater (maximum, 46.1+/-2.3 microm) than responses of arterioles of 4-week-old WKY and 12-week-old SHR (maximum, 18.3+/-5. 9 microm), which shifted only the shear stress-diameter curve of the 12-week-old WKY significantly to the left. Also, at 12 weeks of age, flow-dependent dilation of arterioles from SHR is mediated solely by PGs. Thus, shear stress-induced arteriolar dilation is mediated by NO and PGs in 4-week-old WKY and SHR. With aging, the release of NO and PGs increases in normotensive rats, whereas the contribution of NO to the regulation of shear stress disappears in 12-week-old SHR, which suggests that this change is probably caused by the increase in intraluminal pressure as hypertension develops.

Topics: Aging; Animals; Arterioles; Hypertension; Indomethacin; Male; Nitric Oxide; Nitroarginine; Prostaglandins; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Stress, Mechanical; Vasodilation

The tension in isolated ring preparations of the thoracic aortae from Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) was measured isometrically to study the differences in testosterone-induced relaxation between WKY and SHR aortic rings. Testosterone (9 to 300 micromol/L) induced a concentration-dependent relaxation in both WKY and SHR aortic rings, and the relaxation induced by testosterone was greater in SHR than WKY. The relaxation induced by testosterone was significantly reduced by denudation of endothelium in SHR but not WKY. Indomethacin, an inhibitor of cyclooxygenase, and N(G)-nitro-L-arginine, an inhibitor of nitric oxide (NO) synthase, showed little influence on the relaxation induced by testosterone in both WKY and SHR aortic rings. Glibenclamide, a selective inhibitor of ATP-sensitive potassium channels, significantly reduced the relaxation induced by testosterone in both WKY and SHR aortic rings, although the extent of reduction was greater in WKY than SHR. On the other hand, 4-aminopyridine, a selective inhibitor of voltage-dependent potassium channels, and tetraethylammonium, an inhibitor of calcium-activated potassium channels, significantly reduced the relaxation induced by testosterone in SHR but not WKY. These results suggest that the mechanisms of testosterone-induced vasorelaxation in both WKY and SHR involve, in part, ATP-sensitive potassium channels in the thoracic aortae and that in SHR aortic rings, testosterone may release endothelium-derived substances that may cause hyperpolarization of the cells by a mechanism that involves potassium channels. Moreover, the data show differences between WKY and SHR in the function of ATP-sensitive, voltage-dependent, and calcium-activated potassium channels.

Topics: 4-Aminopyridine; Acetylcholine; Animals; Aorta, Thoracic; Cyclooxygenase Inhibitors; Dose-Response Relationship, Drug; Glyburide; Hypertension; Hypoglycemic Agents; In Vitro Techniques; Male; Muscle Relaxation; Muscle, Smooth, Vascular; Nitroarginine; Nitroprusside; Potassium Channels; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Testosterone; Tetraethylammonium; Vasodilator Agents

Previously we found that flow-induced arteriolar dilation in male spontaneously hypertensive rats (SHR) is significantly impaired, due to the absence of the nitric oxide (NO)-mediated portion of the response, resulting in an elevation of maintained wall shear stress. Since estrogen has been shown to affect NO-mediated responses, we hypothesized that in female SHR (fSHR) the NO-mediated portion of flow-induced responses is preserved. Gracilis muscle arterioles (approximately 45 to 55 microm) from 12-week-old fSHR, ovariectomized fSHR (OV fSHR), or ovariectomized and supplemented with estrogen fSHR (OVE fSHR) were isolated, cannulated, and pressurized at 80 mm Hg of perfusion pressure. Arteriolar dilations elicited by step increases in perfusate flow from 0 to 25 microL/min were significantly less (by approximately 30%) in OV fSHR compared with fSHR and OVE fSHR (delta19.4+/-1.5 versus 26.0+/-0.9 and 26.8+/-2.0 microm, respectively at maximum flow rate). Inhibition of prostaglandin synthesis with indomethacin elicited a approximately 50% reduction in flow-dependent dilation in all three groups of rats. N(omega)-nitro-L-arginine (L-NNA) significantly inhibited flow-induced responses in arterioles of fSHR and OVE fSHR (by approximately 50%) but not in those of OV fSHR. Constrictions to norepinephrine (10(-7)-3 x 10(-7) mol/L) were significantly greater (up to approximately 40%) in arterioles of OV fSHR compared with those of fSHR and OVE fSHR; these differences, however, were abolished in the presence of L-NNA. In conclusion, estrogen seems to preserve the NO-mediated portion of flow/shear stress-induced dilation in female hypertensive rats resulting in a lower maintained wall shear stress in female than in male SHR. The lower wall shear stress may contribute to the mechanisms by which estrogen lowers systemic blood pressure and the incidence of cardiovascular diseases in women.

Topics: Animals; Arterioles; Blood Pressure; Body Weight; Estradiol; Estrogen Replacement Therapy; Female; Heart Rate; Hypertension; In Vitro Techniques; Indomethacin; Male; Muscle, Skeletal; Muscle, Smooth, Vascular; Nitric Oxide; Nitroarginine; Organ Size; Ovariectomy; Rats; Rats, Inbred SHR; Sex Characteristics; Stress, Mechanical; Uterus; Vasodilation

Hypertension has been linked to an impaired dilator function of the coronary microvascular endothelium in vivo. However, the profile and mechanism of this dysfunction remain obscure. Thus, this study compared diameter responses to acetylcholine (ACH), bradykinin (BKN), and substance P (SP) between coronary microvessels (i.d.=106+/-4 microm) dissected from left ventricles of normotensive and hypertensive Dahl rats (Dahl-NT and Dahl-HT, respectively). Vessels were cannulated and pressurized on glass pipettes at 80 mm Hg, and internal diameters were monitored by videomicroscopy. Coronary microvessels from Dahl-NT and Dahl-HT showed similar dilator responses to ACH (100 pmol/L to 10 micromol/L), with maximal diameter increases of 63+/-5 microm and 63+/-7 microm, respectively (n=31,17). However, only vessels from Dahl-NT showed dilator responses to SP (10 fmol/L to 1 nmol/L) and BKN (100 fmol/L to 10 nmol/L). All dilator responses persisted after N-nitro-L-arginine (10 micromol/L) or indomethacin (10 micromol/L), but were blunted after inhibition of cytochrome P450 by 10 micromol/L octadecynoic acid (n=6-8). These results suggest that: (1) coronary microvessels from Dahl-HT show a unique pattern of endothelial impairment, whereby ACH-induced relaxations persist at a time when dilator responses to SP and BKN are severely blunted, and (2) a cytochrome P450 product, rather than nitric oxide or prostacyclin, may partly mediate the vasodilator responses to ACH, SP and BKN.

Topics: Acetylcholine; Animals; Bradykinin; Coronary Vessels; Cytochrome P-450 Enzyme Inhibitors; Diet, Sodium-Restricted; Dose-Response Relationship, Drug; Endothelium, Vascular; Fatty Acids, Unsaturated; Hypertension; In Vitro Techniques; Indomethacin; Male; Microcirculation; Nitroarginine; Rats; Rats, Inbred Strains; Sodium, Dietary; Substance P; Vasodilation

In borderline hypertensive rats (BHR), behavioral stress produces hypertension, which has been attributed to increases in sympathetic nervous system activity and peripheral changes in vascular structure. However, the mechanisms mediating development of stress-induced hypertension have not been well defined. Experiments were designed to determine hemodynamic effects and changes in small mesenteric artery (approximately 300 microns) vascular reactivity in response to 10 days of air-jet stress (2 h/day) in BHR and in Wistar-Kyoto (WKY) rats. The acute stress-induced increase in mean arterial pressure (AP) was impaired in WKY rats compared with BHR on day 1, and habituation developed to the increase in AP in BHR, but not WKY rats. Conversely, WKY rats adapted to the stress-induced tachycardia to a larger extent than BHR. The mechanisms mediating endothelium-dependent relaxation to acetylcholine (ACh) were altered in small mesenteric arteries isolated from WKY rats and BHR after 10 days of air-jet stress. Inhibition of nitric oxide synthase activity had a significantly larger inhibitory effect on ACh-induced relaxation in vessels from stressed compared with control BHR. Also, cyclooxygenase products contributed to ACh-induced relaxation of small mesenteric arteries from stressed WKY rats, but not control WKY rats. Endothelium-independent relaxation to nitroprusside was impaired in vessels from stressed WKY rats, but not stressed BHR. Finally, contraction to phenylephrine was impaired in vessels from stressed BHR, but not WKY rats. In conclusion, changes in vascular reactivity induced by air-jet stress appear to correlate with, and may contribute to, the differential hemodynamic adaptations to stress observed in WKY rats and BHR.

Topics: Acetylcholine; Animals; Behavior, Animal; Blood Pressure; Enzyme Inhibitors; Female; Heart Rate; Hemodynamics; Hypertension; Male; Mesenteric Arteries; Nitric Oxide Synthase; Nitroarginine; Nitroprusside; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Stress, Physiological; Vasodilation

Unopposed actions of vasoconstrictors, such as angiotensin, play an important role in the effects of chronic nitric oxide synthase (NOS) inhibition. In this study, it is hypothesized that endothelin (ET), another important vasoconstrictor, may also play a role in the development of hypertension and renal lesions during chronic NOS inhibition. The ET(A) receptor was blocked with A-127722 during chronic NOS inhibition with Nomega-nitro-L-arginine (L-NNA), a potent NOS inhibitor without antimuscarinic action. Male Sprague Dawley rats were treated for 3 wk with L-NNA (40 mg/kg per d), L-NNA (40 mg/kg per d) + A-127722 (30 mg/kg per d), or remained untreated (control). In preliminary experiments, L-NNA (40 mg/kg per d) had been found to cause the maximum increase of systolic BP and a 35% decrease in renal NOS activity. Three weeks of L-NNA treatment resulted in a marked rise in systolic BP (240+/-4 versus control 151+/-7 mmHg; P < 0.01), proteinuria (209+/-46 versus control 27+/-3 mg/d; P < 0.01), and a fall in GFR (1.41+/-0.16 versus control 2.23+/-0.19 ml/min; P < 0.05). Renal morphology showed severe vascular injury, characterized by focal adhesion and infiltration of mononuclear cells into the intima and media of preglomerular arteries and arterioles. This was sometimes associated with necrosis of the media and partial or total obstruction of the lumen with thrombotic material. Ischemic glomeruli were also present. Tubulointerstitial damage was moderate and accompanied by an influx of monocytes and macrophages. A-127722 administered simultaneously with L-NNA completely prevented the increase in proteinuria (39+/-8 mg/d) and glomerular ischemia. Vascular injury, tubulointerstitial damage, and the increase in systolic BP (191+/-6 mmHg) were partially prevented. The protective effects of ET(A) receptor blockade suggest that ET has hemodynamic as well as nonhemodynamic effects in the cascade of events following chronic NOS inhibition.

Topics: Animals; Atrasentan; Blood Pressure; Dose-Response Relationship, Drug; Endothelin Receptor Antagonists; Enzyme Inhibitors; Hypertension; Kidney; Male; Nitric Oxide Synthase; Nitroarginine; Pyrrolidines; Rats; Rats, Sprague-Dawley; Receptor, Endothelin A; Time Factors

Experiments were performed in anesthetized male Sprague-Dawley rats to determine whether increased nitric oxide (NO) activity during the development of hypertension exerts a protective effect on renal cortical blood flow (CBF) and medullary blood flow (MBF). The effects of acute NO synthase inhibition on renal function and on CBF and MBF, measured by laser-Doppler flow probes, were evaluated in control and ANG II-infused hypertensive rats, prepared by the infusion of ANG II at a rate of 65 ng/min via osmotic minipumps implanted subcutaneously for 13 days. In normotensive rats (n = 8), intravenous infusion of N omega-nitro-L-arginine (NLA; 20 micrograms.100 g-1.min-1) decreased CBF by 21 +/- 4% and MBF by 49 +/- 8% and increased blood pressure from 118 +/- 1 to 140 +/- 2 mmHg. In ANG II-infused rats (n = 7), CBF and MBF decreased by 46 +/- 5% and 25 +/- 6%, respectively, during infusion of NLA. Arterial pressure increased from 160 +/- 5 to 197 +/- 7 mmHg, which was a greater absolute increase than in normotensive controls. Basal renal blood flow (RBF), estimated from p-aminohippurate clearance and hematocrit, was similar in both the control (6.0 +/- 0.5 ml.min-1.g-1) and hypertensive (6.0 +/- 0.6 ml.min-1.g-1) rats. However, NLA-induced reductions in RBF averaged 60 +/- 5% in the hypertensive rats, compared with 31 +/- 9% observed in control rats. GFR in control (0.97 +/- 0.03 ml.min-1.g-1) and hypertensive rats (0.78 +/- 0.12 ml.min-1.g-1) decreased to a similar extent during the first 30-min period of NLA infusion. GFR returned toward control levels in control rats; in contrast, GFR remained significantly decreased in the ANG II-infused rats (0.58 +/- 0.11 ml.min-1.g-1). Basal urinary sodium excretion (0.2 +/- 0.08 mueq.min-1.g-1), fractional excretion of sodium (0.3 +/- 0.13%), and urine flow (4.9 +/- 0.39 microliters.min-1.g-1) in hypertensive rats did not increase significantly after NLA treatment as occurred in normotensive controls. These data suggest that a compensatory increase in nitric oxide activity partially counteracts the vasoconstrictor influence of elevated ANG II levels to regulate renal hemodynamics and maintain cortical perfusion in the renal circulation.

Topics: Angiotensin II; Animals; Enzyme Inhibitors; Hypertension; Kidney; Laser-Doppler Flowmetry; Male; Nitric Oxide; Nitroarginine; Rats; Rats, Sprague-Dawley; Renal Circulation

1. The endothelium contributes substantially to the modulation of myogenic tone in coronary arteries from spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY). This study has addressed the contributions of endothelium-derived nitric oxide and cyclo-oxygenase products to this modulation in small coronary arteries (approximately 200 microns internal diameter) from 20-week-old SHR and WKY under pressurized, no-flow conditions in an arteriograph. 2. Active pressure-diameter relationships were uninfluenced by the cyclo-oxygenase inhibitor indomethacin (10 mumol/l) in either rat strain. In the presence of indomethacin and the nitric oxide synthase inhibitor N omega-nitro-L-arginine (L-NNA, 0.1 mmol/l), coronary arteries from SHR and WKY generated significantly greater myogenic tone. This increase in tone was similar in both strains. 3. In endothelium-denuded arteries, indomethacin and L-NNA did not influence tone. 4. Therefore, these results demonstrate that endothelium-derived nitric oxide is basally released to attenuate SHR and WKY coronary artery myogenic tone, whereas endothelium-derived cyclo-oxygenase products have no net vasoactive influence. Additionally, these data suggest that basal nitric oxide-mediated relaxation is normal in SHR coronary arteries and is therefore unlikely to be a pathogenic mechanism in this animal model of hypertension.

Topics: Animals; Coronary Vessels; Cyclooxygenase Inhibitors; Endothelium, Vascular; Enzyme Inhibitors; Hypertension; Indomethacin; Male; Muscle, Smooth, Vascular; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Vasoconstriction; Vasodilation

1. Endothelium-dependent acetylcholine-mediated relaxations of small coronary arteries (approximately 200 microns internal diameter) from 20 weeks old spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) controls were compared under pressurized no-flow conditions after the development of myogenic tone or constriction with the thromboxane A2 mimetic U46619. 2. Relaxations of WKY and SHR arteries following development of myogenic tone did not differ and were not significantly influenced by indomethacin alone (10 mumol/l) or in combination with N omega-nitro-L-arginine (L-NNA, 0.1 mmol/l). Maximum relaxations were significantly attenuated by 30 mmol/l K+ in the SHR, from 85 +/- 7% (n = 11) to 20 +/- 8% (n = 8), P < 0.001, and in the WKY from 86 +/- 5% (n = 9) to 39 +/- 14% (n = 8), P < 0.01. 3. Relaxations following constriction with U46619 were also similar in both rat strains. Maximum relaxations were 50 +/- 11% (n = 8) in SHR and 60 +/- 7% (n = 6) in WKY. Indomethacin did not influence these relaxations. The combination of indomethacin and L-NNA attenuated relaxations in WKY (P < 0.01), but in the SHR the attenuation did not achieve statistical significance (P = 0.07) compared with controls; the maximum responses were reduced to 25 +/- 7% (n = 8) and 14 +/- 11% (n = 6) in the SHR and WKY respectively, but only in the WKY was this reduction significant (P < 0.05). 4. These data demonstrate that, under control conditions, SHR and WKY coronary arteries relax equally effectively, regardless of mode of contraction, and also that the mechanism of acetylcholine-mediated relaxation differs according to the mode of contraction. Acetylcholine relaxes myogenic tone by a K(+)-sensitive mechanism in both WKY and SHR, consistent with a role for endothelium-derived hyperpolarizing factor; NO contributes substantially to the relaxation of U46619-induced tone by acetylcholine in the WKY, but to a diminished extent in the SHR. 5. These data indicate that the choice of vasoconstrictor agent is of critical concern when assessing mechanisms of endothelium-dependent relaxation and abnormalities thereof in hypertension.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Acetylcholine; Animals; Coronary Vessels; Cyclooxygenase Inhibitors; Endothelium, Vascular; Enzyme Inhibitors; Hypertension; Indomethacin; Male; Muscle, Smooth, Vascular; Nitroarginine; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Vasoconstriction; Vasoconstrictor Agents; Vasodilation

The present study was conducted to determine the contribution of nitric oxide to angiotensin II (Ang II) reactivity of afferent and efferent arterioles from Ang II-infused hypertensive rats. Experiments were performed in vitro with the blood-perfused juxtamedullary nephron technique in kidneys harvested from hypertensive Sprague-Dawley rats (181+/-1 mm Hg) that had received 60 ng/min Ang II subcutaneously for 13 days. Superfusion with 0.1, 1, and 10 nmol/L Ang II reduced afferent arteriolar diameter (18.1+/-0.6 microm; n=12) by 10.0+/-0.7%, 28.1+/-1.7%, and 52.8+/-1.9%, respectively, and efferent arteriolar diameter (17.2+/-1.4 microm; n=8) decreased by 9.3+/-0.7%, 27.0+/-1.2%, and 50.4+/-1.6%, respectively. Nitric oxide synthase inhibition with 100 micromol/L N(omega)-nitro-L-arginine (NLA) reduced resting afferent and efferent arteriolar diameters to 14.7+/-0.4 and 14.3+/-1.2 microm, respectively, and enhanced afferent but not efferent arteriolar reactivity to Ang II. The enhanced afferent arteriolar reactivity to Ang II was eliminated by addition of the nitric oxide donor S-nitroso-N-acetylpenicillamine (SNAP, 10 micromol/L), which reversed the NLA-induced decrease in diameter. Addition of 10 micromol/L SNAP, without NLA, blunted efferent but not afferent arteriolar reactivity to Ang II. Afferent (n=7) and efferent arteriolar diameters (n=6) decreased by 48.5+/-2.2% and 41.0+/-1.9%, respectively, in response to 10 nmol/L Ang II. These results suggest that in this model of hypertension, maintained nitric oxide production in afferent arterioles counteracts the enhanced afferent arteriolar reactivity that occurs in Ang II-induced hypertension.

Topics: Angiotensin II; Animals; Arterioles; Data Interpretation, Statistical; Enzyme Inhibitors; Hypertension; In Vitro Techniques; Kidney; Male; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Penicillamine; Rats; Rats, Sprague-Dawley; Time Factors

The factors responsible for the development of hypertension during chronic activation of intrarenal V1 receptors are unknown. We therefore tested whether medullary interstitial infusion of the selective V1-receptor agonist [Phe2,Ile3,Orn8]vasopressin (V1 agonist) influences renal antihypertensive mechanisms initiated by increased renal perfusion pressure (RPP). In intact anesthetized rabbits, the V1 agonist (10 ng . kg-1 . min-1) reduced medullary perfusion by 36 +/- 7%, whereas cortical perfusion was reduced by only 14 +/- 2%. An extracorporeal circuit was used to increase RPP in a stepwise manner from 65 to 85, 110, 130, and 160 mmHg for consecutive 20-min periods. Increased RPP reduced mean arterial pressure by 35 +/- 8% in vehicle-treated rabbits, but by only 10 +/- 3% in V1 agonist-treated rabbits. Simultaneously, pressure-diuresis-natriuresis was induced; urine flow and sodium excretion increased similarly in the two groups of rabbits, but hematocrit did not change. We suggest that the depressor response to increased RPP is mainly due to release of a putative renal medullary depressor hormone (RMDH). Suppression of the release and/or actions of RMDH may therefore contribute to the hypertensive effect of chronic V1 receptor activation.

Topics: Analysis of Variance; Animals; Blood Pressure; Female; Homeostasis; Hypertension; Infusions, Intravenous; Infusions, Parenteral; Kidney Medulla; Male; Nitroarginine; Ornipressin; Perfusion; Rabbits; Receptors, Vasopressin; Renal Circulation

The effects of FR139317((R)2-[(R)-2-[(S)-2-[[1-(hexahydro-1H-azepinyl)]carb onyl] amino-4-methyl-pentanoyl] amino-3-[3-(1-methyl-1H-indoyl)]propionyl]-amino-3-(2-pyridyl)prop ionic acid), an endothelin ET(A) receptor antagonist, on systemic and renal haemodynamic responses and excretory responses to chronic or acute nitric oxide (NO) synthase inhibition with NG-nitro-L-arginine (NOARG) have been examined. An intravenous bolus injection of FR139317 (10 mg kg(-1)) to chronic NO-deficient hypertensive rats (2.74 mM NOARG in drinking water for 4 weeks) elicited only a slight decrease in mean arterial pressure (MAP), to the same extent as seen in normotensive control rats. Injection of this drug induced no alteration of the renal haemodynamics of this chronic hypertensive model. Urine formation in control rats was significantly reduced by administration of FR139317. No significant decrease in urine formation was observed in the chronic NO-deficient rats. Acute intravenous injection of NOARG (5 mg kg(-1)) induced a gradual and significant increase in MAP, with a significant decrease in renal blood flow. A slight but insignificant diuretic effect was observed. In animals pretreated with FR139317 (10 mg kg(-1) i.v.) NOARG induced a significantly less potent increase in MAP, whereas similar renal haemodynamic responses to NOARG were observed. In contrast to the FR139317-untreated group, urine formation tended to decrease after administration of NOARG. These results suggest that endothelin, via the ET(A) receptor, contributes to the systemic pressor response to acute NO synthase inhibition, although renal vasoconstriction and functional changes induced by acute NO synthase inhibition are independent of ET(A) receptor-related effects. These results imply that action of endothelin via the ET(A) receptor is not involved in the maintenance of sustained hypertension induced by chronic NO synthase inhibition.

Topics: Animals; Azepines; Endothelin Receptor Antagonists; Enzyme Inhibitors; Hemodynamics; Hypertension; Indoles; Injections, Intravenous; Male; Nitric Oxide Synthase; Nitroarginine; Rats; Rats, Sprague-Dawley; Receptor, Endothelin A; Renal Circulation; Urine

The alpha2-adrenoceptor function in mesenteric arteries of spontaneously hypertensive rats (SHR) was investigated by comparing membrane potential changes in response to adrenergic agonists in preparations from female SHR, Wistar-Kyoto (WKY) and normotensive Wistar rats (NWR). Resting membrane potential was found to be less negative in mesenteric arteries from SHR than in those from NWR and WKY. Apamin induced a decrease in the membrane potential of mesenteric artery rings without endothelium from NWR and WKY, but had no effects in those from SHR. Both UK 14,304 and adrenaline, in the presence of prazosin, induced a hyperpolarization that was significantly lower in de-endothelialized mesenteric rings from SHR than in those from NWR and WKY. In mesenteric rings with endothelium, however, similar hyperpolarization was observed in the three strains. In NWR mesenteric rings with endothelium the hyperpolarization induced by activation of alpha2-adrenoceptors was abolished by apamin, whereas in intact SHR mesenteric rings this hyperpolarization was slightly reduced by apamin and more efficiently reduced by Nomega-nitro-L-arginine. It is concluded that the activity of potassium channels coupled to alpha2-adrenoceptors is altered in the smooth muscle cells of SHR mesenteric arteries, contributing to their less negative membrane potential. On the other hand, the endothelial alpha2-receptors are functioning in mesenteric vessels from SHR and their stimulation induces a hyperpolarization mainly through the release of nitric oxide.

Topics: Adrenergic alpha-Agonists; Adrenergic alpha-Antagonists; Animals; Apamin; Biological Factors; Brimonidine Tartrate; Endothelium, Vascular; Enzyme Inhibitors; Female; Hypertension; In Vitro Techniques; Membrane Potentials; Mesenteric Arteries; Muscle, Smooth, Vascular; Nitric Oxide; Nitroarginine; Prazosin; Quinoxalines; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Receptors, Adrenergic, alpha-2

Cyclosporin-induced hypertension is a major complication of immunosuppression in transplant recipients but its pathophysiology is only partly understood. Cyclosporin reduces endothelium-dependent vasodilation and increases endothelin synthesis and release, which may contribute to this hypertension. We examined the effects of: (1) nitric oxide enhancement with L-arginine administration and antagonism with N-nitro-L-arginine; and (2) chronic endothelin receptor blockade with the non-peptide endothelin receptor antagonist, bosentan, in two animal models of cyclosporin-induced hypertension. Cyclosporin, administered daily to female Wistar rats (10 mg/kg per day for 30 days, s.c.) and to marmosets (30 mg/kg per day for 20 days, p.o.) significantly elevated tail cuff systolic blood pressure (BP). L-arginine (250 mg/kg, in saline, i.p.), N-nitro-L-arginine (25 mg/kg, in saline, i.p.), bosentan (100 mg/kg, in arabic gum, p.o.) or vehicle were given daily to the rats during the last week of cyclosporin treatment. Marmosets received L-arginine (300 mg/kg, in water, p.o.), bosentan (100 mg/kg/day in arabic gum, p.o.) or vehicle for the last 7 days of cyclosporin treatment. L-arginine, but not saline alone significantly lowered BP in the cyclosporin-hypertensive rats from 129 +/- 2 mm Hg to 122 +/- 3 mm Hg (P < 0.05), and cyclosporin-hypertensive marmosets from 156 +/- 2 mm Hg to 139 +/- 4 mm Hg (P < 0.01). NOLA significantly increased systolic BP in cyclosporin-treated (from 133 +/- 2 mm Hg at week 3 to 142 +/- 3 mm Hg, P < 0.05) and control rats (from 124.0 +/- 2 mm Hg to 134 +/- 2 mm Hg, P < 0.05) indicating that nitric oxide synthesis in cyclosporin-hypertensive rats could be further antagonised. Bosentan, but not arabic gum alone, also lowered BP in the cyclosporin-hypertensive rats from 134 +/- 1 mm Hg to 122 +/- 3 mm Hg (P < 0.01), and cyclosporin-hypertensive marmosets from 156 +/- 2 mm Hg to 139 +/- 4 mm Hg (P < 0.01). These results support the roles of both increased endothelin synthesis and decreased nitric oxide activity in the pathogenesis of cyclosporin A-induced hypertension.

Topics: Animals; Antihypertensive Agents; Arginine; Blood Pressure; Bosentan; Callithrix; Cyclosporine; Enzyme Inhibitors; Female; Hypertension; Immunosuppressive Agents; Male; Nitrates; Nitric Oxide; Nitrites; Nitroarginine; Rats; Rats, Wistar; Sulfonamides; Systole

1. Previous studies have indicated that younger hypertensive subjects may have abnormal endothelium-dependent relaxation, which could contribute to the elevated peripheral resistance seen in established hypertension. This study was designed to examine the functional behaviour of the endothelium of small arteries from elderly hypertensive and normotensive subjects. 2. Resistance arteries were obtained from gluteal biopsies taken under local anaesthesia in 28 subjects of mean age 70 (range 60-76) years, and studied in an isometric myograph. Eighteen subjects had untreated essential hypertension, and 10 were normotensive. 3. After measurement of the contractile response to noradrenaline, relaxation responses to a variety of endothelium-dependent (acetylcholine and bradykinin) and endothelium-independent (iloprost and sodium nitroprusside) mechanisms were assessed in vessels precontracted with noradrenaline. Endothelium-dependent responses were also studied after incubation with NG-nitro-L-arginine to inhibit nitric oxide synthase. 4. There were no significant differences in the contraction or relaxation responses between elderly subjects with or without high blood pressure. Inhibition of nitric oxide synthase prevented any relaxation with acetylcholine and significantly attenuated the relaxation with bradykinin. Near-complete relaxation was however achieved with the endothelium-independent vasodilator sodium nitroprusside. 5. Hypertension in elderly subjects is not associated with a reduction in endothelial vasodilating function in the subcutaneous vessels of the gluteal region compared with age-matched normotensive controls. The results of this study do not support the hypothesis of a defect of resistance artery endothelium-dependent relaxation in the pathophysiology of hypertension in the elderly.

Topics: Acetylcholine; Aged; Arteries; Bradykinin; Endothelium, Vascular; Female; Humans; Hypertension; Iloprost; In Vitro Techniques; Male; Middle Aged; Nitric Oxide Synthase; Nitroarginine; Nitroprusside; Norepinephrine; Vascular Resistance; Vasodilator Agents

The aim of the present study was to find out whether brain nitroxidergic system may be involved in modulation of central cardiovascular effects of arginine vasopressin (AVP) in normotensive (WKY) rats and whether its regulatory effects are altered in spontaneously hypertensive (SHR) rats. Two series of experiments were performed on conscious WKY and SHR rats instrumented with the lateral cerebral ventricle (i.c.v.) cannula and with the femoral arterial catheters. In Series 1 (10 WKY, 7 SHR rats), i.c.v. application of 2.3 nmol (0.5 microg) of N(G)-nitro-L-arginine (L-NNA), an inhibitor of NO synthesis, did not significantly affect baseline arterial blood pressure (MAP) and heart rate (HR). In WKY but not in SHR, i.c.v. administration of 5.8 nmol (1 microg) of L-arginine (L-ARG) elicited a small, significant decrease of MAP (P < 0.05) which could be reversed by i.c.v. pretreatment with L-NNA. In Series 2 (7 WKY, 8 SHR), administration of 10 pmol of AVP (10 ng) resulted in significant pressor effect in both strains; MAP increase being significantly greater in SHR than in WKY rats (P < 0.05). I.c.v. pretreatment with L-NNA significantly intensified the pressor response to centrally applied AVP both in WKY (P < 0.01) and in SHR (P < 0.01) rats; the maximum increase of blood pressure to combined administration of L-NNA and AVP being significantly greater in SHR than in WKY rats. The results indicate existence of an interaction between the central vasopressinergic and nitroxidergic system in blood pressure regulation. It is suggested that centrally released AVP increases availability of nitric oxide in the brain cardiovascular regions, whereas NO plays a compensatory role by reducing central pressor effect of AVP. Effectiveness of this compensatory mechanism is enhanced in the SHR rats.

Topics: Animals; Arginine Vasopressin; Blood Pressure; Brain; Drug Synergism; Hypertension; Injections, Intraventricular; Nitroarginine; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Reference Values

Long-term inhibition of nitric oxide synthase (NOS) by substituted arginine analogues has previously been shown to induce systemic hypertension in several animal species; however, the precise mechanisms for the elevated blood pressure remain unclear. We hypothesized that a portion of the hypertensive response to arginine analogues was due to direct inhibition of endothelial NOS and resultant functional alterations in the vasculature that contribute to elevated systemic resistance. Adult Sprague-Dawley rats were treated for 2 weeks with an arginine analogue, N omega Nitro-L-arginine (L-NNA), alone or in combination with the angiotensin converting enzyme (ACE) inhibitor quinapril. Next, thoracic aortas were removed, cut into rings and suspended in isolated tissue baths for measurement of contractile force in response to vasoactive drugs. Our results showed that oral L-NNA treatment significantly elevated systolic blood pressure in rats that was completely prevented by quinapril. Furthermore, L-NNA treatment increased endothelium-dependent and -independent contractility and attenuated endothelium-dependent vasodilation in the thoracic aorta. These functional alterations were also attenuated by quinapril treatment. Therefore, long-term L-NNA-induced hypertension in rats is associated with enhanced vascular reactivity due both to direct inhibition of endothelial NOS and to stimulation of the renin-angiotensin system.

Topics: Angiotensin-Converting Enzyme Inhibitors; Animals; Aorta; Blood Pressure; Body Weight; Enzyme Inhibitors; Hypertension; In Vitro Techniques; Isoquinolines; Male; Nitroarginine; Quinapril; Rats; Rats, Sprague-Dawley; Tetrahydroisoquinolines; Vasomotor System

Several mechanisms are known to participate in cold-induced hypertension, but no information exist on the role of the nitric oxide (NO). In the present study, we assessed the participation of nitric oxide in cold-induced hypertension by means of inhibition of NO synthase. Experiments were performed in rats treated with N omega-nitro-L-arginine (L-NNA) injected i.p. at a dose of 25 mg/kg body weight twice a day for four consecutive days. Control animals received saline injections of the same volume. Two days before the experiment, the femoral artery was cannulated for blood pressure recording. Arterial blood pressure was measured at 25 degrees C for 30 min (control period), followed by a 3.5 hour period at 4 degrees C (cold exposure) and, eventually, a last 3 hour period after removal from cold (back to 25 degrees C). In control animals, at 25 degrees C, mean arterial blood pressure was 112.5+/-3.6 mmHg and heart rate was 380+/-3.5 bpm. L-NNA treatment caused an increase in blood pressure to 155.0+/-3.5 mmHg (P<0.01) and in heart rate to 410+/-6.0 bpm (P<0.05). Exposure to cold caused blood pressure to increase up to 131.5+/-3.6 mmHg (P<0.05) in the control group, whereas no significant change could be measured in treated animals. Recovery from cold exposure led to a decrease in blood pressure in control animals, but not in treated animals. These results indicate that NO plays a role in the development of cold-induced elevation of blood pressure.

Topics: Animals; Cold Temperature; Hypertension; Male; Nitric Oxide; Nitroarginine; Rats; Rats, Wistar

We have recently reported in normal isolated-perfused rat lungs that low basal tone appears to be regulated by nitric oxide (NO)-dependent and -independent mechanisms of soluble guanylate cyclase activation. In this study, we examined the role of NO in the regulation of pulmonary artery (PA) tone from rats with renin-dependent hypertension. Rats were made hypertensive by ligating the abdominal aorta above the left and below the right renal artery (aortic coarctation, AC). Mean arterial pressure significantly increased from 119 +/- 8.4 mmHg in control animals to 156 +/- 15 mmHg 7-14 days after AC surgery. PA pressures, however, remained unchanged (8.5 +/- 3.4 mmHg in control animals vs. 11 +/- 3.3 mmHg in AC animals). Hypoxic contractions in U-46619 precontracted isolated small PA (160-260 microns diameter) were significantly increased from 51 +/- 13 mg in the control group to 142 +/- 38 mg (P < or = 0.05) in AC animals. Nitro-L-arginine (NLA; 100 microM) contractions were also enhanced in the AC animal. The enhanced NLA response may correlate with an increase in endothelial cell NO synthase (NOS) as detected by Western blotting (132 +/- 28% of control; P < 0.05). These data suggest that, in this renin-dependent model of systemic hypertension, there is increased endothelial cell NOS activity that maintains low PA tone, preventing the lung from developing increased pressures.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Animals; Aorta, Abdominal; Aortic Coarctation; Blood Pressure; Endothelium, Vascular; Guanylate Cyclase; Hypertension; Hypoxia; In Vitro Techniques; Male; Muscle Contraction; Muscle Tonus; Muscle, Smooth, Vascular; Nitric Oxide Synthase; Nitroarginine; Prostaglandin Endoperoxides, Synthetic; Pulmonary Artery; Pulmonary Circulation; Rats; Rats, Sprague-Dawley; Regression Analysis; Renin; Thromboxane A2; Vasoconstrictor Agents

The role of the endothelium-derived relaxing factor (EDRF), nitric oxide (NO), in the withdrawal-induced antihypertensive phenomenon (WAP) of arginine vasopressin (AVP) was studied in conscious unrestrained rats implanted with femoral arterial catheters for the measurement of arterial blood pressure. Cessation of a 3-h intravenous infusion of AVP (20 ng.kg-1.min-1) was followed by a large and long-lasting fall in mean arterial blood pressure below preinfusion control values in spontaneously hypertensive rats (SHR; -47.5 +/- 6.4 mmHg; 1 mmHg = 133.3 Pa) but not in normotensive Wistar-Kyoto (WKY) and Sprague-Dawley (SD) control rats. Chronic treatment of normotensive SD rats with the NO synthesis inhibitor, N omega-nitro-L-arginine (L-NNA; 0.5 g.L-1 in drinking water for 2 weeks), resulted in sustained hypertension. Similar to the SHR model, a large fall in blood pressure (-37.8 +/- 7.7 mmHg) was observed in this model of hypertension following cessation of the AVP infusion. In SHR, inhibition of NO synthesis with L-NNA (0.05 g.L-1 in drinking water for 2 weeks) failed to attenuate the fall in blood pressure following withdrawal of AVP. Chronic treatment with the NO precursor, L-arginine (L-Arg; 1.25 g.L-1 in drinking water for 2 weeks), did not affect the amplitude or the time course of the WAP in SHR. The results indicate that the L-Arg/NO pathway is not essential to the expression of the WAP to AVP in the SHR.

Topics: Animals; Antihypertensive Agents; Arginine; Arginine Vasopressin; Blood Pressure; Enzyme Inhibitors; Hypertension; Male; Nitric Oxide; Nitroarginine; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Rats, Sprague-Dawley; Substance Withdrawal Syndrome; Vasoconstrictor Agents

Rat pregnancy is associated with a blunted response to vasocontrictors both in vivo and in vitro as well as a decrease in arterial pressure. We examined the influence of pregnancy on neurally induced vasoconstrictor and vasodilator responses of the isolated mesenteric arterial bed from normotensive Wistar and spontaneously hypertensive nonpregnant and 20-day pregnant rats and determined the possible role of nitric oxide (NO) in modulating these responses. MAP (mm Hg) in pregnant normotensive (98+/-1, n=13) and hypertensive (136+/-5, n=13) rats was lower (P<.05) than in nonpregnant controls (114+/-2, n=14, and 174+/-3, n=12, respectively). In isolated mesenteric arterial beds, electrical field stimulation (EFS; 34 V, 3 ms, 10-64 Hz) of perivascular nerves at basal tone induced a frequency-dependent increase in perfusion pressure that was significantly (P<.001) greater in preparations from hypertensive compared with normotensive rats. Pregnancy was associated with a significant decrease in the maximal vasoconstrictor response elicited by EFS in both normotensive and hypertensive groups compared with their nonpregnant controls. In phenylephrine-preconstricted mesenteric beds, EFS (60 V, 1 ms, 1-8 Hz) elicited a similar frequency-dependent decrease in perfusion pressure in normotensive and hypertensive groups, but pregnancy did not influence these responses. In the presence of the NO synthase inhibitor N(omega)-nitro-L-arginine (200 micromol/L), the maximal vasoconstrictor response induced by EFS was significantly (P<.001) augmented in both normotensive and hypertensive groups, and the differences observed between pregnant and nonpregnant groups were abolished. Responses to sodium nitroprusside were not affected by pregnancy, although they were greater in preparations from hypertensive rats. These results indicate that NO contributes to pregnancy-associated diminished vasoconstrictor response to sympathetic stimulation in the mesenteric arterial bed of both normotensive and hypertensive rats.

Topics: Animals; Female; Hypertension; Mesenteric Arteries; Nitric Oxide; Nitroarginine; Pregnancy; Pregnancy, Animal; Rats; Rats, Inbred SHR; Rats, Wistar; Sympathetic Nervous System; Vasoconstriction

1. Recent evidence suggests that nitric oxide (NO) modulates the contractile force of isolated cardiomyocytes in a biphasic manner. We sought to examine whether myocardial hypertrophy induced by long-term hypertension changes the effects of NO on myocardial contractility. 2. We used constant flow perfused non-paced Langendorff preparations of hearts of 3 months old Wistar rats (WIS, n = 23) and of stroke-prone spontaneously hypertensive rats (SHR) at the age of 10 months (SHR10, n = 16) and 15 months (SHR15, n = 8). Changes of left ventricular peak pressure (LVP), +dP/dt(max), -dP/dt(max), coronary perfusion pressure (CPP) and heart rate (HR) were recorded after infusion of noradrenaline (NA, 0.1 micromol l(-1)), glyceryl trinitrate (GTN, 1-100 micromol l(-1)), S-nitroso-N-acetyl-D,L-penicillamine (SNAP, 1-10 micromol l(-1)) and N(omega)-nitro-L-arginine (L-NOARG, 0.1-1 mmol l(-1)). 3. Long-term hypertension induced myocardial hypertrophy and an abnormal response to NA. The relative heart weight (in mg kg(-1)) increased from 2.95 +/- 0.04 (WIS) to 6.67 +/- 0.34 (SHR15), while the increase in +dP/dt(max) induced by NA was absent in SHR15. Hearts of SHR10 showed an intermediate response. 4. Both SNAP and GTN significantly increased LVP, +dP/dt(max) and -dP/dt(max) in hearts of WIS and of SHR. In WIS but not in SHR10, SNAP also increased HR. In SHR10 the lowest concentration of SNAP (1 micromol l(-1)) showed no effect on contractility but a significantly diminished reduction of CPP suggesting inactivation of extracellularly released NO in the coronary circulation of SHR. 5. L-NOARG significantly reduced contractility in hearts of WIS and of SHR to a similar extent. At a concentration of 1 mmol l(-1) L-NOARG also reduced HR. 6. These results suggests that positive inotropic effects of exogenous and endogenous NO are not changed in hypertension induced myocardial hypertrophy.

Topics: Animals; Blood Pressure; Cardiomegaly; Heart; Heart Rate; Hypertension; In Vitro Techniques; Male; Myocardial Contraction; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Nitroglycerin; Norepinephrine; Penicillamine; Rats; Rats, Inbred SHR; Rats, Wistar; S-Nitroso-N-Acetylpenicillamine; Stimulation, Chemical; Vasoconstrictor Agents; Vasodilator Agents; Ventricular Pressure

Diminished nitric oxide (NO) production has been implicated in the pathogenesis of salt-sensitive hypertension. We questioned whether such a defect is responsible for the malignant hypertension and nephrosclerosis in stroke-prone spontaneously hypertensive rats (SHRSP) fed a high-salt/stroke-prone diet (S) versus a regular diet (R). NO release from 30-minute incubates of cortex and outer and inner medulla were studied in SHRSP at 10, 12, and 16 weeks of age on the S diet versus R diet. SHRSP-S (n=16) exhibited a marked age-dependent increase in NO release, especially in the cortex. Increases were only modest in SHRSP-R (n=21). At 16 weeks, cortical NO was 93+/-25 versus 6+/-1 pmol/mg tissue in SHRSP-S versus SHRSP-R (P<.001). Immunohistochemical staining increased mostly for neuronal, slightly for endothelial, and negligibly for inducible isoforms of NO synthase and was predominantly in the cortex of SHRSP-S versus SHRSP-R. Despite similar hypertension in SHRSP-S versus SHRSP-R (mean arterial pressure, 174+/-7 versus 177+/-2 mm Hg), malignant nephrosclerosis was seen only in SHRSP-S, affecting 22+/-6% of glomeruli and 23+/-4 vessels per 100 glomeruli by 16 weeks. N omega-nitro-L-arginine (15 mg/kg per day) in SHRSP-S (n=6) abrogated the increase in cortical NO but further augmented the hypertension and accelerated lesion development. Wistar-Kyoto rats at 16 weeks on the R diet (n=8) had NO levels similar to those of SHRSP-R, showed increased cortical NO to only 28+/-10 pmol/mg on the S diet (n=9) (P<.05 versus SHRSP-S), but remained normotensive and lesion-free. We conclude that hypertension and lesion development in SHRSP are not due to deficient renal NO. Accelerated onset of malignant nephrosclerosis by NO synthase inhibition suggests that NO is protective in these animals, mitigating the effects of hypertension and S diet on renal pathology.

Topics: Aging; Animals; Blood Pressure; Cerebrovascular Disorders; Hypertension; Kidney Cortex; Kidney Glomerulus; Kidney Medulla; Male; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Renal Circulation; Sodium, Dietary

Increased vascular resistance during systemic nitric oxide synthase (NOS) inhibition is dependent on adrenergic vasoconstriction. This study tested the hypothesis that increased vascular sensitivity to adrenergic agonists contributes to this vasoconstriction. Superior mesenteric arteries and thoracic aortae from male Sprague-Dawley rats drinking water containing N omega-nitro-L-arginine (L-NNA; 14 days, 60 mg.kg-1.day-1) and control rats were-cut into helical strips, and endothelium was removed for contractile experiments. L-NNA arteries were more sensitive to UK-14304 (alpha 2-adrenergic agonist) and norepinephrine (NE), whereas responses to phenylephrine (PE) were not different concentration causing 50% maximal response (EC50), L-NNA vs. control: UK-14304, 0.071 vs. 0.71 mumol/l; NE, 1.15 vs. 9.95 nmol/l]. Yohimbine, an alpha 2-selective antagonist, caused a concentration-dependent inhibition of contraction to NE only in L-NNA arteries (EC50 = 6.3 vs. 1.6 nmol/l at 1 nmol/l yohimbine), whereas prazosin shifted NE curves similarly in arteries from both groups. Yohimbine (10 nmol/l) inhibited contractions to UK-14304 (EC50 = 59 mumol/l vs. 17 mumol/l) but not contractions to PE, whereas prazosin inhibited both. These data indicate that L-NNA-induced hypertension leads to increased sensitivity of prazosin-sensitive alpha 2-adrenoceptors, an upregulation that could cause the increased vasoconstrictor response to NE in this model of hypertension.

Topics: Adrenergic alpha-Agonists; Animals; Aorta, Thoracic; Blood Pressure; Body Weight; Brimonidine Tartrate; Enzyme Inhibitors; Hypertension; In Vitro Techniques; Male; Mesenteric Artery, Superior; Muscle Contraction; Muscle, Smooth, Vascular; Nitric Oxide Synthase; Nitroarginine; Norepinephrine; Phenylephrine; Quinoxalines; Rats; Rats, Sprague-Dawley; Receptors, Adrenergic, alpha-2; Systole; Vasoconstriction; Yohimbine

The purpose of these studies was to compare changes in conduit and resistance artery function in deoxycorticosterone-salt hypertensive rats. We hypothesized that if there was a common mechanism producing changes in vascular function in hypertension, then there would be similar alterations in reactivity of conduit and resistance arteries. Helically cut strips of common carotid artery were prepared for measurement of isometric force generation, and segments of small mesenteric arteries were pressurized for video dimension analysis. Sensitivity of arteries to phenylephrine and acetylcholine was determined. Carotid arteries from deoxycorticosterone-salt hypertensive rats were more sensitive to phenylephrine than arteries from control rats, whereas mesenteric resistance arteries from hypertensive rats were less sensitive to phenylephrine. In carotid arteries, endothelial denudation or incubation with N psi-nitro-L-arginine increased phenylephrine sensitivity in control rats to the level seen in deoxycorticosterone-salt rats. These manipulations had no effect on phenylephrine sensitivity in arteries from deoxycorticosterone-salt rats. In mesenteric resistance arteries, endothelium denudation normalized the depressed phenylephrine sensitivity in arteries from hypertensive rats but had no effect on arteries from normotensive rats. This depressed phenylephrine sensitivity in deoxycorticosterone-salt mesenteric arteries was not reversed by incubation with Npsi-nitro-L-arginine. Acetylcholine-induced relaxation was depressed in carotid arteries from deoxycorticosterone-salt hypertensive rats, and Npsi-nitro-L-arginine blocked these relaxations. In contrast, acetylcholine relaxation in the mesenteric arteries from normotensive and hypertensive rats did not differ. N psi-nitro-L-arginine slightly but significantly attenuated acetylcholine dilation only in mesenteric resistance arteries from the hypertensive rats. We conclude that qualitatively different changes in vasoconstrictor sensitivity to phenylephrine occur in carotid arteries and mesenteric resistance arteries of deoxycorticosterone-salt hypertensive rats. The increased phenylephrine sensitivity in carotid arteries in this model of hypertension is due to the loss of endothelium-derived nitric oxide production. In contrast, the decreased phenylephrine sensitivity in mesenteric resistance arteries from deoxy-corticosterone-salt rats is due to a non-nitric oxide-mediated influence of the endothelium that is absen

Topics: Acetylcholine; Animals; Arginine; Blood Pressure; Carotid Arteries; Desoxycorticosterone; Endothelium, Vascular; Hypertension; Male; Mesenteric Arteries; Muscle, Smooth, Vascular; Nitric Oxide Synthase; Nitroarginine; Nitroprusside; Phenylephrine; Rats; Rats, Wistar; Vasoconstrictor Agents; Vasodilator Agents

To examine the effects of different types of antihypertensive treatment on endothelium-dependent relaxation in resistance arteries from spontaneously hypertensive rats (SHRs).. Three-week-old SHRs were treated with the angiotensin converting enzyme (ACE) inhibitor perindopril (1 mg/kg/day) or quinapril (3 mg/kg/day) or the vasodilator hydralazine (50 mg/kg/day) or the calcium antagonist amlodipine (10 mg/kg/day). Control SHRs and Wistar-Kyoto (WKY) rats were treated with water. After 21 weeks rats were culled and mesenteric resistance arteries were mounted in a myograph. Relaxation responses to the endothelium-dependent vasodilators acetylcholine (ACh) and bradykinin were recorded before and after incubation with the nitric oxide synthase inhibitor NG-nitro-L-arginine (L-NOARG), as was the relaxation response to the nitric oxide donor sodium nitroprusside (SNP).. All drugs prevented the rise in blood pressure found in the untreated SHRs. ACh-induced relaxation was significantly impaired in the untreated SHRs compared with the WKY rats. Treatment with either ACE inhibitor prevented the development of this impaired response. ACE inhibitor treatment significantly increased the relaxation response to bradykinin. Despite lowering blood pressure, hydralazine or amlodipine had no effect on ACh- or bradykinin-induced relaxation. Responses to SNP were not different between untreated SHRs and WKY rats and were not affected by drug treatment.. Specific properties of certain antihypertensive drugs may play an important role in restoring endothelium-dependent relaxation in the small arteries that regulate peripheral resistance in the SHR.

Topics: Acetylcholine; Amlodipine; Animals; Antihypertensive Agents; Arginine; Bradykinin; Dose-Response Relationship, Drug; Endothelium, Vascular; Hydralazine; Hypertension; Indoles; Isoquinolines; Mesenteric Arteries; Nitroarginine; Perindopril; Quinapril; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Tetrahydroisoquinolines; Vasodilation

Experiments were conducted to compare the effects of intratubular inhibition [N omega-nitro-L-arginine (L-NNA)] of nitric oxide (NO) on the tubuloglomerular feedback (TGF) mechanism between anesthetized spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY) and between the Milan hypertensive (MHS) and the Milan normotensive (MNS) strains of rats. Changes in proximal tubular stop-flow pressure (Psf) in response to various loop of Henle perfusion rates and measurements of early proximal flow rate (EPFR) were used to characterize TGF. Maximal drop in Psf (delta Psf) were used to indicate TGF reactivity and the flow rate eliciting half-maximal delta Psf (turning point; TP) to indicate TGF sensitivity. Under control conditions, TGF sensitivity was significantly higher in SHR than in WKY, but, after L-NNA infusion, TP was decreased in WKY and not in SHR. L-NNA infusion increased delta Psf by 95% in WKY but to a lesser extent (by 26%) in SHR. In the same way, L-NNA decreased TP in MNS but not in MHS. The increase in delta Psf was 99% in MNS but only 32% in MHS. The EPFR reduction after TGF activation was significantly increased in WKY and MNS but relatively unchanged in SHR and MHS. The results show that the effect of intratubular NO synthase inhibition on TGF is impaired in both strains of hypertensive rats.

Topics: Animals; Capillaries; Feedback; Glomerular Filtration Rate; Hypertension; Kidney Glomerulus; Kidney Tubules; Kidney Tubules, Proximal; Male; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Pressure; Rats; Rats, Inbred SHR; Rats, Inbred Strains; Rats, Inbred WKY

Differences in alpha(2)-adrenoceptor-induced relaxation of the aorta between stroke-prone spontaneously hypertensive rats (SHRSP) and control normotensive Wistar Kyoto rats (WKY) were studied. Changes in the tension of ring preparations of the aortas were measured isometrically. Relaxation was observed in the preparations precontracted in the presence of ONO-11113, a thromboxane A(2) analogue. The alpha(2)-agonist clonidine and UK-14304 induced dose-dependent relaxation in both the WKY and SHRSP preparations. The relaxation was impaired in the SHRSP preparation. A modified sandwich experiment showed that the relaxing substance from the SHRSP endothelium was decreased. Acetylcholine (ACh) also induced dose-dependent relaxation, and the relaxation was impaired in the SHRSP preparations. alpha(2)-Agonists induced a greater degree of impairment in the relaxation than did ACh. The relaxation induced by alpha(2)-agonists and by ACh was blocked by N G-nitro-L-arginine (L-NNA). Indomethacin improved the relaxation induced by ACh but not that induced by alpha(2)-agonists in the SHRSP aortas. These results suggest that the impairment of relaxation by alpha(2)-agonists in SHRSP is not caused by the increase in the release of endothelium-derived contracting factor (EDCF) but by the reduction in the release of nitric oxide (NO). Alteration of the alpha(2)-adrenoceptors and/or the intracellular mechanism through which NO is synthesized by stimulation of the alpha(2)-adrenoceptors may be the cause of the reduction in relaxation.

Topics: Acetylcholine; Adrenergic alpha-2 Receptor Agonists; Adrenergic alpha-Agonists; Animals; Aorta; Brimonidine Tartrate; Endothelium, Vascular; Hypertension; Indomethacin; Nitroarginine; Quinoxalines; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Thromboxane A2; Vasodilation

This study investigated the effect of physical training on endothelial function in spontaneously hypertensive rats (SHR). After 3 months, in conscious trained- and untrained-SHR body weight, systolic blood pressure and heart rate were 220 +/- 6 g vs 271 +/- 9 g, 172 +/- 7 mmHg vs 210 +/- 8 mmHg and 314 +/- 10 vs. 348 +/- 12 beats/min, respectively. In vitro, the dose-response curves of norepinephrine in isolated intact aortic and mesenteric rings form the exercise trained-SHR were significantly lower than those from the untrained-SHR. With denuded preparations, norepinephrine concentration-response curves were shifted to the left both in the trained- and untrained-SHR. This shift in the trained-SHR exceeded that in the untrained-SHR. The vasodilator response to acetylcholine in the trained-SHR was significantly greater than that in the untrained-SHR. Either N omega-nitro-L-arginine (100 mumol/l) or methylene blue (10 mumol/l) inhibited acetylcholine-induced vasodilator effect in aorta of trained- and untrained-SHR, but not in mesenteric artery of trained-SHR. Tetraethylammonium (10 mmol/l) inhibited significantly the N omega-nitro-L-arginine and methylene blue-resistant relaxation in mesenteric artery of trained-SHR, but not only by indomethacin (10 mumol/l). Collectively, these data demonstrate that chronic exercise increases EDRF/EDHF production (presumably by increasing endothelial shear stress), and may contribute to the enhanced effects of post-exercise hypotension.

Topics: Acetylcholine; Animals; Aorta; Arginine; Blood Pressure; Dose-Response Relationship, Drug; Endothelium, Vascular; Enzyme Inhibitors; Heart Rate; Hypertension; Lipoproteins; Male; Mesenteric Arteries; Methylene Blue; Nitroarginine; Nitroglycerin; Norepinephrine; Physical Exertion; Rats; Rats, Inbred SHR; Vasodilation; Vasodilator Agents

We evaluated the response of pial arterioles to L-arginine in anesthetized normotensive rats and spontaneously hypertensive rats equipped with a closed cranial window. Topical application of 10(-6)-10(-4) mol/l L-arginine, which is known to be the endogenous substrate for the synthesis of nitric oxide, induced dose-dependent arteriolar vasodilation. The response was more pronounced in hypertensive than in normotensive rats (at the concentration of 10(-4) mol/l L-arginine: 18.3 +/- 3.3% vs. 6.7 +/- 1.7%, respectively, means +/- S.E.). The stereoisomer D-arginine had no effect in hypertensive rats. Topical application of the nitric oxide synthase inhibitor N-nitro-L-arginine converted L-arginine-induced dilation to constriction in normotensive and hypertensive rats. The cyclooxygenase inhibitor indomethacin (5 micrograms/ml cerebrospinal fluid) also blocked the dilation in both strains. Photochemical endothelial injury blocked L-arginine-induced dilation in normotensive rats, but only partly antagonized the response in hypertensive animals. Intravenous or topical pretreatment with the free radical scavenger superoxide dismutase significantly reduced the dilating response to 10(-4) mol/l L-arginine in hypertensive rats. Superoxide dismutase did not significantly change the response to L-arginine in normotensive animals. It is concluded that nitric oxid formation in the endothelium and liberation of cyclooxygenase products cause L-arginine-induced dilation in normotensive rats. While nitric oxide and cyclooxygenase products are also involved in L-arginine-induced dilation in spontaneously hypertensive rats, superoxide radicals contribute to the enhanced response in this strain. This mechanism appears to be specific for the hypertensive animals and is only partly dependent on an intact endothelium.

Topics: Amino Acid Oxidoreductases; Animals; Arginine; Arterioles; Blood Pressure; Brain; Endothelium; Hypertension; Indomethacin; Male; Nitric Oxide Synthase; Nitroarginine; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Superoxide Dismutase; Vasodilation

The purpose of this study is to elucidate the role of parathyroid hormone (PTH) in the development of hypertension in young spontaneously hypertensive rats (SHR). Parathyroidectomy (PTX) or sham surgery was performed on 6-week-old male SHR, and 3 weeks later human PTH (hPTH) or saline was infused subcutaneously over 2 weeks using a minipump. PTX significantly attenuated the development of hypertension and reduced serum vitamin-D concentrations. PTX also augmented the depressor response to acetylcholine before N-nitro-L-arginine (L-NNA), although it remained unchanged after L-NNA. The cardiovascular reactivity to exogenous noradrenaline and angiotensin II was not affected by PTX. The chronic administration of hPTH reversed these effects. We conclude that PTH plays an important role in the development of hypertension, through modulating the release of endothelium-derived relaxing factor, in young SHR.

Topics: Acetylcholine; Analysis of Variance; Animals; Arginine; Blood Pressure; Drug Synergism; Hypertension; Ibuprofen; Infusion Pumps; Male; Nitroarginine; Parathyroid Hormone; Parathyroidectomy; Rats; Rats, Inbred SHR

We tested the hypotheses that maintaining the activity of nitric oxide by L-arginine infusion would counteract the release of an endogenous nitric oxide synthase inhibitor, improve survival, and decrease intraoperative hypertension after infrarenal aortic cross-clamp surgery. Hindlimb ischemia was generated by infrarenal aortic cross-clamping and tying of the left femoral artery for 5 hours in rats with bilateral femoral and sciatic nerves cut. Mean blood pressure significantly increased during the 5-hour ischemic period in ischemic rats (no drug treatment). Baroreceptor function was inhibited in ischemic rats assessed by intravenous dose response to phenylephrine and nitroprusside after 5 hours of ischemia, suggesting baroreceptor resetting. In ischemic rats infused with L-arginine the intraoperative hypertension was prevented during the 5-hour period, suggesting that this hypertension may be mediated by nitric oxide inhibition. The rates of survival and arrhythmias 2 hours after declamping were 50% in ischemic rats and 100% in ischemic rats treated with N omega-nitro-L-arginine (a nitric oxide synthase inhibitor) 10 minutes before declamping. In ischemic rats infused with L-arginine the survival rate was significantly increased to 100% and the arrhythmic rate was inhibited. We conclude that L-arginine prevents hypertension during cross-clamping and decreases the mortality rate and arrhythmias after declamping by maintaining nitric oxide synthesis. These results suggest that humoral factors released from the ischemic hindlimb may inhibit endogenous nitric oxide production, thus contributing to intraoperative hypertension, arrhythmias, and high mortality rate after aortic cross-clamp surgery.

Topics: Animals; Arginine; Hindlimb; Hypertension; Ischemia; Male; Nitric Oxide; Nitroarginine; Pressoreceptors; Rats; Rats, Sprague-Dawley

Hypertension is thought to alter many of the functions of the vascular endothelium. The present study examines whether shear stress-induced endothelium-dependent skeletal muscle arteriolar dilation is compromised in genetically hypertensive rats. Changes in the diameter of isolated, perfused arterioles (approximately 60 microns) from gracilis muscles of 12-week-old normotensive Wistar rats (NWR) and spontaneously hypertensive rats (SHR) were investigated. At a constant perfusion pressure (80 mm Hg), the active diameter of NWR and SHR arterioles was 57.1 +/- 2.0 and 50.9 +/- 3.5 microns, respectively (mean +/- SEM), while the passive diameter (in Ca(2+)-free solution) was 113.2 +/- 3.1 and 100.6 +/- 2.9 microns, respectively. Increases in wall shear stress (from 0 to 100 dyne/cm2) elicited by increases in perfusate flow (from 0 to 25 microL/min) resulted in marked increases in the diameter of NWR arterioles, but such increases produced substantially smaller dilations in SHR arterioles (43.0 versus 18.9 microns). The prostaglandin synthesis inhibitor indomethacin (10(-5) mol/L) significantly attenuated the shear stress-induced dilations in both strains of rats. In contrast, the nitric oxide synthase inhibitor N omega-nitro-L-arginine (10(-4) mol/L) significantly shifted the shear stress-diameter curve to the right in vessels from NWR (by 50 dyne/cm2) but not in those from SHR. Thus, in gracilis muscle arterioles of SHR, the reduced dilation to increases in shear stress seems to be due to the lack of nitric oxide synthesis and/or release in response to shear stress.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Animals; Arginine; Arterioles; Blood Pressure; Hypertension; Indomethacin; Male; Muscle, Skeletal; Nitric Oxide; Nitroarginine; Perfusion; Prostaglandin Antagonists; Rats; Rats, Inbred SHR; Rats, Wistar; Reference Values; Stress, Mechanical; Vasodilation

In anesthetized intact rats, cerebral blood flow is autoregulated until mean arterial blood pressure (MAP) exceeds 150 mmHg. At higher pressures cerebral blood flow breaks through autoregulation and rapidly increases. However, interruption of the arterial baroreceptor reflex eliminates breakthrough of autoregulation. Thus, breakthrough may reflect active rather than passive vasodilatation. We, therefore, sought to determine if breakthrough depends upon synthesis of the vasodilator nitric oxide. Thirty-eight anesthetized adult male Sprague-Dawley rats were studied. In all, MAP was raised by slow i.v. infusion of phenylephrine. In rats pretreated with the nitric oxide synthase inhibitor L-nitroarginine (L-NA; 22 mg/kg i.v.) or with a combination of L-NA plus D-arginine (D-Arg; 240 mg/kg i.v.), breakthrough did not occur even when MAP exceeded 185 mmHg (L-NA) and 165 mmHg (D-Arg). In contrast, breakthrough occurred in rats treated with L-NA plus L-arginine (L-Arg; 240 mg/kg i.v.) and in rats whose basal vascular tone had been increased by pretreatment with arginine vasopressin prior to infusion of phenylephrine. Removal of sympathetic innervation to cerebral vessels attenuated, but did not eliminate, effects of L-NA on breakthrough. Thus, vasodilatation seen with breakthrough of autoregulation depends upon release of nitric oxide or a nitric oxide donor.

Topics: Animals; Arginine; Arginine Vasopressin; Cerebrovascular Circulation; Homeostasis; Hypertension; Male; Nitric Oxide; Nitroarginine; Rats; Rats, Sprague-Dawley; Vasoconstriction

To investigate if the functional alterations observed in resistance arteries of spontaneously hypertensive rats (SHRs) were also present at the coronary level, in vitro experiments were performed in mesenteric resistance arteries (MRA) and in right (RIC) and left interventricular coronary (LIC) arteries taken from 15-25-week-old SHR and age-matched Wistar Kyoto rats WKYs. Using a passive extension protocol, internal diameters corresponding to 100 mmHg intraluminal pressure (D100) were determined and vessels were set up to a normalized internal diameter (0.9 D100). SHR mesenteric resistance arteries had a significantly smaller diameter compared to WKY arteries, whereas both types of SHR coronary arteries had a greater diameter compared to those of WKY rats. In arteries in the absence of contracting agonist, nitro-L-arginine (NOLA, 100 microM) induced a progressive rise in basal tone, which could be reversed by subsequent addition of L-arginine (100 microM) but not D-arginine (100 microM). When expressed as percent of maximal contractions induced by agonists (noradrenaline, NA [10 microM] in MRA; serotonin, 5-HT [10 microM], in RIC and LIC), these contractions were significantly stronger in WKY compared to SHR coronary and mesenteric resistance arteries. In NA-precontracted MRA and 5HT-precontracted coronary arteries in the presence of indomethacin (10 microM), the magnitude of acetylcholine-induced maximal relaxations (expressed as percent of maximal contractions induced by agonists) was greater in WKY compared to SHR arteries. After a 30-min incubation period, NOLA (100 microM) completely inhibited relaxations induced by acetylcholine (0.01-10 microM) in all types of precontracted arteries.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Acetylcholine; Animals; Arginine; Coronary Vessels; Endothelium, Vascular; Hypertension; Mesenteric Arteries; Muscle, Smooth, Vascular; Nitroarginine; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Vasoconstriction

Renal autoregulation curves are reset toward higher renal arterial pressure in spontaneously hypertensive rats (SHR) compared with those in Wistar-Kyoto rats (WKY). We previously demonstrated that myogenic afferent arteriolar constriction is shifted to higher renal arterial pressure. To investigate whether nitric oxide participates in the regulation of myogenic tone, we examined the effect of nitro-L-arginine on myogenic afferent arteriolar constriction in kidneys from SHR and WKY, using the isolated perfused hydronephrotic kidney. Elevating pressures from 40 to 80 mm Hg caused increases in afferent arteriolar diameter in WKY (from 18.2 +/- 0.4 to 19.0 +/- 0.3 micron) and SHR (from 17.3 +/- 0.6 to 18.4 +/- 0.6 micron). Further pressure elevation elicited constriction at 100 mm Hg in WKY (17.9 +/- 0.3 micron), but significant constriction was observed at 120 mm Hg in SHR (17.3 +/- 0.6 micron), indicating a resetting in myogenic responses to higher pressures. In WKY, after treatment with 10 mumol/L nitro-L-arginine, afferent arterioles exhibited pressure-dependent constriction, with a threshold pressure for constriction at 80 mm Hg. The addition of 100 mumol/L nitro-L-arginine had no further effect on myogenic responsiveness in WKY. In contrast, in SHR, nitro-L-arginine dose-dependently shifted the myogenic responses toward lower renal arterial pressure, with threshold pressures for constriction observed at 100 mm Hg (10 mumol/L) and 80 mm Hg (100 mumol/L).(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Animals; Arginine; Arterioles; Homeostasis; Hydronephrosis; Hypertension; Kidney; Male; Nitric Oxide; Nitroarginine; Nitroprusside; Perfusion; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Receptors, Vasopressin; Vasoconstriction

This study was designed to evaluate the effect of chronic treatment with cilazapril on vascular reactivity of aorta and mesenteric artery from Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR). Cilazapril (5 mg/kg), an angiotensin converting enzyme inhibitor, was injected intraperitoneally twice a day for 4 weeks. Results demonstrated that acetylcholine (ACh)-induced relaxation in aorta and mesenteric artery from SHR was significantly less than that from WKY, cilazapril-treated WKY, and SHR. The impairment of ACh-induced relaxation in SHR was significantly reversed after cilazapril treatment and there were no significant differences among WKY, cilazapril-treated WKY, and SHR. Meanwhile, both N omega-nitro-L-arginine (LNNA; 10(-4) mol/L) and methylene blue (MB; 10(-5) mol/L) completely blocked the vasodilator response to ACh in aorta but only partly inhibited in mesenteric artery from WKY, cilazapril-treated WKY, and SHR. These LNNA- and MB-resistant vasodilator responses to ACh in mesenteric artery were only slightly inhibited by TEA (10(-3) mol/L) but not by indomethacin (5 x 10(-6) mol/L). These findings suggest that there may be an unidentified endothelium-dependent relaxing factor(s) (EDRF), which exists in the endothelium and may participate in the modulation of blood pressure in SHR. Results further demonstrate that the antihypertensive effect of cilazapril may be partly mediated by the reversing function of endothelium to release EDRF and LNNA-resistant, unidentified relaxing factor(s).

Topics: Acetylcholine; Angiotensin-Converting Enzyme Inhibitors; Animals; Arginine; Blood Pressure; Cilazapril; Enzyme Inhibitors; Hypertension; Injections, Intraperitoneal; Mesenteric Arteries; Nitric Oxide; Nitroarginine; Random Allocation; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Vasodilation

We examined the effect of long-term nitric oxide (NO) synthase inhibition on vascular and renal endothelin-1 levels and evaluated the antihypertensive effect of endothelin ETA receptor antagonist FR139317 ((R)2(-)[(R)-2(-)[(S)-2(-)[[1-(hexahydro-1H-azepinyl)]- carbonyl]amino-4-methyl-pentanoyl]amino-3(-)[3-(1-methyl-1H- indolyl)]propionyl]amino-3-(2-pyridyl) proprionic acid] on rats in which NO synthase was blocked. Chronic NO blockade was produced by oral administration of the NO synthase inhibitor NG-nitro-L-arginine for 4 weeks, which produced sustained hypertension. At the end of this time, there were no significant changes in aortic and renal immunoreactive-endothelin levels between NG-nitro-L-arginine-treated hypertensive rats and normotensive control rats. Intravenous injection of FR139317 (10 mg/kg), which had a sufficient hypotensive effect on deoxycorticosterone acetate-salt hypertensive rats, to NG-nitro-L-arginine-treated hypertensive rats produced only a moderate hypotensive effect, to the same degree as seen in normotensive rats. The results indicate that long-term NO synthase inhibition did not affect vascular and renal endothelin-1 levels in these rats. It seems likely that endothelin-1 and ETA receptors do not contribute to the sustained hypertension induced by NO synthesis blockade.

Topics: Administration, Oral; Analysis of Variance; Animals; Arginine; Azepines; Blood Pressure; Desoxycorticosterone; Disease Models, Animal; Endothelin Receptor Antagonists; Endothelins; Enzyme Inhibitors; Hypertension; Indoles; Injections, Intravenous; Kidney; Male; Nitric Oxide Synthase; Nitroarginine; Rats; Rats, Sprague-Dawley; Receptor, Endothelin A

Decreased response to vasopressor agents characterizes pregnancy. Endothelium-derived relaxing factors and vasodilating prostaglandins play an important role in the vascular tone during pregnancy. Since inhibition of nitric oxide (NO) biosynthesis induced by NO2-arginine enriched diet produced hypertension we measured in vivo cardiovascular responses to PGF2 alpha, L-arginine (L-arg) and cicletanine (Cic, IPSEN, France) which enhances PGI2 production. From day 13 to day 20 of gestation 4 groups of female Wistar rats were fed NO2-arg (31 mg/kg/d), NO2-arg+Cic (10 mg/kg/d), Cic enriched or control diet (C). Mean arterial pressure (MAP) was measured via a carotid catheter in anesthetized rats. Injection of PGF2 alpha (50 micrograms/kg) in jugular vein significantly increased MAP in the NO2-arg group versus, NO2-arg+Cic, Cic and C group (+23.5 +/- 3.3 vs +15.7 +/- 2.2, +15.8 +/- 2.2 and +17 +/- 1.85 mmHg; p < 0.01). Injection of L-arg (100 mg/kg) or Cic (1 mg/kg) 5 min before PGF2 alpha produced no modification in MAP in C and Cic group. Likewise in NO2-arg group injection of L-arg or Cic produced a diminished pressor response to PGF2 alpha (+23.5 +/- 3.3 vs -17.5 +/- 1.7 mmHg; p < 0.05 and +15.2 +/- 2.4 mmHg; p < 0.01 respectively). In NO2-arg+Cic group, only injection of Cic induced a diminished pressor response to PGF2 alpha which is more important without L-arg (+15.7 +/- 2.2 vs +9.1 +/- 1.3 mmHg; p < 0.001) or with L-arg (+13.6 +/- 1.5 vs +9.1 +/- 1.3 mmHg; p < 0.01). Cicletanine also significantly diminished the proteinuria in the NO2-arg+Cic group versus NO2-arg group (13.9 +/- 4.36 vs 63.4 +/- 21.6 mmHg; p < 0.01). IN CONCLUSION, chronic NO synthesis inhibition enhanced blood pressure and pressor responses to PGF2 alpha during pregnancy in rats. Chronic administration of cicletanine in Wistar pregnant rats decreases the response to vasopressor agents like PGF2 alpha. Moreover acute and chronic administration of cicletanine blunted the pressor effect, which was lower than in normal gestation.

Topics: Animals; Antihypertensive Agents; Arginine; Blood Pressure; Dinoprost; Enzyme Inhibitors; Female; Hypertension; Nitric Oxide; Nitroarginine; Oxytocics; Pregnancy; Pregnancy Complications, Cardiovascular; Pregnancy, Animal; Prostaglandins F; Proteinuria; Pyridines; Rats; Rats, Wistar; Vasoconstriction

This study examined the activity of sodium nitroprusside (SNP) in the human fetal-placental circulation in vitro in pathological and experimental conditions in which vascular function may be impaired. SNP (13-3400 nM) caused a concentration-dependent reduction in fetal arterial perfusion pressure (FAP) in Krebs' perfused placental cotyledons, at basal tone and following pre-constriction with prostaglandin F2 alpha (PGF2 alpha). SNP-induced reduction in FAP in the PGF2 alpha pre-constricted fetal-placental circulation was enhanced approximately six-fold (5.85) in those placentae pre-treated with the nitric oxide (NO) synthase inhibitor N omega-nitro-L-arginine (100 microM). Reductions in FAP in the preconstricted fetal-placental vasculature caused by SNP were not altered by prior infusion of ouabain (100 nM) into the fetal circulation or during low oxygen perfusion (O2 tension < 50 mmHg). No differences were observed in the responses obtained to SNP in placentae obtained from women with normotensive pregnancies or those associated with (i) pregnancy-induced hypertension, (ii) intra-uterine growth retardation, or (iii) an elevated umbilical-artery Doppler-ultrasound systolic/diastolic ratio, in either preconstricted placentae or those at basal tone. These findings are consistent with an up-regulation of guanylate cyclase/cGMP-mediated vasodilatation in the fetal-placental vasculature following complete blockade of endogenous NO production.

Topics: Adolescent; Adult; Arginine; Blood Pressure; Dinoprost; Enzyme Inhibitors; Female; Fetal Growth Retardation; Fetus; Humans; Hypertension; In Vitro Techniques; Nitric Oxide Synthase; Nitroarginine; Nitroprusside; Ouabain; Placenta; Pre-Eclampsia; Pregnancy; Pregnancy Complications; Vasoconstriction; Vasodilation

1. Endothelium-dependent relaxation by alpha-adrenoceptor agonists was examined in the thoracic aorta from normotensive Wistar-Kyoto (WKY) rats and stroke-prone spontaneously hypertensive rats (SHRSP). 2. In ring preparations from both strains, noradrenaline-induced contraction was increased by L-nitro arginine (L-NNA), a NO synthesis inhibitor. 3. L-NNA increased the contraction induced by phenylephrine, an alpha1-adrenoceptor agonist. UK-14304 and clonidine, alpha2-adrenoceptor agonists, did not contract the preparations with intact endothelium. However, these agents contracted preparations when NO synthesis was inhibited. 4. In a precontracted preparation, clonidine and UK-14304 induced relaxations. The relaxations in SHRSP aorta were smaller than those in WKY aorta. 5. These results indicate that alpha-agonists release NO from endothelium in WKY and SHRSP aorta. The mechanism related to NO release by alpha2-adrenoceptor agonist is impaired in SHRSP aorta.

Topics: Adrenergic alpha-Agonists; Animals; Aorta, Thoracic; Cerebrovascular Disorders; Enzyme Inhibitors; Hypertension; In Vitro Techniques; Muscle Contraction; Muscle, Smooth, Vascular; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Norepinephrine; Rats; Rats, Inbred SHR; Rats, Inbred WKY

1. The experiments were carried out by an ordinary and a microsphere method in order to clarify the effects of three nitric oxide-synthase inhibitors and -donor on the circulating system between SHRSP and WKY. 2. Intravenous administration of each compound possessing the nitric acid-synthase inhibiting action markedly elevated the systolic blood pressure both in SHRSP and WKY, but more prominently in the former. 3. The hypotensive and tachycardic responses to glyceryl trinitrate were more enhanced after treatment with NG-nitro-L-arginine and NG-nitro-L-arginine methyl ester but not with NG-monomethyl-L-arginine compared with the non-treated one. 4. All peripheral organs except the brain decreased their regional blood flow after administration of NG-nitro-L-arginine, indicating a crucial involvement of nitric oxide in the peripheral circulation. 5. It was suggested that the nitric oxide system worked more sensitively and actively in SHRSP than in WKY in order to maintain the peripheral blood flow and systemic blood pressure.

Topics: Animals; Blood Pressure; Cerebrovascular Disorders; Enzyme Inhibitors; Heart Rate; Hemodynamics; Hypertension; Microspheres; NG-Nitroarginine Methyl Ester; Nitric Oxide Synthase; Nitroarginine; Nitroglycerin; omega-N-Methylarginine; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Regional Blood Flow; Vasodilator Agents

1. The effects of chronic NG-nitro-L-arginine (LNA) feeding on the endothelial function in isolated coronary arteries from stroke-prone spontaneously hypertensive rats (SHRSP) and normotensive Wistar-Kyoto (WKY) rats were studied. 2. A diet containing LNA (0.02%) was given to male SHRSP and WKY at 6 weeks of age and the coronary arteries were dissected on the 10th day of feeding. 3. In the SHRSP and WKY fed the LNA-free diet, acetylcholine (ACh) relaxed the precontracted ring segments of the coronary artery with intact endothelium in a dose-dependent manner. The reactivity was stronger in the WKY than in the SHRSP. However, the ACh-induced relaxation after the LNA-feeding was significantly stronger in the coronary arteries from the WKY than in those from the SHRSP. 4. The relaxation induced by the calcitonin gene-related peptide (CGRP) was endothelium-dependent and endothelium-independent. The degree of the response in the rats fed the LNA-containing diet was not significantly different from that in the rats fed the LNA-free diet. 5. The vasodilator response induced by sodium nitroprusside (SNP) was dose-dependent and similar in the rats fed the LNA containing diet and the LNA-free diet. 6. These findings indicate that chronic LNA feeding markedly impaired the endothelial nitric oxide formation in the coronary artery from young SHRSP.

Topics: Animals; Blood Pressure; Body Weight; Coronary Vessels; Diet; Endothelium, Vascular; Enzyme Inhibitors; Hypertension; Male; Muscle Relaxation; Muscle, Smooth, Vascular; Nitric Oxide Synthase; Nitroarginine; Rats; Rats, Inbred SHR; Rats, Inbred WKY

The present study evaluates the response to the L-type voltage gated calcium channel agonist Bay K 8644 in two forms of experimental hypertension (mineralocorticoid- and hypertension induced by the nitric oxide synthase inhibitor N omega-nitro-L-arginine (N-Nitro arginine)) and under conditions of acute stretch. These studies test the hypothesis that increased L-type calcium channel activity in vasculature is a hallmark or general characteristic of hypertension. Male Sprague-Dawley rats were made hypertensive by subcutaneous implantation of deoxycorticosterone acetate (200 mg/kg DOCA) and given normal or high salt water (1% NaCl + 0.2% KCl); other rats were made hypertensive by ingestion of N-Nitro arginine (2% in water). Systolic blood pressures (SBP) were taken by the standard tail cuff method. Following development of hypertension, rats were anesthetized, and aortae or mesenteric arteries were isolated for measurement of isometric contractile force. Cumulative concentration response curves to Bay K 8644 (10(-10) to 10(-6) M), KCl (6 to 100 mM), or phenylephrine (10(-10)-3 x 10(-7) M) were evaluated. Isolated mesenteric arteries from rats given both DOCA and salt were most sensitive to Bay K 8644 (SBP = 191 +/- 6 mmHg, -log EC50 = 7.78 +/- 0.13), followed by rats receiving high salt alone (SBP = 118 +/- 6 mmHg, -log EC50 = 7.30 +/- 0.17), DOCA alone (SBP = 152 +/- 2 mmHg, -log EC50 = 7.25 +/- 0.15), and finally normal sham rats (SBP = 111 +/- 5 mm Hg, -log EC50 > or = 6.80 +/- 0.10). These data indicate that both DOCA and salt intake can independently influence responsiveness to Bay K 8644.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: 3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; Administration, Oral; Amino Acid Oxidoreductases; Animals; Aorta, Thoracic; Arginine; Blood Pressure; Calcium Channels; Desoxycorticosterone; Dose-Response Relationship, Drug; Drug Implants; Hypertension; Male; Mesenteric Artery, Superior; Muscle, Smooth, Vascular; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Phenylephrine; Potassium Chloride; Rats; Rats, Sprague-Dawley; Sodium Chloride, Dietary; Stress, Mechanical; Vasoconstriction

1. The role of the endothelium in cerebrovascular responses to 5-hydroxytryptamine (5-HT) was investigated in spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY) in vitro. 2. Cumulative addition of 5-HT caused concentration-dependent contractions in ring preparations of SHR basilar arteries; the contractile response was smaller in WKY basilar arteries. 3. Removal of the endothelium enhanced markedly the contractile responses to 5-HT in WKY arteries but had only a slight effect in SHR arteries. The responsiveness to 5-HT in WKY arteries after removal of endothelium was comparable to that in SHR arteries. 4. The endothelium-dependent relaxation induced by acetylcholine in WKY basilar arteries was almost abolished by treatment with 10 microM methylene blue or 10 microM NG-nitro-L-arginine (L-NOARG). However, the response to 5-HT was not affected by treatment with methylene blue, L-NOARG or indomethacin. 5. Application of 10-20 mM K+ or 3.2 mM tetraethylammonium (TEA) did not change significantly, or only increased slightly, the resting tension, but markedly enhanced the contractile response to 5-HT in WKY arteries with endothelium. In contrast, the submaximal response to 5-HT in SHR arteries with endothelium was significantly enhanced by 0.3 mM TEA. 6. In the presence of 1 mM TEA, the application of 10 microM L-NOARG further enhanced the responses of 5-HT in WKY arteries with endothelium. In SHR arteries with endothelium, 10 microM L-NOARG per se enhanced slightly but significantly the responses to 5-HT. 7. These results indicate that 5-HT-induced contraction in basilar arteries is substantially attenuated by an endothelium-dependent mechanism in WKY, but to a much lesser extent in SHR. The major relaxing factor released by 5-HT from endothelium in WKY is distinct from NO and may exert its effect by activating K+ channels.

Topics: Animals; Arginine; Basilar Artery; Cerebrovascular Circulation; Endothelium, Vascular; Hypertension; Male; Methylene Blue; Muscle Contraction; Muscle Relaxation; Muscle, Smooth, Vascular; Nitric Oxide; Nitroarginine; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Serotonin

Clonidine, an alpha 2-agonist, caused a concentration-dependent vasodilation of the mesenteric arterial beds in both normotensive and hypertensive rats. The clonidine-induced vasodilation was inhibited by NG-nitro-L-arginine, and the inhibition was reversed by L-arginine. The concentration-dependent vasodilation was not significantly different between normotensive and hypertensive rats. These results suggest that clonidine has an endothelium-dependent vasorelaxant action in the resistance artery such as rat mesenteric arterial bed, and the endothelium-dependent vasodilator effects of clonidine in the mesentery may be involved in the depressor effect of the drug.

Topics: Animals; Arginine; Blood Pressure; Clonidine; Dose-Response Relationship, Drug; Endothelium, Vascular; Hypertension; Male; Mesenteric Arteries; Muscle, Smooth, Vascular; Nitroarginine; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Vasodilation

We tested the hypothesis that impairment of flow-dependent dilator mechanisms of skeletal muscle arterioles is one of the underlying reasons for the increased peripheral resistance in hypertension. Isolated, cannulated arterioles (approximately 55 microns) of gracilis muscle of 12-week-old spontaneously hypertensive (SH) and normotensive Wistar (NW) rats were investigated. At a constant perfusion pressure (80 mm Hg), the active diameters of NW and SH arterioles were 57.7 +/- 1.9 and 51.5 +/- 3.2 microns, whereas their passive diameters (Ca(2+)-free solution) were 113.6 +/- 2.9 and 101.7 +/- 2.9 microns, respectively. Flow-induced dilation was elicited by increases in flow of the perfusion solution from 0 to 25 microL/min in 5-microL/min steps. This response was significantly less in arterioles of SH compared with NW rats. For example, at 25-microL/min flow, the diameter of arterioles of SH rats was approximately 56% less (P < .05) than those of NW rats. Indomethacin, an inhibitor of prostaglandin synthesis, significantly attenuated the flow-diameter curve in both strains of rats. In contrast, N omega-nitro-L-arginine, a nitric oxide synthase inhibitor, significantly shifted the flow-diameter curve to the right in NW rats, but it did not affect the flow-diameter curve in SH rats. Thus, the present findings demonstrate that in gracilis muscle arterioles of normotensive rats in response to increases in flow (shear stress), prostaglandins and nitric oxide are co-released, resulting in a dilation. In early hypertension, however, there is a reduced arteriolar dilation to increases in flow that is due to the impairment of the nitric oxide-mediated portion of the flow-dependent arteriolar dilation.

Topics: Animals; Arginine; Arterioles; Hypertension; In Vitro Techniques; Indomethacin; Male; Muscles; Nitric Oxide; Nitroarginine; Prostaglandins; Rats; Rats, Inbred SHR; Rats, Wistar; Regional Blood Flow; Vasodilation

Deendothelialized rings of rabbit aorta relax after exposure to UV light because of release of a relaxing factor that is similar if not identical to nitric oxide. We tested the hypothesis that production of the photo-induced relaxing factor is impaired in a rat model of genetic hypertension. Thoracic aortas were removed from adult Wistar-Kyoto rats and stroke-prone spontaneously hypertensive rats. The vessels were cut into rings, denuded of endothelium, and placed in a muscle bath for isometric force measurement. Rings were contracted with phenylephrine, and relaxation was measured after exposure to UV light. Aortic rings from stroke-prone spontaneously hypertensive rats relaxed to a greater extent after exposure to UV light than did rings from Wistar-Kyoto rats. An inhibitor of nitric oxide synthase (N omega-nitro-L-arginine) greatly potentiated the relaxation responses to light in both strains, and these enhanced relaxations were attenuated by tetraethylammonium chloride, potassium chloride, ouabain, or inhibitors of guanylate cyclase. These results suggest that UV irradiation induces relaxation in aortic smooth muscle that is greater in hypertensive than normotensive rats and is greatly enhanced after addition of inhibitors of nitric oxide production. Thus, the unidentified photo-induced relaxing factor is not solely nitric oxide but may also represent either a hyperpolarizing factor, because depolarization blocks the responses entirely, or possibly smooth muscle guanylate cyclase that might itself be photoactivable.

Topics: Animals; Aorta, Thoracic; Arginine; Female; Hypertension; In Vitro Techniques; Male; Muscle Proteins; Nitric Oxide; Nitroarginine; Phenylephrine; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Ultraviolet Rays; Vasodilation

Topics: Amino Acid Oxidoreductases; Angiotensin II; Animals; Arginine; Electric Stimulation; Female; Hypertension; In Vitro Techniques; Mesenteric Artery, Superior; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Norepinephrine; Pregnancy; Pregnancy Complications, Cardiovascular; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Vasodilation

Topics: Amino Acid Oxidoreductases; Animals; Arginine; Blood Pressure; Bradykinin; Hypertension; Hypertrophy, Left Ventricular; Male; Nitric Oxide Synthase; Nitroarginine; Organ Size; Rats; Rats, Sprague-Dawley

This study aimed to determine the mechanism of hypertension associated with nitric oxide synthase inhibition. Intravenous injections of NG-nitro-L-arginine, a nitric oxide synthase inhibitor, produced a sustained increase in systemic blood pressure and a decrease in heart rate in anesthetized dogs, whereas NG-nitro-D-arginine had no effect. L-Arginine reversed the pressor response. NG-Nitro-L-arginine-induced hypertension was markedly attenuated or abolished by treatment with hexamethonium; this inhibition was still observed when the blood pressure fall caused by the ganglionic blocking agent was compensated by continuous infusion of angiotensin II. In dogs treated with phentolamine in a dose sufficient to lower blood pressure to the level similar to that elicited by hexamethonium and to suppress the pressor response to norepinephrine, the hypertensive effect of NG-nitro-L-arginine was not attenuated. We conclude that hypertension caused by the nitric oxide synthase inhibitor is associated with an elimination of nitroxidergic neural function rather than an impairment of the basal release of nitric oxide from the endothelium.

Topics: Amino Acid Oxidoreductases; Animals; Arginine; Blood Pressure; Dogs; Female; Heart Rate; Hexamethonium; Hexamethonium Compounds; Hypertension; Male; Nitric Oxide Synthase; Nitroarginine; Phentolamine

To determine whether inhibition of generation of endothelium-derived relaxing factor or nitric oxide (NO) resulted in elevated blood pressure and its effect on resistance arteries, rats were offered NG-nitro-L-arginine methyl ester (L-NAME), a competitive inhibitor of NO synthase, in their drinking water. Blood pressure (BP) rose slightly from 100 +/- 2 mmHg in controls to 130 +/- 5 mmHg with 25 mg/Kg L-NAME per day and to 173 +/- 9 mmHg with 100 mg/Kg per day for 2 1/2 to 4 weeks. Rats were studied after 1-2 weeks of hypertension (BP > 150 mmHg). The concentration of cyclic guanosine monophosphate, the intracellular second messenger of NO, was significantly depressed in aorta and in the mesenteric vascular bed in L-NAME-treated rats. Mesenteric resistance arteries studied on a wire-myograph exhibited similar external and lumen diameters, whereas media width and media/lumen ratio were greater (p < 0.01). Cross-sectional area of the media was similar. Active wall tension in response to norepinephrine tended to be greater in blood vessels from L-NAME-treated rats, while responses to vasopressin and endothelin-1 were unaltered. Sensitivity to norepinephrine was significantly enhanced in L-NAME-treated rats (p < 0.001), while that to endothelin-1 and arginine8 vasopressin was similar. In conclusion, administration of an NO synthase inhibitor produces hypertension, with exaggerated media/lumen ratio in resistance arteries and enhancement of response to norepinephrine, which together with decreased NO generation may contribute to elevation of blood pressure.

Topics: Amino Acid Oxidoreductases; Animals; Arginine; Arteries; Blood Pressure; Hypertension; Nitric Oxide Synthase; Nitroarginine; Rats; Rats, Sprague-Dawley; Vascular Resistance

Blockade of the renin-angiotensin system was studied in male Sprague-Dawley rats during long-term inhibition of nitric oxide synthase. Nitro-L-arginine-methyl ester (L-NAME) was placed in the drinking water for 4 weeks (approximately 100 mg/kg per day). Separate groups of rats were coadministered the angiotensin II antagonist A-81988 in the drinking water ranging from approximately 0.001 to 1 mg/kg per day. Control groups received only tap water or A-81988 alone. Each week, rats were placed in metabolic cages, and tail-cuff blood pressures and blood samples were taken. L-NAME produced a sustained elevation in tail-cuff pressure that was completely prevented by A-81988. No changes in creatinine clearance, sodium excretion, plasma creatinine concentration, or blood urea nitrogen were observed. Food and water intakes were identical in all groups. Water excretion was significantly increased in L-NAME-treated animals regardless of additional inhibitor treatment, suggesting a possible role for nitric oxide synthase in the control of water excretion; this effect was independent of blood pressure. Although less potent than A-81988, the angiotensin II antagonist losartan and the angiotensin converting enzyme inhibitor enalapril also blocked L-NAME-induced hypertension. In a separate series of experiments, rats were not given A-81988 until 2 weeks after hypertension had fully developed in L-NAME-treated rats. Within 1 week of treatment with the angiotensin II antagonist, tail-cuff pressure returned to normal. We conclude from these studies that long-term inhibition of endogenous nitric oxide production produces an angiotensin II-dependent form of hypertension.

Topics: Amino Acid Oxidoreductases; Angiotensin II; Animals; Arginine; Diuresis; Dose-Response Relationship, Drug; Hypertension; Male; Nicotinic Acids; Nitric Oxide Synthase; Nitroarginine; Proteinuria; Pyridines; Rats; Rats, Sprague-Dawley; Renin; Tetrazoles; Time Factors

We have investigated the effects of L-NG-nitro arginine (L-NOARG), glibenclamide, ouabain, tetraethylammonium and 4-aminopyridine on the methacholine-induced endothelium-dependent vasodilation in perfused resistance arteries from spontaneously hypertensive rats (SHR) and Wistar Kyoto rats (WKY). Since the concentration-response curves of MCh were similar in both types of preparations there does not seem to exist an endothelial dysfunction in mesenteric arteries of SHR. L-NOARG only partially inhibited the maximal methacholine-induced response in preparations taken from SHR and WKY rats. Ouabain decreased the maximal effect of methacholine without altering the potency (pD2). Preparations from SHR were more susceptible to ouabain. 4-aminopyridine and tetraethylammonium decreased the pD2 for methacholine without reducing the maximal effect (Emax). The WKY rat preparations were more affected by these compounds. An important role of ATP-sensitive potassium channels may be ruled out since glibenclamide was without effect on the methacholine-induced vasodilation. It is concluded that endothelium-derived relaxing factor is only partially responsible for the endothelium-dependent vasodilation. Indirect arguments point toward a role of endothelium-derived hyperpolarizing factor, since ouabain, tetraethylammonium and 4-aminopyridine inhibited the methacholine-induced response. Although hypertension related differences for these compounds were observed high blood pressure does not seem to alter the functional response to muscarinic stimulation.

Topics: 4-Aminopyridine; Animals; Arginine; Biological Factors; Endothelium, Vascular; Hypertension; In Vitro Techniques; Male; Mesenteric Arteries; Methacholine Chloride; Nitric Oxide; Nitroarginine; Perfusion; Potassium Channels; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Tetraethylammonium; Tetraethylammonium Compounds; Vasodilation

This study examined the contribution of endothelium-derived relaxing factor (EDRF) to the susceptibility of uninephrectomized rats to deoxycorticosterone acetate (DOCA)-salt hypertension. N omega-nitro-L-arginine, a probe for EDRF, produced smaller increases (P < 0.001) in mean arterial pressures in anesthetized hypertensive DOCA-salt rats than in sham rats. Acute L-arginine administration (300 mg/kg body wt i.v.) failed to reduce pressure in anesthetized DOCA-salt rats. Chronic oral and intraperitoneal L-arginine did not lower pressure in conscious DOCA-salt rats with established hypertension, nor did it prevent hypertension when begun in prehypertensive DOCA-salt rats. Preconstricted aortic rings from DOCA-salt rats had attenuated relaxation to acetylcholine compared with sham rats. Rings L-arginine-treated DOCA-salt rats had responses similar to DOCA-salt rats. Relaxation to nitroprusside was not different between any rat group. Thus EDRF is attenuated in DOCA-salt hypertension. However, unlike several other hypertensive models, the blunted EDRF response cannot be overcome by provision of L-arginine. These data suggest synthesis or release of EDRF may be noncompetitively inhibited in DOCA-salt hypertension.

Topics: Acetylcholine; Animals; Aorta; Arginine; Desoxycorticosterone; Hypertension; In Vitro Techniques; Injections, Intravenous; Male; Nitric Oxide; Nitroarginine; Rats; Rats, Sprague-Dawley; Sodium Chloride; Time Factors; Vasodilation

1. To examine the mechanisms which may account for pregnancy-induced vasodilatation in spontaneously hypertensive rats (SHR), we have investigated the changes in vascular reactivity and the effects of endothelial nitric oxide (NO) inhibition in the in situ blood-perfused, mesenteric resistance vessels of 18-20 day pregnant SHR. The effects of NG-nitro-L-arginine (L-NOARG) were compared in pregnant and nonpregnant SHR and gestation matched normotensive Wistar-Kyoto (WKY) rats. 2. Intra-arterial mean blood pressures (MBP) were similar in pregnant and nonpregnant SHR. Basal perfusion pressures (BPP) were decreased in pregnant compared with nonpregnant SHR. Pregnant WKY had lower MBP and BPP than either pregnant or nonpregnant SHR. 3. Vasoconstrictor responses to electrical stimulation (ES) and intra-arterial noradrenaline (NA) were decreased in pregnant compared with nonpregnant SHR. These responses were still greater in pregnant SHR when compared with pregnant WKY. Vascular reactivity to angiotensin II (AII) in pregnant SHR was reduced to a similar level to that in pregnant WKY. 4. L-NOARG (5 mg kg-1, i.v.), an inhibitor of nitric oxide synthase, increased MBP and BPP in all groups. After L-NOARG, BPP were equalized between pregnant and nonpregnant SHR. Pregnant WKY still showed lower MBP and BPP than SHR groups. 5. L-NOARG potentiated vascular responses to ES, NA and AII in all groups. The blunted vascular responses to NA and ES were normalized and the reactivity to AII was only partially reversed in pregnant SHR compared with nonpregnant SHR. Pregnant WKY still had much lower vascular responses to ES and NA than either pregnant or nonpregnant SHR. L-NOARG enhanced vascular responses to All to a greater extent in pregnant SHR than in pregnant WKY.6. These results demonstrate that blunted responses to NA and ES were NO-dependent, while diminished reactivity to AII was only partially dependent on NO in the in situ blood perfused mesenteric resistance vessels of pregnant SHR.7. The present results in pregnant SHR differ from our previous finding with pregnant normotensive WKY, in which blunted responses to NA, but not to ES, were equalized by L-NOARG. Pregnancy induced vasodilatation in hypertensive rats appears to be more dependent on endothelial NO than in normotensive WKY. A defect of the endothelial NO generating pathway which promotes vasodilatation in pregnancy may contribute to the predisposition of women with essential hypertension to develop pre-ecla

Topics: Animals; Arginine; Blood Pressure; Female; Hypertension; Nitric Oxide; Nitroarginine; Perfusion; Pregnancy; Pregnancy Complications, Cardiovascular; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Splanchnic Circulation; Vascular Resistance; Vasoconstriction; Vasodilation

To test whether endothelium-derived relaxing factor (EDRF) plays a role in regulating the hypertensive pulmonary vascular bed, we compared effects of the inhibitor of EDRF production, N omega-nitro-L-arginine (L-NNA), on resting vascular tone in lungs and conduit pulmonary arteries isolated from control and chronically hypoxic rats. In contrast to no effect on normoxic vascular tone in salt solution-perfused normotensive lungs, 100 microM L-NNA caused a marked, L-arginine-sensitive, precapillary vasoconstriction in unstimulated hypertensive lungs. Bioassay of hypertensive lung perfusate did not detect a circulating vasoconstrictor, and L-NNA vasoconstriction was not inhibited by blockers of cyclooxygenase, 5-lipoxygenase, platelet-activating factor receptors, alpha-adrenoceptors, and serotonin 5-HT2 receptors or by scavengers of superoxide anion and H2O2. Inhibitors of endothelin-1 (ET-1) production and vasoconstriction tended to blunt the response, but accumulation of perfusate ET-1 was not increased in hypertensive lungs. L-NNA vasoconstriction was blocked by Ca(2+)-free plus ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid perfusion but not by nifedipine. Quiescent, endothelium-intact hypertensive but not normotensive conduit pulmonary artery rings were markedly constricted by 200 microM L-NNA. The onset but not the peak of the response was blunted by meclofenamate. The response was reduced slightly by the ETA receptor antagonist, BQ 123. L-NNA had little effect on denuded hypertensive arteries, and treatment with dilators showed they had constricted spontaneously. Both the L-NNA and the spontaneous constrictions were readily inhibited by nifedipine. These results indicate that in rat hypertensive pulmonary arteries, the basal release of EDRF suppresses vasoconstrictor mechanisms which are not expressed in normotensive arteries.

Topics: Altitude; Animals; Arginine; Bradykinin; Hypertension; Lung; Male; Nitric Oxide; Nitroarginine; Pulmonary Artery; Pulmonary Circulation; Rats; Rats, Sprague-Dawley; Time Factors; Vasoconstriction

The purpose of this study was to determine whether cross-tolerance develops between nitroglycerin and endothelium-derived relaxing factor (EDRF)-mediated vasoactive agents in vivo. Spontaneously hypertensive rats (SHR) were made tolerant by pretreatment with high doses of nitroglycerin (100 mg/kg s.c., 3 times/day, for 3 consecutive days). The hypotensive effect of challenge doses of nitroglycerin (1, 10, 300, 100 micrograms/kg i.v.) was completely abolished in nitroglycerin-pretreated SHR. To evaluate cross-tolerance, the effects of the following EDRF-dependent vasoactive agents on blood pressure were determined in groups of nitroglycerin-pretreated and vehicle-pretreated SHR: acetylcholine, bradykinin and L-arginine. In addition, the hypotensive effects of zaprinast (M & B 22,928), a cyclic guanosine monophosphate (cGMP) phosphodiesterase inhibitor, and the hypertensive effects of the nitric oxide-synthase inhibitor N omega-nitro-L-arginine were also evaluated. In all cases, there was no difference in the effects of these agents on blood pressure when compared in nitroglycerin-pretreated (tolerant) and vehicle-pretreated (non-tolerant) SHR. The use of a variety of agents which modulate EDRF release or its effects by several different mechanisms suggests that cross-tolerance does not occur between nitroglycerin and EDRF in vivo.

Topics: 3',5'-Cyclic-GMP Phosphodiesterases; Acetylcholine; Animals; Arginine; Blood Pressure; Bradykinin; Drug Tolerance; Hypertension; Male; Nitric Oxide; Nitroarginine; Nitroglycerin; Purinones; Rats; Rats, Inbred SHR; Vasodilator Agents

Vascular relaxations are impaired in adult spontaneously hypertensive rats (SHRs) because of increased production of an endothelium-derived, cyclooxygenase-dependent contractile factor or factors. To test the hypothesis that alterations in endothelial function precede and contribute to the development of overt hypertension in SHRs, we compared in myographs endothelium-mediated relaxations of mesenteric resistance arteries from 4-week-old SHRs and Wistar-Kyoto (WKY) rats. Acetylcholine (10(-9) to 10(-4) M) induced comparable relaxations in SHR and WKY arteries precontracted (ED50) with norepinephrine. In arteries obtained from SHRs but not from WKY rats, relaxations were replaced by contractile responses with higher concentrations of acetylcholine (10(-6) to 10(-5) M). The contractile responses were endothelium dependent, were augmented by nitro L-arginine (10(-4) M), and were prevented by pretreatment with indomethacin (10(-5) M) or 3-amino-1,2,4-triazole (10(-3) M), an inhibitor of superoxide anion production via the cyclooxygenase pathway. Inhibition of thromboxane synthetase (CGS-13080, 5 x 10(-5) M) and antagonism of prostaglandin H2/thromboxane A2 receptors (SQ-29,548, 5 x 10(-5) M) failed to block the contractile response to acetylcholine in SHR arteries. Acetylcholine-mediated relaxations were significantly impaired in mesenteric arteries from 16-week-old SHRs but not from WKY rats. Endothelium-independent relaxations produced by sodium nitroprusside and contractile responses to norepinephrine and endothelin were comparable in arteries from SHRs and WKY rats of all ages. In summary, endothelium-dependent relaxations of mesenteric arteries from "prehypertensive" SHR rats were impaired by the production of a contractile factor (or factors) that appears to be superoxide anions.

Topics: Age Factors; Animals; Arginine; Endothelins; Endothelium, Vascular; Hydroxides; Hydroxyl Radical; Hypertension; In Vitro Techniques; Indomethacin; Male; Nitroarginine; Prostaglandin-Endoperoxide Synthases; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Vascular Resistance; Vasoconstriction; Vasodilation

Although the etiology of hypertension-related organ damage remains poorly understood, it has recently been proposed that activated and adherent leukocytes may contribute to the pathogenesis of progressive organ injury in hypertension. The objective of this study was to determine whether the adherence and emigration of leukocytes in microvessels differ between spontaneously hypertensive and normotensive rats. Leukocyte adherence, rolling, and emigration as well as vessel diameter and erythrocyte velocity were monitored in mesenteric venules of age-matched normotensive and hypertensive rats. Measurements were obtained under baseline conditions and during superfusion of the mesentery with either platelet activating factor, leukotriene B4, or NG-nitro-L-arginine-methyl ester, an inhibitor of nitric oxide synthesis. Tissue-associated myeloperoxidase activity, an index of the total tissue granulocyte population, was measured in various tissues of normotensive and hypertensive rats. Systemic arterial pressure and the circulating polymorphonuclear leukocyte count were elevated in hypertensive relative to normotensive rats. The number of adherent and emigrated leukocytes under baseline conditions did not differ between normotensive and hypertensive rats. Although the nitric oxide synthase inhibitor caused a similar rise in leukocyte adherence and emigration in both rat strains, the adhesive interactions elicited by either platelet activating factor or leukotriene B4 were significantly blunted in hypertensive relative to normotensive rats. Flow cytometric analysis of whole-blood samples revealed a lower surface expression of CD11b/CD18 on leukocytes from hypertensive rats under stimulated conditions. Myeloperoxidase activity in mesentery and small and large intestine was low, whereas lung, spleen, and stomach values were high in hypertensive compared with normotensive rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Animals; Arginine; Cell Adhesion; Endothelium, Vascular; Hypertension; Leukocyte Count; Leukocytes; Leukotriene B4; Male; Nitroarginine; Platelet Activating Factor; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Reference Values; Splanchnic Circulation; Stress, Mechanical

1. The haemodynamic and metabolic effects of oral intake of approximately 30 mg/kg per day N-nitro-L-arginine (NOLA) were examined in sham and adrenocorticotrophin (ACTH, 0.5 mg/kg per day) treated conscious Sprague-Dawley rats (n = 33). 2. NOLA administration produced an increase in systolic blood pressure of 24 +/- 6 mmHg (P < 0.001), but did not alter food or water intake, urine volume or electrolyte excretion in rats not treated with ACTH. 3. Compared with sham injection, ACTH-treated rats demonstrated an increase in systolic blood pressure (water + sham, 3 +/- 1 mmHg; water + ACTH, 16 +/- 3 mmHg; P < 0.001), loss of bodyweight, and increases in water intake and urine volume. 4. The magnitude of the blood pressure rise in ACTH-treated rats was greater in those receiving NOLA than in those drinking water only (water + ACTH, 16 +/- 3 mmHg; NOLA + ACTH, 37 +/- 3 mmHg; P < 0.05). Metabolic changes were similar. 5. Inhibition of nitric oxide is unlikely to be a major determinant of ACTH-induced hypertension in the rat, since NOLA increased blood pressure whether or not ACTH was administered, indicating an additive effect of ACTH and NOLA administration.

Topics: Adrenocorticotropic Hormone; Animals; Arginine; Drug Interactions; Hypertension; Male; Nitric Oxide; Nitroarginine; Rats; Rats, Sprague-Dawley; Water-Electrolyte Balance

The effect of a calcium antagonist, manidipine, on blood pressure and proteinuria induced by the inhibition of endothelial-derived relaxation factor (EDRF) formation was examined. Manidipine attenuated the increase in blood pressure and prevented proteinuria caused by renal damage associated with the inhibition of EDRF formation in stroke-prone spontaneously hypertensive rat (SHRSP) and Wistar Kyoto (WKY) rats.

Topics: Animals; Arginine; Blood Pressure; Calcium Channel Blockers; Cerebrovascular Disorders; Dihydropyridines; Hypertension; Male; Nitric Oxide; Nitroarginine; Nitrobenzenes; Piperazines; Proteinuria; Rats; Rats, Inbred SHR; Rats, Inbred WKY

1. Prolonged oral administration of NG-nitro-L-arginine (L-NNA) for a period of 5 weeks in 8 week old male normotensive Wistar-Kyoto (WKY) rats (n = 10), induced hypertension in all animals. Hypertension was characterized by a sharp initial increase in both systolic blood pressure (SBP) and mean blood pressure (MBP) until the third day (from 126 +/- 3 mmHg to 160 +/- 6 mmHg and from 95 +/- 3 mmHg to 133 +/- 6 mmHg, respectively). This was followed by a gradual and steady increase until the fourth week (163 +/- 4, 171 +/- 3 and 189 +/- 8 mmHg for SBP in weeks 1, 2 and 4, respectively; and 135 +/- 4, 143 +/- 3 and 157 +/- 5 mmHg for MBP in weeks 1, 2 and 4, respectively). 2. Intravenously L-arginine.HCl (500 mg/kg) administered on the last day of the 5th week abolished the effect of dietary L-NNA on the arterial blood pressure. 3. Dietary L-NNA-induced hypertension in WKY rats is easily obtainable and free of any surgical operation, and can be utilized as a new experimental model to further understand the importance of endothelium-dependent relaxing factor/nitric oxide in blood pressure regulation and to clarify the pathological significance in intact animals where endothelium-dependent relaxing factor/nitric oxide is functionally involved.

Topics: Animals; Arginine; Blood Pressure; Diet; Heart Rate; Hypertension; Male; Nitric Oxide; Nitroarginine; Rats; Rats, Inbred WKY

We investigated the role of nitric oxide (NO)-dependent and NO-independent mechanisms in mediation of renal vasodilatory responses to bradykinin in spontaneously hypertensive rats (SHR), rats with angiotensin II-induced hypertension (200 ng/min i.p. for 6 days) and the corresponding normotensive control Wistar-Kyoto (WKY) rats and sham-infused rats. To this end, we contrasted the effects of arterial injections of bradykinin and other vasodilators, acetylcholine and sodium nitroprusside, on perfusion pressure and output of cyclic GMP in isolated kidneys perfused with Krebs bicarbonate buffer containing phenylephrine, both with and without N omega-nitro-L-arginine (L-NOARG) (50 microM), an inhibitor of NO synthetase. In kidneys perfused without L-NOARG, all agonists increased the output of cyclic GMP and reduced perfusion pressure, indicative of vasodilation. In kidneys perfused with L-NOARG, vasodilatory responses to bradykinin and acetylcholine were attenuated, and associated effects on output of cyclic GMP were abolished, suggesting dependency on NO synthesis. Irrespective of whether kidneys were perfused with or without L-NOARG, kidneys of SHR were more responsive than kidneys of WKY rats with regard to bradykinin-induced vasodilation. In contrast, vasodilatory responsiveness to bradykinin was nearly equal in perfused kidneys of rats with angiotensin II-induced hypertension and in normotensive controls. Also, vasodilatory responsiveness to acetylcholine and sodium nitroprusside was similar in kidneys of normotensive and hypertensive rats. These data suggest that the renal vasculature of SHR is uniquely and selectively hyperresponsive to bradykinin, with regard to both the NO-dependent and NO-independent vasodilatory actions.

Topics: Acetylcholine; Animals; Arginine; Bradykinin; Cyclic GMP; Hypertension; Kidney; Nitric Oxide; Nitroarginine; Nitroprusside; Perfusion; Rats; Rats, Inbred SHR; Rats, Inbred Strains; Rats, Inbred WKY; Vasodilation

Topics: Animals; Arginine; Blood Pressure; Hypertension; Male; Nitric Oxide; Nitroarginine; Rats; Rats, Inbred SHR; Rats, Inbred Strains; Rats, Inbred WKY

1. NG-nitro-L-arginine (NO2Arg) is a guanidine nitro arginine derivative and an inhibitor of endothelium-dependent vascular relaxation. Significant rise of the systolic blood pressure was observed after 1 week administration of NO2Arg in food (0.023% in weight, about 2.8 mg of NO2Arg/rat per day) in female rats of stroke-prone spontaneously hypertensive rats (SHRSP) and normotensive Wistar-Kyoto rats (WKY). The rises were not different between SHRSP (21 mmHg) and WKY (23 mmHg). 2. In ring preparations of the thoracic aorta of NO2Arg-administered rats of both strains, relaxation by acetylcholine decreased markedly compared with those of the control rats (to 43-44%). On the contrary, glyceryltrinitrate-induced relaxation was slightly but significantly increased in the aorta of WKY after NO2Arg administration and the same tendency was observed in SHRSP. 3. The rise of blood pressure and the decrease of acetylcholine-induced relaxation suggested that NO2Arg inhibited the endothelium-dependent relaxation not only in WKY but also in SHRSP. The relaxation of the thoracic aorta preparation of SHRSP by acetylcholine was much less (ca 38%) than that of WKY; however, that of SHRSP by glyceryltrinitrate was slightly less (ca 74%), indicating that endothelium-dependent relaxation declined in vascular preparation of SHRSP. 4. The present results suggest that endothelium-dependent relaxation has some contribution on blood pressure regulation in the hypertensive state, although a decline of endothelium-dependent relaxation is evident in vascular preparation of SHRSP compared with WKY.

Topics: Acetylcholine; Administration, Oral; Animals; Arginine; Blood Pressure; Endothelium, Vascular; Female; Hypertension; Muscle, Smooth, Vascular; Nitroarginine; Nitroglycerin; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Vasoconstriction