calcimycin and Hypertension

1. Experimental hypertension is associated with several functional alterations of vascular endothelium and smooth muscle, but relatively few studies have examined the control of arterial tone in isolated vascular preparations from patients with essential hypertension. Therefore, we compared functional characteristics in vitro of distal ring segments of the mesenteric artery from 17 hypertensive and 22 normotensive humans. 2. Arterial constrictor responses induced by cumulative addition of Ca(2+) in the presence of noradrenaline (NA) were more effectively inhibited by the Ca(2+) entry blocker nifedipine (0.5 nM) in hypertensive than normotensive subjects (by 55.4+/-4.9, n=17 and 35.0+/(-5.2%), n=22, respectively). Also the contractions elicited by high concentrations of KCl were more effectively inhibited by nifedipine in arterial rings from hypertensive than normotensive patients (by 38.9+/(-3.7), n=17 and 20. 2+/(-4.6%), n=22, respectively). However, the concentration-response curves of contractions to NA, serotonin and KCl in the absence of nifedipine were similar between the study groups. 3. The concentration-response curves of endothelium-dependent relaxations to acetylcholine and Ca(2+) ionophore A23187, as well as of endothelium-independent relaxations to the nitric oxide donor nitroprusside, beta-adrenoceptor agonist isoprenaline and K+ channel opener cromakalim did not show any differences between the groups. Moreover, the nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester (0.1 mM) almost abolished the relaxations to acetylcholine and Ca(2+) ionophore in both groups, indicating that these responses were largely mediated by nitric oxide. The function of arterial sodium pump was evaluated by relaxations elicited by the return of K+ upon contractions induced by K+-free solution. The rate of K+-relaxation was similar in hypertensive and normotensive arteries (for all these responses n=20 - 22 in the normotensive and 15 - 17 in the hypertensive group). 4. These results suggest abnormal function of voltage-dependent Ca(2+) channels in arterial smooth muscle of hypertensive patients, whereas vascular responses to endothelium-dependent and -independent vasodilators and classical contractile agents were similar between hypertensive and normotensive subjects. The present findings support the view that blockade of voltage-dependent Ca(2+) channels is an effective means of reducing arterial tone in essential hypertension.

Topics: Adult; Aged; Aged, 80 and over; Calcimycin; Calcium Channel Blockers; Endothelium, Vascular; Enzyme Inhibitors; Female; Humans; Hypertension; In Vitro Techniques; Male; Mesenteric Arteries; Middle Aged; Muscle Tonus; Muscle, Smooth, Vascular; NG-Nitroarginine Methyl Ester; Nifedipine; Norepinephrine; Potassium; Serotonin; Vasoconstrictor Agents

K2P6.1 or TWIK-2, a two-pore domain K channel, is an important regulator of cardiovascular function. K2P6.1 is highly expressed in vascular smooth muscle and endothelium. Mice (8-12 wk) lacking functional K2P6.1 (K2P6.1(-/-)) are hypertensive and have enhanced vascular contractility. It is not known whether the lack of functional K2P6.1 in endothelium has a role in the vascular dysfunction in K2P6.1(-/-) mice. We tested the hypothesis: K2P6.1(-/-) mice have impaired endothelium-dependent relaxations. K2P6.1(-/-) mice were ∼35 mmHg more hypertensive than WT mice at both 8-12 wk (young adult) and 20-24 wk (mature mice, P < 0.01; n = 8-10). Endothelium-dependent relaxations of the thoracic aorta were evaluated by isometric myography after contraction with phenylephrine (10(-6) M). Maximal ACh-dependent relaxations were increased from 65 ± 1% to 73 ± 1% in the aorta from young adult (P < 0.01; n = 6) and from 45 ± 1% to 74 ± 1% in the aorta from mature (P < 0.001; n = 5) K2P6.1(-/-) mice compared with K2P6.1(+/+) littermates. However, in the aorta from young adult and mature K2P6.1(+/+) mice, 10(-5) M indomethacin, a cyclooxygenase inhibitor, increased maximal ACh relaxations to knockout levels. Enhanced relaxation was also seen with ATP, a P2Y purinergic agonist, and A23187, a nonreceptor-based agonist in mature K2P6.1(-/-) mice. Mature adult aorta from K2P6.1(-/-) showed an attenuated ACh-mediated contraction in the presence of nitro-l-arginine methyl ester (l-NAME) and without precontraction of 0.97 mN vs. 7.5 mN in K2P6.1(-/-) and K2P6.1(+/+) (P < 0.001; n = 5). In summary, K2P6.1(-/-) mice, which are hypertensive, have enhanced endothelium-dependent relaxations in the aorta due to the suppression of an indomethacin-sensitive constrictor component.

Topics: Animals; Aorta, Thoracic; Calcimycin; Disease Models, Animal; Endothelium, Vascular; Hypertension; Indomethacin; Male; Mice; Mice, Knockout; NG-Nitroarginine Methyl Ester; Phenylephrine; Potassium Channels, Tandem Pore Domain; Vasoconstriction; Vasodilation

Phospholipase A(2) (PLA(2)), a regulatory enzyme found in most mammalian cells, catalyzes the breakdown of membrane phospholipids to arachidonic acid. There are two major cytosolic types of the enzyme, calcium-dependent (cPLA(2)) and calcium-independent (iPLA(2)) PLA(2). The present study investigated whether or not iPLA(2) plays a role in the endothelium-dependent contractions of the aorta of the spontaneously hypertensive rat and its normotensive counterpart, the Wistar-Kyoto rat. The presence of iPLA(2) in the endothelial cells was identified by using immunochemistry and immunoblotting. Aortic rings with and without the endothelium were suspended in organ chambers for isometric tension recording. The production of prostanoids was measured by using enzyme immunoassay kits. iPLA(2) was densely distributed in endothelial cells of the aorta of both strains. At 3 x 10(-6) M, the selective iPLA(2) inhibitor, bromoenol lactone (BEL), abrogated endothelium-dependent contractions induced by acetylcholine but not those evoked by the calcium ionophore A-23187. The effects of BEL were similar in the aortae of Wistar-Kyoto and spontaneously hypertensive rats. The nonselective PLA(2) inhibitor quinacrine abolished the contractions triggered by both acetylcholine and A-23187, whereas the store-operated calcium channel inhibitor SKF-96365 prevented only the acetylcholine-induced contraction. The acetylcholine- but not the A-23187-induced release of 6-keto prostaglandin F(1alpha) was inhibited by BEL. The release of thromboxane B(2) by either acetylcholine or A-23187 was not affected by BEL. In conclusion, iPLA(2) plays a substantial role in the generation of endothelium-derived contracting factor evoked by acetylcholine.

Topics: Acetylcholine; Animals; Aorta; Calcimycin; Disease Models, Animal; Endothelium, Vascular; Hypertension; Imidazoles; Ionophores; Male; Muscle Contraction; Muscle, Smooth, Vascular; Naphthalenes; Phosphodiesterase Inhibitors; Phospholipases A2, Calcium-Independent; Pyrones; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Vasodilator Agents

Experiments were designed to determine the effect of gap junction inhibitors on endothelium-dependent contractions. Isolated aortic rings of spontaneously hypertensive rats (SHR) were suspended in vitro for isometric force recording. The nonselective gap junction inhibitor, carbenoxolone, reduced endothelium-dependent contractions to acetylcholine and the calcium ionophore A23187 [5-methylamino-2-(2S,3R,5R,8S,9S)-3,5,9-trimethyl-2-(1-oxo-(1H-pyrrol-2-yl)propan-2-yl)-1,7-dioxaspiro-(5,5)undecan-8-yl)methyl)benzooxazole-4-carboxylic acid]. There was no or modest effect of the gap peptides (40)Gap27, (37,43)Gap27, or (43)Gap26 when applied alone on endothelium-dependent contractions. However, the combined treatment with the three gap peptides significantly decreased endothelium-dependent contractions. The combined inhibition of the three connexins was not as effective as carbenoxolone, suggesting the involvement of other connexins in the process of endothelium-dependent contraction. The present study shows the involvement of gap junctions in endothelium-dependent contractions of the SHR aorta, presumably that of the combination of connexins 37, 40, and 43 rather than a single subtype of these proteins. Contractions of the vascular smooth muscle caused by 9,11-dideoxy-11alpha, 9alpha-epoxymethanoprostaglandin F(2alpha) (U46619) and prostacyclin, but not to those of endoperoxides and phenylephrine, were reduced only minimally by carbenoxolone. Thus, if gap junction signaling is involved in the contraction of the vascular smooth muscle to thromboxane-prostanoid receptor agonists, their contribution is small. This suggests that the reduction of endothelium-dependent contractions by carbenoxolone and the gap peptides cannot be attributed to the homocellular gap junctions between vascular smooth muscle, but is more likely to involve the homocellular gap junctions between endothelial cells and/or myoendothelial gap junctions.

Topics: Acetylcholine; Animals; Aorta, Thoracic; Calcimycin; Carbenoxolone; Connexins; Endothelium, Vascular; Estradiol; Gap Junctions; Hypertension; In Vitro Techniques; Rats; Rats, Inbred SHR; Reactive Oxygen Species; Receptors, Thromboxane; Vasoconstriction

The available evidence suggests that vitamin D has cardiovascular effects besides regulating calcium homeostasis. To examine the effect of 1,25-dihydroxyvitamin D(3), the major metabolite of vitamin D, on endothelium-dependent contractions, aortic rings of spontaneously hypertensive rats (SHR) were suspended in organ chambers for isometric force measurements. Rings were incubated with N(omega)-nitro-l-arginine methyl ester (l-NAME) and then exposed to increasing concentrations of acetylcholine, ATP, or the calcium ionophore to trigger contractions. This was done in the absence or presence of 1,25-dihydroxyvitamin D(3). The release of prostacyclin after acetylcholine or A-23187 stimulation was also measured. The cytosolic-free calcium concentration was measured by confocal microscopy after incubation with the fluorescent dyes fluo-4 and fura red. The presence of vitamin D receptors was confirmed using immunohistochemistry. Acetylcholine- and ATP-induced endothelium-dependent contractions were significantly reduced compared with those obtained in the absence of the drug. This effect was not present if A-23187 was used as an agonist. The acetylcholine- but not the A-23187-induced release of prostacyclin was reduced by the acute administration of 1,25-dihydroxyvitamin D(3). Exposure to 1,25-dihydroxyvitamin D(3) reduced the increase in cytosolic-free calcium concentration caused by acetylcholine but not by A-23187 in cells. Vitamin D receptors were densely distributed in the endothelium. Inecalcitol (19-nor-14-epi-23-yne-1,25-dihydroxyvitamin D(3)), a synthetic analog of vitamin D, caused a comparable depression of endothelium-dependent contractions as 1,25-dihydroxyvitamin D(3). These results demonstrate that vitamin D(3) modulates vascular tone by reducing calcium influx into the endothelial cells and hence decreasing the production of endothelium-derived contracting factors.

Topics: Acetylcholine; Adenosine Triphosphate; Animals; Calcimycin; Calcitriol; Calcium; Disease Models, Animal; Dose-Response Relationship, Drug; Endothelium, Vascular; Epoprostenol; Hypertension; Immunohistochemistry; Microscopy, Confocal; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Receptors, Calcitriol; Vasoconstriction; Vasoconstrictor Agents; Vitamin D

Angiotensin II (Ang II) exerts deleterious effect on the cerebral circulation through production of reactive oxygen species (ROS). However, the enzymatic source of the ROS has not been defined. We tested the hypothesis that Ang II impairs endothelium-dependent responses in the cerebral microcirculation through ROS generated in cerebrovascular cells by the enzyme NADPH oxidase.. Cerebral blood flow (CBF) was monitored by laser Doppler flowmetry in anesthetized mice equipped with a cranial window. Ang II (0.25+/-0.02 microg/kg per minute for 30 to 45 minutes) attenuated the CBF increase produced by the endothelium-dependent vasodilators acetylcholine (-42+/-5%; P<0.05), bradykinin (-53+/-5%; P<0.05), and A23187 (-43+/-4%; P<0.05), and induced cerebrovascular ROS production, assessed by hydroethidine fluoromicrography. These actions of Ang II were prevented by losartan, by the ROS scavenger Mn(III) tetrakis (4-benzoic acid) porphyrin chloride (100 micromol/L), or by the NADPH oxidase peptide inhibitor gp91ds-tat (1 micromol/L), and were not observed in mice lacking the NADPH oxidase subunit gp91phox (nox-2).. Ang II impairs the endothelial regulation of the cerebral microcirculation through AT1 receptor-mediated cerebrovascular oxidative stress. The source of the ROS is a nox-2-containing NADPH oxidase. These effects of Ang II could threaten the cerebral blood supply and contribute to the increased susceptibility to stroke and dementia associated with hypertension.

Topics: Acetylcholine; Angiotensin II; Animals; Bradykinin; Calcimycin; Cerebrovascular Circulation; Endothelium, Vascular; Hypertension; Membrane Glycoproteins; Mice; NADPH Oxidase 2; NADPH Oxidases; Oxidative Stress; Reactive Oxygen Species; Receptor, Angiotensin, Type 1; Signal Transduction

Recent in vitro studies have shown that disturbed flow and oxidative conditions induce the expression of bone morphogenic proteins (BMPs 2 and 4) in cultured endothelial cells. BMPs can stimulate superoxide production and inflammatory responses in endothelial cells, raising the possibility that BMPs may play a role in vascular diseases such as hypertension and atherosclerosis. In this study, we examined the hypothesis that BMP4 would induce hypertension in intact animals by increasing superoxide production from vascular nicotinamide adenine dinucleotide phosphate (NADPH) oxidases and an impairment of vasodilation responses.. BMP4 infusion by osmotic pumps increased systolic blood pressure in a time- and dose-dependent manner in both C57BL/6 mice (from 101 to 125 mm Hg) and apolipoprotein E-null mice (from 107 to 146 mm Hg) after 4 weeks. Cotreatment with the BMP antagonist noggin or the NADPH oxidase inhibitor apocynin completely blocked the BMP4 effect. In addition, BMP4 infusion stimulated aortic NADPH oxidase activity and impaired vasorelaxation, both of which were prevented either by coinfusing noggin or by treating the isolated aortas with apocynin. BMP4, however, did not cause significant changes in maximum relaxation induced by the endothelium-independent vasodilator nitroglycerin. Remarkably, BMP4 infusion failed to stimulate aortic NADPH oxidases, increase blood pressure, and impair vasodilation responses in p47phox-deficient mice.. These results suggest that BMP4 infusion induces hypertension in mice in a vascular NADPH oxidase-dependent manner and the subsequent endothelial dysfunction. We suggest that BMP4 is a novel mediator of endothelial dysfunction and hypertension and that noggin and its analogs could be used as therapeutic agents for treating vascular diseases.

Topics: Acetophenones; Acetylcholine; Animals; Aorta, Thoracic; Apolipoproteins E; Bone Morphogenetic Protein 4; Bone Morphogenetic Proteins; Calcimycin; Carrier Proteins; Diet, Atherogenic; Endothelium, Vascular; Enzyme Activation; Humans; Hyperlipoproteinemia Type II; Hypertension; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; NADPH Oxidases; Nitroglycerin; Recombinant Fusion Proteins; Superoxides; Vasodilator Agents

In mature spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY), acetylcholine and the calcium ionophore A-23187 release endothelium-derived contracting factors (EDCFs), cyclooxygenase derivatives that activate thromboxane-endoperoxide (TP) receptors on vascular smooth muscle. The EDCFs released by acetylcholine are most likely prostacyclin and prostaglandin (PG)H(2), whereas those released by A-23187 remain to be identified. Isometric tension and the release of PGs were measured in rings of isolated aortas of WKY and SHR. A-23187 evoked the endothelium-dependent release of prostacyclin, thromboxane A(2), PGF(2alpha), PGE(2), and possibly PGH(2) (PGI(2) >> thromboxane A(2) = PGF(2alpha) = PGE(2)). In SHR aortas, the release of prostacyclin and thromboxane A(2) was significantly larger in response to A-23187 than to acetylcholine. In response to the calcium ionophore, the release of thromboxane A(2) was significantly larger in aortas of SHR than in those of WKY. In both strains of rat, the inhibition of cyclooxygenase-1 prevented the release of PGs and the occurrence of endothelium-dependent contractions. Dazoxiben, the thromboxane synthase inhibitor, abolished the A-23187-dependent production of thromboxane A(2) and inhibited by approximately one-half the endothelium-dependent contractions. U-51605, an inhibitor of PGI synthase, reduced the release of prostacyclin elicited by A-23187 but induced a parallel increase in the production of PGE(2) and PGF(2alpha), suggestive of a PGH(2) spillover, which was associated with the enhancement of the endothelium-dependent contractions. These results indicate that in the aorta of SHR and WKY, the endothelium-dependent contractions elicited by A-23187 involve the release of thromboxane A(2) and prostacyclin with a most likely concomitant contribution of PGH(2).

Topics: Animals; Aorta, Thoracic; Calcimycin; Dose-Response Relationship, Drug; Endothelium, Vascular; Epoprostenol; Hypertension; In Vitro Techniques; Ionophores; Male; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Thromboxane A2; Vasoconstriction

We tested the activity of nebivolol, a beta1-selective blocker with respect to nitric oxide (NO) and peroxynitrite (ONOO) generation in the endothelium of normotensive Wistar Kyoto (WKY rats) and spontaneously hypertensive rats (SHR). The endothelial effects of nebivolol and its 2 optical enantiomers were correlated with its antioxidant activity and compared to another beta-blocker, atenolol, and 2 agonists of nitric oxide synthase (eNOS), calcium ionophore (CI) and acetylcholine (ACh). The effects of nebivolol on the bioavailability of NO and ONOO, indicators of endothelial function and dysfunction, respectively, were measured in vitro using nanosensors placed in mesenteric arteries. Compared with WKY rats, treatment of SHR vessels either with ACh (1 micromol/L) or CI (1 micromol/L) showed marked deficiencies (>40%, P < 0.01) in bioavailable NO concomitant with increased ONOO levels (>50%, P < 0.01). The [NO]/[ONOO] ratio measured after stimulation with CI was 2.77 +/- 0.05 in WKY rats and much lower (1.14 +/- 0.11) in SHR indicating significant eNOS uncoupling and endothelial dysfunction in hypertensive animals. Treatment with nebivolol (10 micromol/L) inhibited eNOS uncoupling and reduced endothelial dysfunction in SHR, as evidenced by an increase in the [NO]/[ONOO] ratio to 3.09 +/- 0.04. The basis for nebivolol activity is attributed to its unique membrane interactions as determined by small-angle x-ray diffraction, as well as its antioxidant activity at nanomolar to micromolar levels. The antioxidant effects of nebivolol and its enantiomers were not reproduced by atenolol. These results demonstrate that nebivolol inhibits endothelial dysfunction through a potent antioxidant mechanism attributed to its physicochemical interactions with the membrane, independent of beta1-blockade activity.

Topics: Acetylcholine; Animals; Antihypertensive Agents; Antioxidants; Atenolol; Benzopyrans; Calcimycin; Dose-Response Relationship, Drug; Endothelium, Vascular; Ethanolamines; Female; Fourier Analysis; Hypertension; Lipid Bilayers; Lipid Peroxidation; Male; Mesenteric Arteries; Nanotechnology; Nebivolol; Nitric Oxide; Peroxynitrous Acid; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Solubility; Stereoisomerism; X-Ray Diffraction

Insulin decreased A23187-induced hyperpolarization of the erythrocyte membrane in healthy donors. These data indicate that insulin plays a role in the regulation of Ca(2+)-activated potassium channels in human erythrocytes. However, insulin had little effect on hyperpolarization response of cells induced by artificial ascorbate--phenazine methosulfate donor-acceptor system. Addition of insulin to cell suspension from patients with type 2 diabetes mellitus did not modulate hyperpolarization of the erythrocyte membrane induced by A23187 or ascorbate-phenazine methosulfate, which reflects impairment of regulatory mechanisms for Ca(2+)-activated potassium channels in erythrocytes.

Topics: Arteries; Ascorbic Acid; Calcimycin; Calcium; Carbonyl Cyanide m-Chlorophenyl Hydrazone; Case-Control Studies; Diabetes Mellitus, Type 2; Erythrocytes; Female; Humans; Hydrogen-Ion Concentration; Hypertension; Insulin; Ionophores; Male; Methylphenazonium Methosulfate; Oxidation-Reduction

Increase in intracellular Ca2+ concentration caused by calcium ionophore A23187 or ascorbate+phenazine methosulphate electron donor system added to erythrocyte suspension induced similar shifts in erythrocyte membrane potential. These processes are most likely mediated by Ca2+-activated potassium channels. Changes in the osmolarity of the incubation medium produced opposite effects on membrane hyperpolarization induced by A23187 or ascorbate+phenazine methosulphate in erythrocyte isolated from healthy donors, which attests to the existence of different mechanisms of regulation of Ca2+-activated potassium channels. There was no difference in the volume-dependent changes of potassium permeability in cells from patients with type II diabetes mellitus combined with arterial hypertension induced by application A23187 or electron-donor system.

Topics: Calcimycin; Diabetes Mellitus, Type 2; Erythrocyte Membrane; Erythrocytes; Humans; Hypertension; Membrane Potentials; Osmolar Concentration; Potassium Channels, Calcium-Activated

Cadmium (Cd) toxicity was produced in male rats to study the role of cholinoceptors in Cd-induced endothelial dysfunction. The changes in the tension of the aortic rings to constrictor and dilator agonists were compared with those of controls. A Cd-induced significant increase in phenylephrine response was associated with a decrease in basal dilator prostanoid release. In Cd-exposed rings, despite an obvious depression in the acetylcholine (ACh) response, the receptor-independent dilation to the calcium ionophore A23187, which elicits a receptor-independent endothelial relaxation, was slightly elevated (p<0.01), but the smooth muscle cell response to the NO donor, sodium nitroprusside (SNP) remained unaltered. Cadmium decreased both the maximal response to ACh (10(-5) M) and its pirenzepine (Prz) sensitive component. The M1 type cholinoceptor-mediated response to ACh decreased in Cd-exposed rings to 10.30 +/- 5.00% from 38.40 +/- 6.90% (p<0.001). Cadmium also reduced the share of indomethacin 1.64% to 13.92 +/- 2.89% (p<0.01), which correlated well with the changes in the M1-mediated response (r=0.991, p<0.0001). Most of the deleterious effect of Cd appears to be restricted to the M1-dependent ACh response. These findings suggest that Cd produces an endothelial dysfunction by impairing the M1 type cholinoceptor mediated response, which seems to be involved in prostanoid release.

Topics: Acetylcholine; Administration, Oral; Animals; Aorta, Thoracic; Atropine; Cadmium; Calcimycin; Dose-Response Relationship, Drug; Drug Synergism; Endothelium, Vascular; Gallamine Triethiodide; Glomerular Filtration Rate; Hypertension; Indomethacin; Kidney Cortex; Kidney Diseases; Male; Muscle Contraction; Muscle, Smooth, Vascular; NG-Nitroarginine Methyl Ester; Nitroprusside; Peripheral Vascular Diseases; Phenylephrine; Pirenzepine; Prostaglandins; Rats; Rats, Wistar; Receptor, Muscarinic M1; Vasodilation

To investigate the effect of a chronic treatment with melatonin on arterial pressure and a possible improvement of the vascular muscarinic and NO synthase (NOS) pathways in spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats.. Mean arterial pressure (MAP), systolic (SBP), diastolic blood pressure (DBP), and heart rate (HR) were evaluated in conscious rats treated with 30 mg/kg per day of melatonin during 4 weeks. Changes in MAP were evaluated following an intravenous injection of the NOS inhibitor N-omega-nitro-L-arginine methyl ester (L-NAME). Relaxant effects of acetylcholine (Ach), sodium nitroprusside (SNP), and the calcium ionophore A23187 were examined on mesenteric beds and aortic rings with or without treatment with melatonin.. Melatonin produced a significant reduction of MAP, SBP, DBP and HR in SHR (P < 0.05). L-NAME increased the MAP of melatonin-treated SHR by the same magnitude as that of WKY rats which was significantly higher than that of non-treated SHR (P< 0.05). Melatonin treatment improved the maximal relaxation of mesenteric arteries to A23187 in SHR (P < 0.001) to the WKY level and caused a slight increment in Ach- and A23187-induced vasodilations in aorta from SHR and WKY rats (P < 0.05).. The present study showed that melatonin exerted a bradycardic and an antihypertensive action in SHR. The enhancement by melatonin of the endothelium-dependent vasodilation (Ach and/or A23187) in mesenteric artery and aorta from SHR and WKY rats and the higher increase in MAP following L-NAME treatment in melatonin-treated SHR suggest the contribution of an improved vascular NOS pathway activity in the hypotensive effect of melatonin.

Topics: Acetylcholine; Animals; Antihypertensive Agents; Aorta; Blood Pressure; Body Weight; Calcimycin; Enzyme Inhibitors; Hypertension; Ionophores; Male; Melatonin; Mesenteric Arteries; NG-Nitroarginine Methyl Ester; Nitroprusside; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Time Factors; Vasodilation; Vasodilator Agents; Vasomotor System

1. Cyclic guanosine monophosphate (cyclic GMP)-mediated mechanism plays an important role in vasodilatation and blood pressure regulation. We investigated the effects of high salt intake on the nitric oxide (NO) - cyclic GMP signal transduction pathway regulating relaxation in aortas of spontaneously hypertensive rats (SHR). 2. Four-week-old SHR and normotensive Wistar-Kyoto rats (WKY) received a normal salt diet (0.3% NaCl) or a high salt diet (8% NaCl) for 4 weeks. 3. In aortic rings from SHR, endothelium-dependent relaxations in response to acetylcholine (ACh), adenosine diphosphate (ADP) and calcium ionophore A23187 were significantly impaired by the high salt intake. The endothelium-independent relaxations in response to sodium nitroprusside (SNP) and nitroglycerin were also impaired, but that to 8-bromo-cyclic GMP remained unchanged. On the other hand, high salt diet had no significant effects on the relaxations of aortic rings from WKY. 4. In aortas from SHR, the release of NO stimulated by ACh was significantly enhanced, whereas the production of cyclic GMP induced by either ACh or SNP was decreased by the high salt intake. 5. Western blot analysis showed that the protein level of endothelial NO synthase (eNOS) was slightly increased, whereas that of soluble guanylate cyclase (sGC) was dramatically reduced by the high salt intake. 6. These results indicate that in SHR, excessive dietary salt can result in downregulation of sGC followed by decreased cyclic GMP production, which leads to impairment of vascular relaxation in responses to NO. It is notable that chronic high salt intake impairs the sGC/cyclic GMP pathway but not the eNOS/NO pathway.

Topics: Acetylcholine; Adenosine Diphosphate; Animals; Aorta, Thoracic; Blood Pressure; Calcimycin; Cyclic GMP; Dose-Response Relationship, Drug; Down-Regulation; Endothelium, Vascular; Guanylate Cyclase; Heart Rate; Hypertension; In Vitro Techniques; Ionophores; Male; Nitric Oxide; Nitric Oxide Synthase; Nitric Oxide Synthase Type III; Nitroglycerin; Nitroprusside; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Sodium Chloride, Dietary; Solubility; Species Specificity; Vasodilation; Vasodilator Agents

To investigate the effect of ouabain on inducible nitric oxide synthase (iNOS) activity and expression in cytokine-stimulated vascular smooth muscle cells (VSMC) from normotensive Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR).. VSMC were treated for 24 h and afterwards, nitric oxide (NO) release was determined by the production of nitrite, a stable metabolite of NO. Activity of iNOS was measured by the conversion of [3H]-L-arginine to [3H]-L-citrulline and iNOS protein expression by Western blotting.. Ouabain (0.01-1 mmol/l) further enhanced interleukin-1beta (II-1beta)-induced nitrite production by WKY and SHR VSMC, although a more pronounced effect was observed in SHR cells (maximum response 52.1 +/- 5.2 and 71.2 +/- 6.4% of 11-1beta effect in WKY and SHR cells, respectively). Such response on NO release was mimicked by the calcium ionophore A 23187 (0.01-1 micromol/l) and abolished by the voltage-operated calcium channels (VOCC) nifedipine (0.1 micromol/l). Expression of iNOS showed that ouabain increased the synthesis of the enzyme in WKY and SHR VSMC stimulated with II-1beta, and this effect was higher in SHR cells. The increased iNOS expression was significantly reduced by nifedipine.. Ouabain stimulation of iNOS expression and activity in II-1beta-stimulated VSMCs from WKY rats and SHR seems to be related to increased intracellular calcium influx through VOCC. The more pronounced effect observed in SHR VSMC could be explained by an altered calcium entry in the hypertensive strain.

Topics: Animals; Blotting, Western; Calcimycin; Calcium; Calcium Channel Blockers; Cells, Cultured; Enzyme Induction; Enzyme Inhibitors; Hypertension; Interleukin-1; Intracellular Fluid; Ionophores; Muscle, Smooth, Vascular; Nifedipine; Nitric Oxide Synthase; Nitric Oxide Synthase Type II; Ouabain; Rats; Rats, Inbred SHR; Rats, Wistar

It has been shown that rheological abnormality might be an etiological factor in hypertension. Recent studies have revealed that human erythrocytes possess a nitric oxide (NO) synthase and that this activation might be involved in the regulation of rheological properties of erythrocytes. The present study was undertaken to investigate the role of NO in the regulation of membrane functions of erythrocytes in patients with essential hypertension by means of an electron paramagnetic resonance (EPR) and spin-labeling method. The NO donor S-nitroso-N-acetylpenicillamine (SNAP) decreased the order parameter (S) for 5-nitroxide stearate (5-NS) and the peak height ratio (h(0)/h(-1)) for 16-NS obtained from EPR spectra of erythrocyte membranes in a dose-dependent manner. The finding indicated that the NO donor increased the membrane fluidity of erythrocytes. In addition, the effect of SNAP was significantly potentiated by 8-bromo-cyclic guanosine monophosphate. By contrast, the change of the fluidity induced by SNAP was reversed in the presence of L-N(G)-nitroarginine methyl ester and asymmetric dimethyl L-arginine. In patients with essential hypertension, the membrane fluidity of erythrocytes was significantly lower than in the normotensive subjects. The effect of SNAP was more pronounced in essential hypertension than in normotensive subjects. These results showed that NO increased the membrane fluidity and decreased the rigidity of cell membranes. Furthermore, the greater effect of NO on the fluidity in essential hypertension suggests that NO might actively participate in the regulation of rheological behavior of erythrocytes and have a crucial role in the improvement of microcirculation in hypertension.

Topics: Arginine; Blood Pressure; Calcimycin; Cell Membrane; Cyclic GMP; Cyclic N-Oxides; Electron Spin Resonance Spectroscopy; Erythrocytes; Hemorheology; Humans; Hypertension; Membrane Fluidity; Middle Aged; NG-Nitroarginine Methyl Ester; Nitric Oxide; Nitric Oxide Donors; Nitric Oxide Synthase; Penicillamine; Spin Labels

Adrenomedullin is a newly discovered 52 amino acid peptide that has a potent vasodilating action. The present study was undertaken to investigate the role of adrenomedullin in the regulation of membrane fluidity of erythrocytes in patients with essential hypertension.. We used an electron paramagnetic resonance and spin-labeling method. Adrenomedullin significantly decreased the order parameter for 5-nitroxide stearate and peak height ratio for 16-nitroxide stearate obtained from electron paramagnetic resonance spectra of erythrocyte membranes in normotensive volunteers (mean +/- SEM order parameter value: control, 0.718 +/- 0.003, n = 16; adrenomedullin at 10(-9) mol/l, 0.692 +/- 0.004, n = 16, P < 0.05; adrenomedullin at 10(-8) mol/l, 0.690 +/- 0.004, n = 16, P < 0.05; adrenomedullin at 10(-7) mol/l, 0.683 +/- 0.004, n = 16, P < 0.05). The findings showed that adrenomedullin increased the membrane fluidity of erythrocytes. In addition, the effect of adrenomedullin was significantly potentiated by prostaglandin E1 and dibutyryl cyclic AMP. In contrast, the calcium ionophore A23187 counteracted the actions of adrenomedullin. In patients with essential hypertension, who had higher order parameter values, the membrane fluidity of erythrocytes was significantly lower than in the normotensive control subjects (order parameter: 0.728 +/- 0.004 in hypertensives, n = 20; 0.692 +/- 0.002 in normotensives, n = 36, P < 0.01). The effect of adrenomedullin on membrane fluidity was more pronounced in the erythrocytes of essential hypertensive than in the erythrocytes of normotensive subjects (change in the order parameter with adrenomedullin at 10(-9) mol/l: -4.2 +/- 0.3% in hypertensives, n = 20; -1.8 +/- 0.2% in normotensives, n = 20, P < 0.05; adrenomedullin at 10(-8) mol/l: -4.5 +/- 0.3% in hypertensives, n = 20; -1.8 +/- 0.2% in normotensives, n = 36, P < 0.05).. The results of the present study demonstrate that adrenomedullin significantly increased the membrane fluidity of erythrocytes. The mechanisms were partially mediated by a prostaglandin E1- and cyclic AMP-dependent pathway which might be linked to changes in intracellular calcium kinetics. The greater effect of adrenomedullin in patients with essential hypertension suggests that the peptide might actively participate in the regulation of membrane functions in hypertension.

Topics: Adrenomedullin; Alprostadil; Bucladesine; Calcimycin; Calcium; Cyclic N-Oxides; Drug Combinations; Electron Spin Resonance Spectroscopy; Erythrocytes; Female; Humans; Hypertension; Male; Membrane Fluidity; Middle Aged; Peptides; Spin Labels; Vasodilator Agents

Constitutive nitric oxide synthase (cNOS) with insufficient cofactor (6R)-5,6,7,8-tetrahydrobiopterin (H4B) may generate damaging superoxide (O2-). This study was designed to determine whether cNOS-dependent generation of O2- occurs in spontaneously hypertensive rats (SHR) before the onset of hypertension. Aortas from 4-wk-old SHR and Wistar-Kyoto rats were used. cNOS was stimulated by calcium ionophore A23187. In situ measurements of nitric oxide and hydrogen peroxide by electrochemical sensors and O2- production by chemiluminescence method were performed. Isometric tension was continuously recorded. H4B by high performance liquid chromatography and [3H]citrulline assay were determined in homogenized tissue. The A23187-stimulated production of O2- and its superoxide dismutase product hydrogen peroxide were significantly higher, whereas nitric oxide release was reduced in SHR aortas, with opposite results in the presence of exogenous H4B. Furthermore, NG-monomethyl-L-arginine inhibited the generation of cNOS-dependent O2- by approximately 70%. Natural H4B levels were similar in both strains; however, equivalent cNOS activity required additional H4B in SHR. The endothelium-dependent relaxations to A23187 were significantly inhibited by catalase, and enhanced by superoxide dismutase, only in SHR; however, these enzymes had no effect in the presence of H4B. Thus, dysfunctional cNOS may be a source of O2- in prehypertensive SHR and contribute to the development of hypertension and its vascular complications.

Topics: Animals; Aorta; Biopterins; Calcimycin; Dose-Response Relationship, Drug; Endothelium, Vascular; Hydrogen Peroxide; Hypertension; In Vitro Techniques; Ionophores; Nitric Oxide; Nitric Oxide Synthase; Nitroprusside; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Superoxides; Vasomotor System

The objective of this study was to determine the contribution of renal nerves to the enhanced afferent arteriolar reactivity observed in angiotensin II (Ang II)-induced hypertension. Uninephrectomized Sprague-Dawley rats were divided into four groups: sham rats, renal-denervated rats, Ang II-infused (at 40 ng/min for 13 days) rats, and Ang II-infused+renal-denervated rats. With the use of an implanted arterial catheter, mean arterial pressure (MAP) was monitored in conscious rats. Ang II infusion resulted in a progressive increase in MAP from 98 +/- 1 (day 0) to 166 +/- 7 mm Hg (day 13). This increase in MAP was attenuated in denervated rats and averaged 136 +/- 3 mm Hg on day 13. Kidneys were harvested on day 13 for microcirculatory experiments or measurement of intrarenal Ang II levels. Basal afferent arteriolar diameter was similar in all groups, and group averages ranged from 19.6 to 20.7 microns. Chronic Ang II infusion increased intrarenal Ang II levels. Renal denervation did not alter this effect. Increasing perfusion pressure from 100 to 160 mm Hg reduced afferent arteriolar diameter significantly by 11.2 +/- 0.6% in the sham group and by a similar degree in the remaining three groups. Superfusion with Ang II (10 nmol/L) reduced afferent arteriolar diameter by 34.3 +/- 2.0% in the sham group. This response was enhanced in Ang II-infused (62.3 +/- 3.4%) but not in renal-denervated or Ang II-infused+renal-denervated rats. Additionally, the enhanced afferent arteriolar reactivity to Ang II was not influenced by adrenergic receptor blockade. The afferent arteriolar response to norepinephrine was enhanced in renal-denervated, Ang II-infused, and Ang II-infused+renal-denervated rats compared with sham controls. Administration of the calcium ionophore A23187 decreased afferent arteriolar diameter similarly in all four groups. These results indicate that renal nerves contribute to the development of hypertension and to the enhanced afferent arteriolar responsiveness to Ang II elicited by chronic Ang II infusion.

Topics: Angiotensin II; Animals; Arterioles; Blood Pressure; Calcimycin; Denervation; Hypertension; Kidney; Male; Norepinephrine; Rats; Rats, Sprague-Dawley; Sympathetic Nervous System; Vasoconstrictor Agents

This study investigated which subtype of muscarinic receptor in mesenteric arteries from SHRs mediates the loss of the release of nitric oxide (NO) or endothelium-derived hyperpolarizing factor (EDHF) in spontaneously hypertensive rats (SHRs) and Wistar-Kyoto (WKY) rats. After SHRs and WKY rats were killed, their superior mesenteric arteries were isolated to perform the vascular relaxation study. Acetylcholine (ACh, 1 nM-1 microM)-induced relaxation was in a concentration-dependent manner and was impaired in mesenteric arterial rings obtained from the SHR group, whereas nitroglycerin (10 nM-1 microM)-induced relaxation was not affected in endothelium-denuded rings obtained from the hypertensive rat. In the presence of N(omega)-nitro-L-arginine (L-NNA; 0.1 mM) or methylene blue (10 microM), the ACh-induced relaxation was partially attenuated in both SHRs and WKY rats. The relaxation of ACh was partially inhibited by 4-aminopyridine (4-AP; 1 mM), apamin (APM; 1 microM), or charybdotoxin (CTX; 0.1 microM) in WKY rats, whereas that relaxation was not affected by 4-AP, APM, or CTX in SHRs. However, the L-NNA-resistant relaxation of ACh was further inhibited by APM or CTX in WKY rats but not in SHRs. When arterial rings were precontracted by 60 mM K+, the ACh-induced relaxation was not significantly different in SHRs and WKY rats. However, this relaxation was abolished by L-NNA (0.1 mM) in both strains. In addition, the M3 muscarinic antagonist, 4-diphenylacetoxy-N-methylpiperidine was the most potent in inhibiting the relaxation of ACh, being more potent than pirenzepine and methoctramine, which preferentially block M1 and M2 receptors in the mesenteric artery of WKY rats, respectively. 2-Nitro-4-carboxyphenyl-N,N-diphenylcarbamate (1 microM) almost abolished the relaxation of ACh, but not of A23187, in SHRs and WKY rats. These results suggest that NO and EDHF are released from the endothelium of rat mesenteric artery on the activation of muscarinic M3-receptor by ACh, and the loss of ACh-induced relaxation in small arteries of SHRs is mainly through reducing the release or activity or both of EDHF.

Topics: Acetylcholine; Animals; Calcimycin; Enzyme Inhibitors; Hypertension; Ionophores; Male; Mesenteric Arteries; Methylene Blue; Muscarinic Agonists; Muscle Contraction; Muscle Relaxation; Muscle, Smooth, Vascular; Nitric Oxide Synthase; omega-N-Methylarginine; Purinergic P1 Receptor Antagonists; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Receptors, Muscarinic

Young (approximately 1 month old) male normotensive Wistar-Kyoto rats (n=26) and spontaneously hypertensive rats (n=38) were randomized into three groups treated via drinking water for approximately 2 years with, respectively, placebo, low doses, or high doses of an angiotensin-converting enzyme inhibitor, ramipril (10 microg x kg[-1] x d[-1], non-blood pressure-lowering dose, or 1 mg x kg[-1] x d[-1], blood pressure-lowering dose). Relative to placebo treatment in each respective rat strain, both ramipril dosages increased endothelial constitutive nitric oxide synthase expression (Western blot) and resultant synthesis of nitric oxide (porphyrinic sensor) in freshly excised carotids and thoracic aortas, respectively. Paradoxically, this activity was associated with an increased/decreased superoxide accumulation (chemiluminescence) in freshly excised aortas from 24-/22-month-old normotensive/hypertensive rats. In normotensive rats, relative to placebo treatment, the threefold increase in superoxide accumulation with antihypertensive ramipril treatment is most likely from the >300% increase in endothelial constitutive nitric oxide synthase expression (some of which may be disarranged by local insufficiencies in L-arginine or tetrahydrobiopterin). In hypertensive rats, relative to placebo treatment, the 35% increase in nitric oxide availability by long-term antihypertensive ramipril treatment may contribute to the preservation of the endothelium and prevent its dysfunction by inhibiting superoxide production. Increased nitric oxide production with concomitant decreased superoxide accumulation (approximately one third of placebo levels) correlates positively with the previously reported +40% life span extension for rats with genetic hypertension that were treated with antihypertensive doses of ramipril.

Topics: Angiotensin-Converting Enzyme Inhibitors; Animals; Aorta, Thoracic; Calcimycin; Carotid Arteries; Dose-Response Relationship, Drug; Hypertension; Male; Nitric Oxide; Nitric Oxide Synthase; Ramipril; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Reference Values; Superoxides

The endothelium plays a critical role in maintaining vascular tone by releasing vasoconstrictor and vasodilator substances. Endothelium-derived nitric oxide is a vasodilator that can be rapidly inactivated by superoxide (reaction rate constant, K = 3.6 x 10(9) L/mol per second). The measurement of nitric oxide concentration in biological systems is a challenging analytic problem because nitric oxide is also rapidly inactivated by Fe(II), Fe(III), and O2, all of which are found in great abundance in biological systems. To date, no currently used instrumental technique has been suitable for direct in situ measurement of NO in isolated resistance arteries. We designed the present study to perform for the first time direct in situ measurements of NO in rat mesenteric resistance arteries and to delineate the effects of hypertension on the release of NO and/or its interaction with superoxide. We describe here an adaptation of the recently published design of a porphyrinic sensor for direct in vitro measurement of NO in a single cell. The most significant advantage of this modified porphyrinic microsensor is that its small size makes it ideal for NO measurement in resistance arteries with an internal diameter of 200 microns or less. Small segments of the third-order branch of the mesenteric artery were isolated from normotensive Wistar-Kyoto rats and stroke-prone spontaneously hypertensive rats and placed in an organ chamber filled with Hanks' balanced salt solution buffer (2 mL, 37 degrees C). The tip of the porphyrinic microsensor was inserted into the lumen of an isolated vascular ring, and NO release was monitored in situ after maximal stimulation of NO synthase with the receptor-independent agonist calcium ionophore A23187 (10 mumol/L). Maximal surface concentration of NO measured after A23187 administration was significantly smaller in 15-week-old hypertensive rats (0.28 +/- 0.03 mumol/L, n = 10) than in age-matched normotensive rats (0.38 +/- 0.03 mumol/L, n = 10, P < .03). However, in the presence of the superoxide scavenger superoxide dismutase (100 U/mL), the peak NO level from the hypertensive rats was 0.37 +/- 0.04 mumol/L (n = 10), which was comparable to that observed for the normotensive rats in the absence and presence of superoxide dismutase. In summary, our results demonstrate that in rat mesenteric resistance arteries hypertension is associated with increased NO decomposition by superoxide, whereas NO release remains unaffected. This may be im

Topics: Animals; Body Weight; Calcimycin; Cerebrovascular Disorders; Genetic Predisposition to Disease; Hypertension; Male; Mesenteric Arteries; Nitric Oxide; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Superoxide Dismutase; Superoxides; Vascular Resistance

We tested the hypothesis that angiotensin II-induced hypertension is associated with an increase in vascular .O2- production, and characterized the oxidase involved in this process. Infusion of angiotensin II (0.7 mg/kg per d) increased systolic blood pressure and doubled vascular .O2- production (assessed by lucigenin chemiluminescence), predominantly from the vascular media. NE infusion (2.75 mg/kg per d) produced a similar degree of hypertension, but did not increase vascular .O2- production. Studies using various enzyme inhibitors and vascular homogenates suggested that the predominant source of .O2- activated by angiotensin II infusion is an NADH/NADPH-dependent, membrane-bound oxidase. Angiotensin II-, but not NE-, induced hypertension was associated with impaired relaxations to acetylcholine, the calcium ionophore A23187, and nitroglycerin. These relaxations were variably corrected by treatment of vessels with liposome-encapsulated superoxide dismutase. When Losartan was administered concomitantly with angiotensin II, vascular .O2- production and relaxations were normalized, demonstrating a role for the angiotensin type-1 receptor in these processes. We conclude that forms of hypertension associated with elevated circulating levels of angiotensin II may have unique vascular effects not shared by other forms of hypertension because they increase vascular smooth muscle .O2- production via NADH/NADPH oxidase activation.

Topics: Acetylcholine; Angiotensin II; Animals; Antihypertensive Agents; Aorta; Arginine; Biphenyl Compounds; Calcimycin; Endothelium, Vascular; Enzyme Activation; Enzyme Inhibitors; Hypertension; Imidazoles; In Vitro Techniques; Losartan; Male; Muscle Relaxation; Muscle Tonus; Muscle, Smooth, Vascular; NADH, NADPH Oxidoreductases; Nitric Oxide Synthase; Nitroglycerin; Norepinephrine; omega-N-Methylarginine; Rats; Rats, Sprague-Dawley; Superoxide Dismutase; Superoxides; Tetrazoles

We investigated the effect of hypercholesterolemia on the vascular reactivity of thoracic aortas isolated from hypertensive Dahl salt-sensitive (DS) rats. DS rats were fed on a low-sodium diet (control group), a low-sodium plus high-cholesterol diet (CHOL group), a high-sodium diet (NaCl group) or a high-sodium plus high-cholesterol diet (NaCl + CHOL group) for 8 weeks. Hypercholesterolemia developed in the CHOL and NaCl + CHOL groups, while hypertension developed in the NaCl and NaCl + CHOL groups, with these changes being greatest in the NaCl + CHOL group. Aortic cholesteryl ester accumulation was attenuated in the aortic rings from the NaCl and NaCl + CHOL groups, compared to the control group. The degree of attenuation in the NaCl + CHOL group was significantly greater than that in the NaCl group. Endothelium-dependent relaxations induced by the calcium ionophore A23187 were attenuated only in the NaCl + CHOL group. Endothelium-independent relaxations in response to sodium nitroprusside were slightly but significantly attenuated in the NaCl + CHOL group. The relaxations in the CHOL group were comparable to those in the control group. These findings indicate that cholesterol feeding strikingly enhances the impaired endothelium-dependent relaxations and the slightly impaired endothelium-independent relaxations in the aorta of DS rats with salt-induced hypertension, parallel to the development of hypertension, hypercholesterolemia and cholesterol deposition.

Topics: Acetylcholine; Animals; Antihypertensive Agents; Aorta, Thoracic; Calcimycin; Cholesterol Esters; Cholesterol, Dietary; Endothelium, Vascular; Hypercholesterolemia; Hypertension; Ionophores; Lipid Metabolism; Male; Muscle Relaxation; Muscle, Smooth, Vascular; Nitroprusside; Rats; Rats, Inbred Strains; Sodium, Dietary

Strips of tail artery from stroke-prone spontaneously hypertensive rats (SHRSP), but not from normotensive Wistar Kyoto (WKY) rats, exhibit oscillatory activity after stimulation with norepinephrine. In addition, oscillatory activity is observed in response to tetraethylammonium (TEA) in vessels from both SHRSP and WKY rats. Mechanistically, the oscillatory contractions are associated with calcium (Ca2+)-driven action potentials. We have tested the hypothesis that intracellular Ca2+ stores participate in the generation of norepinephrine-induced oscillatory contractions in tail arteries from SHRSP. Additionally, the role of intracellular Ca2+ stores on TEA-induced contractions were evaluated. Contractile force in strips of tail artery from SHRSP and WKY rats was measured, using standard muscle bath procedures, and the effect of interventions that affect the storage of intracellular Ca2+ on the oscillatory contractions was evaluated. Depletion of intracellular Ca2+ stores, with ryanodine, or inhibition of Ca2+ uptake into the sarcoplasmic reticulum (SR), with thapsigargin and cyclopiazonic acid (CPA), did not inhibit oscillatory contractions induced by norepinephrine in SHRSP vessels. However, these agents inhibited the amplitude of TEA-induced contractions in WKY strips. Bay K 8644 and A23187 inhibited TEA-induced oscillatory contractions in WKY vessels. In SHRSP tail artery Bay K 8644 inhibited both norepinephrine and TEA-induced contractions, while A23187 did not have any effect. The phospholipase C inhibitor, NCDC (3X 10(-5) M), blocked oscillatory activity induced by norepinephrine in SHRSP tail artery and TEA-induced oscillations both in SHRSP and WKY vessels. These observations suggest that Ca2+ release and Ca2+ uptake into intracellular Ca2+ stores are not involved in the contraction-relaxation cycles that characterize norepinephrine-induced oscillatory activity in SHRSP tail artery. Similarly, SR Ca2+ stores may modulate but are not essential for TEA-induced oscillatory contractions.

Topics: 3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; Animals; Arteries; Blood Pressure; Calcimycin; Calcium; Calcium Channel Agonists; Calcium Channels; Calcium Channels, L-Type; Calcium-Transporting ATPases; Carbamates; Enzyme Inhibitors; Female; Hypertension; Indoles; Inositol 1,4,5-Trisphosphate Receptors; Ionophores; Male; Muscle, Smooth, Vascular; Periodicity; Phenylcarbamates; Phosphodiesterase Inhibitors; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Receptors, Cytoplasmic and Nuclear; Ryanodine; Sarcoplasmic Reticulum; Tail; Tetraethylammonium; Thapsigargin; Type C Phospholipases; Vasoconstriction

1. The present study was performed to investigate alterations in membrane characteristics of spontaneously hypertensive rats (SHR) by using an electron paramagnetic resonance (EPR) and spin-labelling methods. 2. Washed erythrocytes from SHR were examined and compared with erythrocytes from age-matched normotensive Wistar-Kyoto (WKY) rats. 3. The values of outer hyperfine splitting (2T' 11) and that of the order parameter (S) obtained from EPR spectra for a spin label agent (5-nitroxide stearate) were significantly higher in the erythrocytes of SHR than in those of WKY rats. 4. When calcium (Ca2+) was loaded to erythrocytes with a Ca2+ ionophore (A 23187), the order parameter (S) of the EPR spectra showed a greater increase in SHR than in WKY rats. Furthermore, the Ca2+ -induced change in the order parameter (S) of SHR was significantly antagonized by pretreatment of the Ca2+ antagonists (verapamil, diltiazem) and a calmodulin antagonist (W-7). 5. The results show that the erythrocyte membranes of SHR tolerated different spin motions from those of normotensive WKY rats in the EPR study, which might be associated with the idea that the membrane fluidity might be lower in SHR. Furthermore, the data suggest that Ca2+ -calmodulin antagonists may ameliorate the Ca2+ -induced changes in membrane functions in hypertension.

Topics: Animals; Calcimycin; Calcium; Calcium Channel Blockers; Calmodulin; Electron Spin Resonance Spectroscopy; Erythrocyte Membrane; Hypertension; Ionophores; Male; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Spin Labels

1. We investigated the effects of hypercholesterolaemia on relaxation responses in thoracic aortas isolated from two different types of hypertensive rats; spontaneously hypertensive rats (SHR) and Dahl salt-sensitive rats (DSR). 2. All rats fed the high cholesterol diet for 8 weeks showed a significant increase in the serum cholesterol level. The high cholesterol diet did not change the blood pressure of SHR, but increased that of hypertensive DSR fed a high-salt diet. 3. In aortas of SHR, the high-cholesterol diet did not change the endothelium-dependent and -independent relaxation induced by acetylcholine (ACh) and sodium nitroprusside (SNP), respectively. 4. In aortas of hypertensive DSR, the high-cholesterol diet notably reduced the ACh-induced relaxations and slightly reduced SNP-induced relaxation. 5. These results suggest that hypercholesterolaemia causes greater impairment of endothelium-dependent relaxation in rat aorta with salt-induced hypertension than genetic hypertension.

Topics: Acetylcholine; Animals; Antihypertensive Agents; Calcimycin; Cholesterol; Cholesterol, Dietary; Diet; Hypercholesterolemia; Hypertension; Ionophores; Male; Muscle Relaxation; Muscle, Smooth, Vascular; Nitroprusside; Rats; Rats, Inbred SHR; Rats, Inbred WKY

The goal of this study was to examine effects of local reductions in intravascular pressure and dP/dt on endothelium-dependent responses of cerebral arterioles in normotensive Wistar-Kyoto rats (WKY) and stroke-prone spontaneously hypertensive rats (SHRSP).. WKY and SHRSP underwent clipping of one carotid artery at 1 month of age. At 6 months of age, responses of pial arterioles were examined in vivo in anesthetized rats. Bilateral craniotomies were performed to expose pial arterioles in the sham-operated and clipped cerebral hemispheres. Pressure (servo-null) was measured in sham-operated and clipped pial arterioles, and arteriolar diameter was measured before and during suffusion with bradykinin, A23187, and nitroprusside.. Carotid clipping normalized pial arteriolar pulse pressure but not mean pressure in SHRSP. Responses of sham-operated pial arterioles to bradykinin and A23187 were less in SHRSP than in WKY. Responses of sham-operated pial arterioles to nitroprusside were greater in SHRSP than in WKY. Carotid clipping in SHRSP normalized responses of pial arterioles to bradykinin but not A23187 and had no effect on responses to nitroprusside.. These findings suggest that elevated intravascular pressure per se may contribute to impairment of endothelium-dependent relaxation to at least some agonists in cerebral arterioles during chronic hypertension. Furthermore, the findings lead us to speculate that arteriolar pulse pressure may play a more important role than mean pressure in development of impaired endothelium dilatation during chronic hypertension.

Topics: Animals; Arterioles; Blood Pressure; Bradykinin; Brain; Calcimycin; Endothelium, Vascular; Hypertension; Nitric Oxide; Nitroprusside; Rats; Rats, Inbred SHR; Rats, Wistar; Vasodilation

Changes of membrane potential of lymphocytes of peripheral blood under the influence of the activation agents: phytohemagglutinin, concanavalin A and Ca(2+)-ionophore A 23187 in 25 patients (men) with hypertensive disease and 8 healthy persons (men) aged 25 to 35 years have been studied. The results obtained testify to the existence of functional disturbances of lymphocytes' membrane and confirmed the wide-spread of the membrane defect in patients with hypertensive disease.

Topics: Adult; Calcimycin; Concanavalin A; Humans; Hypertension; Lymphocyte Activation; Lymphocytes; Male; Membrane Potentials; Phytohemagglutinins

Endothelium-dependent dilatation of cerebral arterioles is impaired during chronic hypertension. The goal of this study was to determine the effects of an angiotensin converting enzyme inhibitor, cilazapril, on endothelium-dependent dilatation in pial arterioles. Four-month-old Wistar-Kyoto (WKY) rats and stroke-prone spontaneously hypertensive rats (SHRSP) received cilazapril in their drinking water (500 mg/L) for 3 to 6 months. Treatment with cilazapril reduced mean arterial pressure in both WKY rats and SHRSP and had no significant effect on baseline diameter of pial arterioles measured with a cranial window. Responses to bradykinin and A23187, but not to nitroglycerin and adenosine, were impaired in SHRSP. Cilazapril did not affect responses to bradykinin (3 x 10(-7) M) and A23187 (10(-5) M) in WKY rats but significantly increased cerebral vasodilatation in response to bradykinin (52 +/- 4% vs 27 +/- 5%) and A23187 (19 +/- 3% vs 8 +/- 3%) in SHRSP. Cilazapril also tended to increase dilator responses to nitroglycerin and adenosine in SHRSP. In another group of SHRSP, treatment with cilazapril for 4 days produced a moderate reduction in blood pressure and increased cerebral vasodilatation in response to bradykinin, A23187, and adenosine. Topical application of the active form of cilazapril (cilazaprilat) for 40 minutes also increased cerebral vasodilatation in response to bradykinin, A23187, and nitroglycerin in SHRSP. The data indicate that an angiotensin converting enzyme inhibitor enhances cerebral vasodilatation in response to endothelium-dependent agonists in SHRSP and may also increase responses to endothelium-independent agonists.

Topics: Animals; Bradykinin; Calcimycin; Cerebrovascular Circulation; Cilazapril; Hypertension; Male; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Vasodilation; Vasodilator Agents

The newly established rat strain TGR(mREN2)27 is a monogenetic model in hypertension research. Microinjecting the mouse Ren-2d renin gene caused it to become a stable part of the genome. The rats are characterized by fulminant hypertension, low plasma active renin, suppressed kidney renin, high plasma inactive renin, and high extrarenal transgene expression, most prominently in the adrenal cortex. Additionally, they exhibit significantly enhanced excretion of corticosteroids. Here we demonstrate that part of the plasma renin and most of the adrenal renin are transgene determined and that the adrenal renin is strongly activated. TGR(mREN2)27 adrenal cells may serve as a new tool to investigate the regulation and processing of Ren-2d-derived renin and its significance in hypertension and steroid metabolism. Adrenal renin in TGR(mREN2)27 is stimulated by 8-bromo-cAMP (8-Br-cAMP), angiotensin II (ANGII), and calcium. 8-Br-cAMP significantly stimulates active renin and prorenin release, as well as Ren-2d mRNA. Interestingly, within 60 min 8-Br-cAMP, ANGII, and calcimycin stimulate active renin, but not prorenin release. This indicates different intracellular pathways. An activated adrenal renin-angiotensin system in TGR (mREN2)27 as well as the lack of negative feedback on renin secretion by ANGII may be of pathophysiological significance in this hypertensive model.

Topics: 8-Bromo Cyclic Adenosine Monophosphate; Adrenal Glands; Angiotensin II; Animals; Animals, Genetically Modified; Calcimycin; Calcium; Cyclic AMP; Disease Models, Animal; Enzyme Precursors; Female; Hypertension; Male; Mice; Rats; Rats, Sprague-Dawley; Renin; RNA, Messenger

We investigated the role of prostanoids in the constrictor effect of calcium ionophore A23187, endothelin-1 and vasopressin in rings of thoracic aorta obtained from normotensive rats and rats with aortic coarctation-induced hypertension. Isometric tension was measured in aortic rings bathed in buffer with and without indomethacin (10 microM), CGS13080 (10 microM) or SQ29548 (1 microM) to inhibit cyclooxygenase and thromboxane synthase and to block TxA2-PGH2 receptors, respectively. Increases in tension elicited by A23187 and vasopressin in aortic rings from hypertensive rats exceeded responses in rings from normotensive rats. A23187-induced contractions were virtually abolished by indomethacin and SQ29548, and slightly attenuated by CGS13080. These agents also attenuated the contractions elicited by endothelin but not by vasopressin. According to these data, a prostanoid(s) agonist for TxA2-PGH2 receptors contributes to the constrictor effect of A23187 in aortic rings of hypertensive rats, and of endothelin in aortic rings of normotensive and hypertensive rats. Moreover, the expression of prostanoid-mediated contractions as it pertains to the aortic response to A23187 is greatly increased in hypertensive rats.

Topics: Animals; Aorta; Blood Pressure; Calcimycin; Endothelins; Endothelium; Hypertension; In Vitro Techniques; Male; Prostaglandins; Rats; Rats, Sprague-Dawley; Vasoconstriction

1. The purpose of the present study was to examine changes in membrane fluidity in hypertension by means of an electron spin resonance (ESR) and a spin labelling methods. 2. Erythrocytes from spontaneously hypertensive rats (SHR) and from patients with essential hypertension were examined and compared with those from age-matched normotensive controls. ESR spectra were obtained for a fatty acid spin label agent (5-nitroxide stearate) in the membranes. The values of outer hyperfine splitting (2T' parallel) and of order parameter (S) of the ESR spectra were significantly higher in erythrocytes from SHR and patients with essential hypertension than in those from normotensive controls. Similar results were obtained in cultured vascular smooth muscle cells of SHR. This finding shows that the membrane fluidity might be lower in SHR and in essential hypertension. 3. When Ca was loaded to erythrocytes with a Ca-ionophore (A23187), the parameters of the ESR spectra showed a greater increase (membrane fluidity was decreased) in SHR and in patients with essential hypertension than that in the normotensive controls. The Ca-induced alterations in membrane fluidity were not definitely observed in secondary hypertension. 4. These results suggest that the lower membrane fluidity might be a genetically determined abnormality of hypertension. The marked reduction of the membrane fluidity by Ca-loading in SHR and in essential hypertension might support the hypothesis that an abnormality of the Ca-handling at cellular levels could affect physical properties of the biomembranes in genetic hypertension.

Topics: Animals; Calcimycin; Calcium; Cells, Cultured; Erythrocytes; Female; Genetic Markers; Humans; Hypertension; Male; Membrane Fluidity; Middle Aged; Muscle, Smooth, Vascular; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Spin Labels

The amounts of tissue factor (TF) expressed by brain microvascular endothelial cells (BMECs) from normotensive Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) were compared after stimulating the cells with different doses of lipopolysaccharide (LPS), thrombin, phorbol myristic acid (PMA), Ca(2+)-ionophore (A23187), or tumor necrosis factor (TNF) and interleukin-1 (IL-1). Treatment of cultured BMECs from WKY and SHR with all of these factors dose-dependently increased their total amount of TF; no substantive differences in the levels of enhanced TF expression were observed between WKY and SHR BMECs. We conclude that stimulated endothelium from rats with hypertension, a major stroke risk factor, is not hyperresponsive with respect to TF expression when compared to normotensive controls.

Topics: Animals; Brain; Calcimycin; Endothelium, Vascular; Hypertension; Interleukin-1; Lipopolysaccharides; Microcirculation; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Tetradecanoylphorbol Acetate; Thrombin; Thromboplastin; Tumor Necrosis Factor-alpha

High contents of Ca2+ was revealed in thrombocytes' intracellular compartments in patients with essential hypertension. In response to different stimuli, large amount of Ca2+ can be released in the platelets of the patients which makes a considerable contribution to generation of the Ca2+ signal and activation of thrombocytes in cardiovascular diseases.

Topics: Blood Platelets; Calcimycin; Calcium; Cell Compartmentation; Cell Membrane; Chlortetracycline; Egtazic Acid; Fluorescent Dyes; Humans; Hypertension; Intracellular Membranes

The present study was designed to clarify the role of calcium in suppressed renin release in DOCA-salt hypertension. Rat glomeruli were isolated by the modified Beierwaltes' sieving method. The glomeruli were superfused with Krebs-Ringer solution. Basal levels of renin release were lower in the DOCA-salt hypertensive rats (1.16 +/- 0.27 ng/ATI/hr/hr/10(4) glomeruli, mean +/- SEM, n = 8) than in the control rats (1.92 +/- 0.18, p less than 0.01, n = 8). Perfusion with a calcium free solution containing EGTA and A23187 stimulated renin release in the DOCA-salt hypertensive and control rats. The maximum levels of renin release during the perfusion in DOCA-salt hypertensive rats (1.79 +/- 0.17, n = 8) were lower than those in control rats (10.60 +/- 1.85, p less than 0.01, n = 8). These results suggest that high levels of intracellular calcium might not contribute to the suppression of renin release in DOCA-salt hypertension.

Topics: Animals; Calcimycin; Calcium; Desoxycorticosterone; Egtazic Acid; Hypertension; In Vitro Techniques; Kidney Glomerulus; Male; Perfusion; Rats; Rats, Inbred Strains; Renin; Sodium Chloride

Topics: Animals; Calcimycin; Calcium; Cytoskeleton; Erythrocytes; Hypertension; Lanthanum; Male; Nucleotides; Rats; Rats, Inbred SHR; Rats, Inbred WKY

1. The sensitivity of the kidney to endothelium-derived-relaxing-factor-mediated vasodilatation has been investigated in the spontaneously hypertensive rat and the Wistar-Kyoto normotensive rat using an isolated perfused rat kidney model. 2. No difference in the slope, ED50 or maximum of the concentration-response curves for the endothelial-dependent vasodilators A23187, a calcium ionophore, and acetylcholine could be demonstrated between kidneys obtained from the spontaneously hypertensive and the Wistar-Kyoto normotensive rats. 3. No difference in the slope or the ED50 of the concentration-response curve for the endothelial-independent vasodilators, atrial natriuretic factor and sodium nitroprusside, could be demonstrated between kidneys obtained from the spontaneously hypertensive and the Wistar-Kyoto normotensive rats. However, in the spontaneously hypertensive rats, the maximum vasodilator response to atrial natriuretic factor, but not to sodium nitroprusside, was increased. 4. The perfused kidney from the spontaneously hypertensive rat also showed an increase in the maximum but not in the slope or ED50 of the concentration-response curve for vasoconstriction induced by the alpha 1-adrenoceptor agonist methoxamine. 5. The involvement of endothelium-derived relaxing factor in mediating the renal vasodilator response to A23187 and acetylcholine was confirmed in experiments performed in perfused kidneys obtained from normotensive Wistar rats. 6. It is concluded that the sensitivity of the kidney to endothelium-derived-relaxing-factor-mediated vasodilatation is not modified in the spontaneously hypertensive rat. This does not, however, exclude a role for the synthesis of endothelium-derived relaxing factor in the maintenance of blood pressure in the spontaneously hypertensive rat.

Topics: Acetylcholine; Animals; Atrial Natriuretic Factor; Calcimycin; Dose-Response Relationship, Drug; Hypertension; Kidney; Male; Nitric Oxide; Nitroprusside; Perfusion; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Vasodilation

Acetylcholine produces less dilatation of pial arterioles in stroke-prone spontaneously hypertensive rats (SHRSP) than in normotensive (WKY) rats. Responses of cerebral vessels to acetylcholine and bradykinin appear to involve different mechanisms. Our first goal was to determine whether responses of pial arterioles to bradykinin are impaired in SHRSP. Diameter of pial arterioles (20-60 microns) was measured using intravital microscopy in WKY rats and SHRSP (9-12 months old). Superfusion of bradykinin (3 x 10(-7) M) dilated pial arterioles by 35 +/- 6% (mean +/- SEM) in WKY rats, but only 21 +/- 3% in SHRSP (p less than 0.05 versus WKY rats). Both nitric oxide (5 x 10(-7) M) and nitroglycerin (10(-5) M) produced similar vasodilatation in WKY rats and SHRSP. Our second goal was to determine whether alteration of postreceptor mechanisms contributes to impairment of endothelium-dependent cerebral vasodilatation in SHRSP. Calcium ionophore A23187 (10(-5) M) produced more vasodilatation in WKY rats than in SHRSP (32 +/- 8% versus 9 +/- 4%, p less than 0.05). Responses to A23187 (10(-5) M) were inhibited by indomethacin (46 +/- 13% versus 15 +/- 5%, p less than 0.05) in WKY rats, whereas responses to A23187 (10(-6) M) were potentiated modestly by indomethacin (-3 +/- 2% versus 4 +/- 2%, p less than 0.05) in SHRSP.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Animals; Arterioles; Blood Pressure; Bradykinin; Calcimycin; Cerebrovascular Circulation; Cerebrovascular Disorders; Chronic Disease; Disease Susceptibility; Endothelium, Vascular; Hypertension; Male; Nitroglycerin; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Vasodilation

These experiments compared potential-operated calcium channel function in smooth muscle from stroke-prone spontaneously hypertensive rats (SHRSP) and normotensive Wistar-Kyoto rats (WKY). Carotid artery strips from adult male SHRSP and WKY rats were suspended in tissue baths for isometric force recording. Contractile force was expressed as percent of response to 100 mmol/l KCl. Vascular strips from SHRSP were more sensitive to KCl (ED50 = 25 mmol/l) compared to strips from WKY rats (ED50 = 37 mmol/l). The calcium channel agonist Bay K 8644 (2.8 x 10(-10) to 2.8 x 10(-7) mol/l) produced tonic contractions in carotid artery strips from SHRSP (34% of the contractile response to 100 mmol/l KCl) but not in those from WKY rats. Incubation of vascular strips in 1.8 or 6 x 10(-10) mmols/l norepinephrine did not alter the maximal contractile response to Bay K 8644 in either strain of rats. In 12 mmol/l KCl, the maximal contractile response to Bay K 8644 was increased in both SHRSP (71%) and WKY rats (25%). In 18 mmol/l KCl, maximal contractile responses to Bay K 8644 in the two strains were similar (SHRSP = 73%, WKY = 76%). Removal of the endothelium did not significantly affect contractile responses to Bay K 8644 in either strain of rats. There were no differences in contractile responses to the calcium ionophore A23187 or in nifedipine-induced relaxation of potassium-activated vessels between carotid arteries from SHRSP and WKY rats. In summary, these results suggest that a difference in voltage-operated calcium channel function may underlie the increased sensitivity of SHRSP vascular smooth muscle to depolarizing stimuli.

Topics: 3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; Animals; Calcimycin; Carotid Arteries; Endothelium, Vascular; Hemodynamics; Hypertension; In Vitro Techniques; Isometric Contraction; Male; Muscle Contraction; Muscle, Smooth, Vascular; Nifedipine; Norepinephrine; Potassium Chloride; Rats; Rats, Inbred SHR; Rats, Inbred WKY

The capacity of cultured renal medullary interstitial cells derived from Dahl salt-sensitive and salt-resistant rats to synthesize prostaglandin E2 (PGE2) was compared. Basal and arginine vasopressin (AVP)-induced PGE2 production by interstitial cells from salt-resistant rats was fourfold to fivefold higher than corresponding values of those from the salt-sensitive rats. Similarly, basal and AVP-responsive release of [3H]arachidonate were twofold higher by interstitial cells from salt-resistant compared with salt-sensitive rats. Differences in PGE2 production were abolished by the calcium inophore A23187 or the addition of exogenous arachidonate. The latter findings suggested a role for altered availability of endogenous arachidonate, possibly mediated by reduced calcium-responsive lipase activity. Basal and AVP-induced increases in cytosolic free calcium concentration, assessed by the aequorin method, were significantly lower in interstitial cells from salt-sensitive versus salt-resistant rats, further supporting a possible role for altered cellular calcium homeostasis. Studies of the potential contribution of various phospholipases and of triglyceride lipase to the release of arachidonate for PGE2 synthesis in interstitial cells implicated phospholipase A2 activity as a major pathway. When assessed in vitro in cell cytosolic fractions at identical calcium concentration, phospholipase A2 activity was lower in interstitial cells from salt-sensitive versus salt-resistant rats. Thus, both reduced cytosolic free calcium and phospholipase A2 activity of interstitial cells from salt-sensitive rats may contribute to the diminished capacity of these cells to liberate endogenous arachidonate for PGE2 synthesis.

Topics: Animals; Arachidonic Acid; Arachidonic Acids; Arginine Vasopressin; Calcimycin; Calcium; Cytosol; Dinoprostone; Disease Susceptibility; Extracellular Space; Hypertension; Kidney Medulla; Male; Osmolar Concentration; Rats; Rats, Inbred Strains; Sodium Chloride

We investigated the vascular responsiveness to vasoactive agents and the inhibition by H-7 (1-(5-isoquinoline-sulfonyl)-2-methylpiperazine), which inhibits cyclic nucleotide-dependent protein kinases and protein kinase C(PKC) equally potently in helically cut strips of thoracic aortas from spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY). The susceptibility of norepinephrine (NE)- and angiotensin II (Ang II)-induced contractions to H-7 was significantly higher in the aortas from SHR than in those from WKY. H-7 decreased the contractile responses to KCl to a similar extent in both strains without affecting the high K(+)-stimulated Ca2+ influx. H-7 produced a shift to the right of the dose-response curve for the PKC activator, 12-o-tetradecanoylphorbol-13-acetate (TPA) in the case of SHR aortas, while no such shift was noted in tissues from WKY. Functional alterations in the PKC branch of the Ca2+ messenger system in vascular smooth muscle may play an important role in SHR during the sustained contraction.

Topics: 1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; Angiotensin II; Animals; Aorta, Thoracic; Calcimycin; Calcium; Dinoprost; Hypertension; In Vitro Techniques; Isoquinolines; Lanthanum; Male; Muscle Contraction; Muscle, Smooth, Vascular; Norepinephrine; Phorbol Esters; Piperazines; Potassium Chloride; Protein Kinase Inhibitors; Rats; Rats, Inbred SHR; Rats, Inbred WKY

The effects of LF 2.0254, a new 1,4-dihydropyridine derivative, were studied in rabbit aorta stimulated by various contractile agents and in isolated guinea pig atria. LF 2.0254 inhibited in a time-dependent fashion K(+)- and CA2(+)-induced contractions of rabbit aorta with respective IC50 of 2.7 nM and 1.7 nM. An action of LF 2.0254 at the voltage operated calcium channel was consistent with the finding that LF 2.0254 antagonized 45Ca2(+)-uptake induced by depolarisation of smooth muscle, and since contractile responses evoked by (-) norepinephrine and the calcium ionophore A23187 were insensitive to the drug. In isolated paced left atria and spontaneously beating right atria of guinea pig, LF 2.0254 added for 60 min at 1 microM only slightly decreased the contractile force and beating rate. In anesthetized open-thorax dogs, LF 2.0254 (1 to 100 micrograms/kg, iv) dose-dependently lowered systemic blood pressure and increased cardiac output with a slower onset of action than nifedipine. LF 2.0254 and nifedipine decreased total peripheral, coronary, femoral and vertebral resistance. In marked contrast to nifedipine, LF 2.0254 induced only a slight decrease in left ventricular dP/dt. In conscious hypertensive dogs LF 2.0254 (0.1 and 0.3 mg/kg per os) decreased blood pressure and concomitantly increased heart rate and plasma renin activity. It is concluded that LF 2.0254 differ markedly from nifedipine in its more gradual onset of action and greater selectivity for the vasculature with respect to the myocardium.

Topics: Anesthesia; Animals; Calcimycin; Calcium Channel Blockers; Calcium Chloride; Calcium Radioisotopes; Dihydropyridines; Dogs; Female; Guinea Pigs; Heart; Hemodynamics; Hypertension; In Vitro Techniques; Male; Muscle Contraction; Muscle, Smooth, Vascular; Nifedipine; Norepinephrine; Potassium; Rabbits; Rats

In the present study, age- and calcium-related changes in the membrane fluidity of erythrocytes were examined in patients with essential hypertension by use of electron spin resonance method (ESR). The erythrocytes were obtained from patients with essential hypertension. We examined the ESR spectra for a fatty acid spin label agent (5-nitroxy stearate) incorporated into the erythrocyte membranes. The values of outer hyperfine splitting and order parameter (S) were significantly higher in subjects with essential hypertension than in the normotensive subjects. This finding indicates that the membrane fluidity of erythrocytes was lower in essential hypertension. Calcium-loading of erythrocytes with the Ca-ionophore A23187 decreased the membrane fluidity (S value was increased) more strongly in essential hypertension than in the normotensive subjects. Furthermore, this Ca-induced change in membrane fluidity was significantly correlated with age in essential hypertension. These results demonstrate that the membrane fluidity of erythrocytes is markedly decreased by calcium, especially in essential hypertension in older patients. This suggests an increased calcium-sensitivity of cell membranes in the aged hypertensive patient.

Topics: Aging; Calcimycin; Calcium; Electron Spin Resonance Spectroscopy; Erythrocyte Membrane; Humans; Hypertension; Membrane Fluidity; Middle Aged

The mechanism of platelet dysfunctions in stroke-prone spontaneously hypertensive rats (SHRSP) was investigated. Platelet aggregation was inversely correlated with blood pressure or heart weight/body weight ratios in various strains of spontaneously hypertensive rats (SHR), indicating genetic defects. Thrombin-induced 47 kDa protein phosphorylation was markedly reduced in platelets of SHRSP compared with that in Wistar-Kyoto (WKY) rat platelets, accompanying reduced aggregation and secretion, but in 20 kDa protein phosphorylation was unchanged. Ca2+ ionophore A23187-induced responses were also significantly decreased in SHRSP, and the degrees of the changes were greater than those by thrombin. However, 12-O-tetradecanoylphorbol 13-acetate-induced responses in SHRSP were similar to those in WKY rats, suggesting that protein kinase C activity and its substrate were normally present in SHRSP platelets. Phosphatidylinositol content in platelets of SHRSP was 20% less than that in WKY rat platelets, but the contents of other phospholipids, including phosphatidylinositol-4-monophosphate and phosphatidylinositol-4,5-bisphosphates, were unaltered. Thrombin-induced formation of diacylglycerols and phosphatidic acid did not differ from each other at the low concentrations. In the absence of Ca2+, thrombin-induced responses occurred to a similar degree in both platelets, whereas the enhancements by Ca2+ were much greater in WKY rats than in SHRSP. These results suggested that defective Ca2+ functions in receptor-mediated activation of protein kinase C and postkinase-mediated events appear to be an underlying mechanism for the hypofunctions in SHRSP platelets.

Topics: Animals; Blood Platelets; Blood Pressure; Blood Proteins; Calcimycin; Calcium; Cerebrovascular Disorders; Diglycerides; Disease Susceptibility; Hypertension; Phosphatidic Acids; Phospholipids; Phosphorylation; Platelet Aggregation; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Tetradecanoylphorbol Acetate; Thrombin

The correlation between the alterations of free intracellular calcium concentrations and the essential arterial hypertension has been largely investigated. Calmodulin, a cytoplasmic protein with low molecular weight, is one of the factors known to be able to affect the activity of calcium-dependent enzymes. The authors have investigated the effect of calcium and calmodulin on the plasmatic membrane of intact erythrocytes in a group of patients with essential arterial hypertension. To this purpose, the ionophor A23187, propranolol at low concentrations and a few calcium channel blocking drugs, alone or associated with calmodulin have been used. The results demonstrate that calmodulin, capable of blocking calcium outside the cell, can exert its effect only when propranolol is also present in the erythrocytes of normotensive but not in the hypertensive patients. The authors discuss some pathogenetic hypotheses.

Topics: Adult; Calcimycin; Calcium; Calcium Channel Blockers; Calmodulin; Erythrocytes; Female; Humans; Hypertension; In Vitro Techniques; Male; Potassium; Propranolol

Isolated aortas from hypertensive rats have a decreased relaxation response to acetylcholine chloride (ACh), the calcium ionophore A23187, and sodium nitroprusside (SNP). Since the vascular relaxation responses to these vasodilators may be a result of increases in guanosine 3',5'-cyclic monophosphate (cGMP), we measured the cGMP response to these agents in isolated aortas from normotensive rats and rats with either mineralocorticoid-induced hypertension (DOCA), renovascular hypertension (1K1C), or coarctation-induced hypertension (Coarc). The aortas from the hypertensive rats had decreased basal levels of cGMP and attenuated increases in cGMP in response to ACh and A23187. Rises in cGMP in response to SNP were also attenuated in aortas from the hypertensive rats, even at concentrations that induced maximum relaxation of blood vessels from normotensive and hypertensive rats. The relaxation responses to atrial natriuretic factor (ANF) and the cGMP generated in isolated aortas by ANF were attenuated in hypertension. Removal of the endothelium markedly attenuated cGMP generation in response to ANF in vessels from normotensive and Coarc rats, but the relaxation responses to ANF were unaltered in vessels after the removal of the endothelium. The reversal of experimentally induced hypertension was associated with increases in cGMP levels following exposure of the isolated vessels to ACh. Also, vessels treated with methylene blue relaxed in response to SNP despite inhibition of cGMP accumulation. The decreased relaxation response to endothelium-dependent vasodilators is accompanied by decreases in cGMP accumulation; the decreased vascular cGMP content in response to endothelium-dependent vasodilators is not due to increases in phosphodiesterase activity of vascular smooth muscle; and SNP may relax blood vessels through "cGMP-dependent" and "cGMP-independent" mechanisms.

Topics: Animals; Aortic Coarctation; Atrial Natriuretic Factor; Biological Products; Calcimycin; Cyclic GMP; Desoxycorticosterone; Hypertension; Male; Nitric Oxide; Nitroprusside; Rats; Rats, Inbred Strains; Vasodilation

Renal papillary collecting tubule (RPCT) hormone responsiveness was compared between cultured RPCT cells from spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY). Unstimulated cells from 4-week-old SHR produced less prostaglandin E2 (PGE2) and cyclic (c)AMP than comparable cells from WKY, while cells from both stains synthesized similar amounts of PGE2 after stimulation with arachidonate, A23187 or bradykinin and similar amounts of cAMP after stimulation with vasopressin or PGE2. There was no difference in basal or stimulated levels of cyclic (c)GMP between the strains. In RPCT cells from 16-week-old rats, basal levels of cAMP, cGMP and PGE2 were significantly lower than those from 4-week-old rats, but they did not differ between the strains. These results suggest that RPCT cells of SHR and WKY at the post-weaning period may differ in the metabolism of PGE2 and cAMP. This difference may be attributed to the possible defect in arachidonate availability in SHR.

Topics: Age Factors; Animals; Arachidonic Acid; Arachidonic Acids; Arginine Vasopressin; Calcimycin; Cells, Cultured; Cyclic AMP; Dinoprostone; Hypertension; Kidney Medulla; Kidney Tubules; Kidney Tubules, Collecting; Nitroprusside; Rats; Rats, Inbred SHR; Rats, Inbred Strains

Free intracellular magnesium in red blood cells (RBC) of 9 normotensives and 7 essential hypertensives was estimated from the amount of magnesium released by an incubation with the ionophore A 23187 (8 microM). In hypertensives, Mg released to the suspension medium was 0.42 +/- 0.10 mmol/l, thus being significantly lower than in normotensives (0.52 +/- 0.09 mmol/l; p less than 0.05). Total RBC Mg and serum Mg were not different in both groups. The chloride distribution ratio between the extracellular and intracellular concentrations was insignificantly increased in hypertensives, thus indicating a depressed intracellular chloride concentration as reported earlier. This ratio is essential for the calculation of the free intracellular Mg from equilibrated extracellular Mg. Taking the latter finding into account, no significant depression of free intracellular Mg can be detected in RBC of hypertensives in this study.

Topics: Calcimycin; Erythrocytes; Female; Hematocrit; Humans; Hypertension; Magnesium; Male; Middle Aged

Decreased 45calcium uptake was observed in red cells of 20 patients with essential hypertension. Equilibration of extracellular 45calcium with intracellular calcium was not achieved within 60 min in red cells of either hypertensive patients or control subjects. By introducing the ionophore A23187, equilibrium conditions were attained for red cells of both categories of individuals. Still the discrepancy in 45calcium uptake was preserved between them. These results support the view that red cells of hypertensive patients have an altered membrane permeability to calcium, possibly reflecting also a greater exchangeable pool of cytosolic free calcium.

Topics: Adult; Calcimycin; Calcium; Erythrocytes; Extracellular Space; Humans; Hypertension; Male; Middle Aged

The kinetic parameters of the Ca2+ pump were assessed in red blood cells of essential hypertensive subjects as compared to their respective controls. Uphill Ca2+ efflux was investigated in Ca2+ -saturated intact red blood cells using a new method recently developed for human red cells (Dagher,G. and Lew, V. J. Physiol. (London), in the press). 45Ca-equilibrated cells were obtained using ionophore A23187 and Ca2+ efflux was assessed after addition of excess CoCl2 which totally inhibits Ca2+ influx and thus exposes uphill Ca2+ extrusion by the pump. The results comprise methodological aspects of the use of this technique in rat red blood cells. The determination of the maximal velocity and the Ca2+ concentration for half-maximal stimulation (KCa 0.5) did not reveal any alteration in essential hypertensives and spontaneously hypertensive rats as compared to their controls.

Topics: Adult; Aged; Animals; Calcimycin; Calcium; Calcium Radioisotopes; Cobalt; Erythrocytes; Humans; Hypertension; Ion Channels; Kinetics; Male; Membrane Potentials; Middle Aged; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Vanadates

Responsiveness to endothelium-dependent (acetylcholine and A23187) and endothelium-independent (nitroprusside and 8-bromo cyclic guanosine 3',5'-monophosphate [cGMP]) vasodilators was examined in two vascular preparations from hypertensive and normotensive mice. CBA Agouti mice were made hypertensive by exposure to social stress in a complex population cage. After 2 months, the hindquarter vascular bed was pump-perfused at a constant flow with plasma substitute to evaluate changes in perfusion pressure, and helical strips of aorta were suspended in muscle baths for measurement of isometric force generation. Tissues were treated with methoxamine to induce contractile tone. Threshold dilator responses to acetylcholine were elicited at a significantly lower dose in the hindquarters of hypertensive mice than in those from normotensive mice, indicating increased vasodilator sensitivity. In contrast, vasodilator responsiveness to nitroprusside in hindquarters of hypertensive mice did not differ from that in hindquarters of normotensive mice. Aortas from hypertensive mice were more sensitive (lower ED50) to the relaxant effects of acetylcholine and A23187 than those from normotensive mice. The relaxant effects of nitroprusside and 8-bromo cGMP on aortas from hypertensive mice were not significantly different from those in normotensive aortas. Aortic strips that had been rubbed on the lumen surface with a wooden stick did not relax to acetylcholine or A23187. In aortas that were not initially contracted with methoxamine, acetylcholine and A23187 caused small contractions from baseline. The magnitude of these contractile responses were potentiated after removal of the endothelium, and the potentiation was greater in aortas from hypertensive mice. These results demonstrate an increased responsiveness to endothelium-dependent vasodilators in this psychosocial model of hypertension.

Topics: Acetylcholine; Animals; Aorta; Calcimycin; Crowding; Cyclic GMP; Hypertension; Male; Methoxamine; Mice; Nitric Oxide; Nitroprusside; Vasodilation; Vasodilator Agents

The purpose of the present study was to investigate erythrocyte membrane abnormalities in hypertension by means of an electron spin resonance and spin-label technique. The erythrocytes from spontaneously hypertensive rats (SHR) and humans with untreated essential hypertension were examined and compared with their normotensive counterparts, and electron spin resonance spectra were obtained for a fatty spin-label agent (5-nitroxy stearate) incorporated into the erythrocyte membranes. The value of outer hyperfine splitting (2T' parallel) was significantly higher in erythrocytes of SHR and humans with essential hypertension than in erythrocytes of normotensive controls (at 37 degrees C: SHR, 56.14 +/- 0.51 gauss [G], n = 8; Wistar-Kyoto rats, 52.22 +/- 0.86 G, n = 4, p less than 0.01; humans with essential hypertension, 56.94 +/- 0.27 G, n = 11; normotensive subjects, 55.44 +/- 0.36 G, n = 8, p less than 0.01). The order parameter (S) was also increased in the hypertensive rats and humans compared to their respective normotensive controls. When calcium was loaded to erythrocytes with calcium ionophore A23187 (0.9 microM) and CaCl2 (1.0 mM), the parameters of the spectra were increased. These changes were more prominent in the hypertensive groups than in the normotensive controls. These results revealed that the erythrocyte membranes of the hypertensive subjects tolerated different spin motions than those of the normotensive controls in the electron spin resonance study and that membrane fluidity might be decreased in hypertension. Additionally, calcium loading to erythrocytes caused the reduction of membrane fluidity. Therefore, it is suggested that an abnormality of calcium handling at the cellular level might affect physical properties of the biomembranes in hypertension.

Topics: Adult; Animals; Calcimycin; Calcium; Electron Spin Resonance Spectroscopy; Erythrocytes; Fatty Acids; Female; Humans; Hypertension; Male; Middle Aged; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Spin Labels

In hemolysates of red cells from hypertensive patients the proteolytic activity of calpain is expressed at a rate approximately three fold higher than in red cells of normotensive subjects. Susceptibility to lysis upon exposure to ionophore A23187 and calcium, conditions that increase intracellular calpain activity, is also significantly enhanced in erythrocytes of hypertensive patients. In inside-out vesicles prepared from erythrocytes of these patients band 3 region undergoes a high extent of phosphorylation which is 1.5 fold higher than that occurring in control red cells from normotensive subjects. This increased phosphorylation can be reproduced in inside-out vesicles from erythrocytes of normal subjects following pretreatment with calpain. Taken together, these results suggest that the presence in erythrocytes of hypertensive subjects of an unregulated calpain dependent proteolytic activity may affect the structure of plasma membranes and determine an increased phosphorylation of intrinsic membrane proteins.

Topics: Anion Exchange Protein 1, Erythrocyte; Calcimycin; Calcium; Calpain; Erythrocyte Membrane; Hemolysis; Humans; Hypertension; Kinetics; Phosphorylation; Reference Values

Rabbits were rendered hypertensive by suprarenal coarctation of the abdominal aorta. Seven days later, endothelium-dependent and endothelium-independent vascular relaxations were examined in vascular rings taken from hypertensive (thoracic aorta, carotid artery) and normotensive (abdominal aorta) regions. Relaxation of phenylephrine-contracted rings in response to endothelium-dependent agonists (acetylcholine, A23187) was impaired, compared with that in sham-operated and intact controls, in regions exposed to the elevated blood pressure (i.e., above the coarctation). Responses to acetylcholine and A23187 in the abdominal aorta, below the coarctation, were not altered. The diminished endothelium-dependent responses in the thoracic aorta were not affected by pretreatment with the cyclooxygenase inhibitor indomethacin. In contrast to acetylcholine and A23187, responses to the endothelium-independent agonist nitroprusside were not attenuated in vessels from hypertensive regions, indicating that the defect occurred in the endothelium. The EC50 for acetylcholine-induced relaxations of thoracic aorta correlated significantly with mean arterial pressure above the coarctation, indicating that the extent to which endothelium-dependent relaxation is impaired is in proportion to the degree of blood pressure elevation. This study suggests that the diminished relaxations by endothelium-dependent agonists is a local response to the elevation of blood pressure and is not due to a circulating factor.

Topics: Acetylcholine; Animals; Aorta, Abdominal; Aorta, Thoracic; Aortic Coarctation; Calcimycin; Carotid Arteries; Endothelium; Hypertension; Indomethacin; Male; Muscle Contraction; Muscle Relaxation; Muscle, Smooth, Vascular; Nitroprusside; Phenylephrine; Rabbits

We investigated endothelium-dependent relaxation in rat aortae, using three models of experimental hypertension: deoxycorticosterone and salt; one-kidney, one clip renovascular hypertension; and coarctation. Isolated aortae were contracted with phenylephrine, and relaxation was subsequently induced with acetylcholine or calcium ionophore A23187. Blood vessels denuded of endothelium did not relax in response to acetylcholine or A23187. Blood vessels from animals with high blood pressure had decreased relaxation responses to acetylcholine and A23187, and also to the endothelium-independent vasodilator sodium nitroprusside. Unlike acetylcholine and A23187, however, nitroprusside completely relaxed the blood vessels from the hypertensive animals, though the sensitivity to nitroprusside was much lower in these vessels. Subsequent reversal of hypertension caused a return of endothelium-dependent relaxation. Loss of endothelium-dependent relaxation occurs readily in the aortae with the development of hypertension; this phenomenon appears to be related to elevated pressure.

Topics: Acetylcholine; Animals; Aorta; Arachidonic Acid; Arachidonic Acids; Calcimycin; Desoxycorticosterone; Hypertension; In Vitro Techniques; Indomethacin; Male; Nitric Oxide; Rats; Rats, Inbred Strains; Vasodilation; Vasodilator Agents

The functional significance of the Na+,K+-ATPase activity in defining the sensitivity of vascular smooth muscle response to pressor stimuli was studied in guinea pig aortic strips. Subthreshold doses of ouabain (10(-8), 10(-7), 10(-6)M), potentiated the norepinephrine- and angiotensin II-induced contractile responses, dose-dependently. Furthermore, in the presence of subthreshold dose of ouabain (10(-6)M), tension developments were observed with subthreshold doses of norepinephrine and angiotensin II. The mechanism by which subthreshold dose of ouabain potentiated the norepinephrine-induced contractile response was revealed to involve the enhancement both of sensitivity and contractile activity. Ouabain (10(-6)M) potentiated the norepinephrine- and A23187-induced contractile responses, even in the presence of verapamil. These facts indicate that suppression of the vascular Na+,K+-ATPase activity could favor the development of hypertension through potentiating contractile responses to various stimuli and that the potentiation could be a reflection, at least partly, of the decrease in Ca2+-efflux.

Topics: Angiotensin II; Animals; Aorta, Thoracic; Calcimycin; Calcium; Guinea Pigs; Hypertension; In Vitro Techniques; Male; Muscle, Smooth, Vascular; Norepinephrine; Ouabain; Sodium-Potassium-Exchanging ATPase; Vasoconstriction

The relaxation response to endothelium-dependent (acetylcholine and the calcium ionophore A23187) and independent (sodium nitroprusside) vasodilators was examined in isolated aortic ring segments from age-matched genetically hypertensive (GH) and normotensive (N) rats (New Zealand strain). Tissues were initially contracted with methoxamine to achieve similar levels of contractile force. The IC20, IC40 and IC50 values for acetylcholine, A23187 and sodium nitroprusside were shifted significantly to the right (P less than 0.05) in aortic rings from GH rats compared to the corresponding values in N rats. The maximal relaxation achieved by acetylcholine and A23187 was significantly depressed in aortas from GH rats (P less than 0.05). Sodium nitroprusside elicited the maximal relaxation in both groups of tissues. These results demonstrate that there exists a generalized defect in the relaxant ability of vascular smooth muscle from GH rats. In addition, our findings suggest that this defect is coupled with a decreased responsiveness to endothelium-dependent vasodilators in this particular animal model of hypertension.

Topics: Acetylcholine; Animals; Aorta; Calcimycin; Dose-Response Relationship, Drug; Endothelium; Hypertension; Methoxamine; Muscle Contraction; Nitroprusside; Rats; Rats, Inbred SHR; Vasodilation

Platelet aggregation, plasmatic membrane potential and sodium and calcium uptake were investigated in spontaneously hypertensive rats (SHR). The sensitivity of SHR's platelets to effects of all aggregational agents examined (ADP, collagen, ADP + noradrenaline) was enhanced. Ca-ionophore A 23187 caused complete SHR platelet aggregation when Ca2+ concentration in the incubation medium was 20-30% below the level of normotensive control specimens. The membrane potential of SHR platelets was reduced by 8-12 mV, which may be attributed to increased content of metabolizing sodium as well as a higher rate of its transmembrane exchange. A higher rate of Ca2+ uptake by SHR platelets may be related to partial depolarization of the membrane and the cation's diffusion along potential-dependent Ca-channels.

Topics: Adenosine Diphosphate; Animals; Biological Transport; Calcimycin; Calcium; Collagen; Hypertension; Ion Channels; Male; Membrane Potentials; Norepinephrine; Platelet Aggregation; Rats; Rats, Inbred Strains; Sodium

Calcium binding was significantly reduced, and lipid microviscosity increased, in platelet membranes and erythrocyte shadows of spontaneously hypertensive rats (SHR). Their platelet sensitivity to calcium was already increased at the prehypertensive stage, and the rate of A23187-induced platelet aggregation was increased significantly by 24 weeks of life. The demonstrated biochemical properties of SHR's platelet membranes can account for their increased aggregative capacity and may be important in the pathogenesis of arterial hypertension.

Topics: Animals; Binding Sites; Blood Platelets; Calcimycin; Calcium; Cell Membrane; Erythrocyte Membrane; Hypertension; Membrane Lipids; Platelet Aggregation; Rats

A large number (about 4--5 nmol/mg of protein) of high-affinity (apparent dissociation constant at 37 degrees C: KD37 degrees C = 5 x 10(-8) M) calcium binding sites was characterized in synaptosomal membrane fractions enriched in plasma membranes that were isolated from rat brain. These sites were studied simultaneously in membranes from spontaneously hypertensive young rats (SHR) and their normotensive controls. No difference was observed between whole synaptosomes from these two substrains. However, plasma membrane-enriched fractions from SHR exhibited a reduced calcium binding capacity without a significant change in affinity. This decrease which averaged 15--20% was not due to any variation in the accessibility of calcium to its binding sites, as similar results were obtained in the presence of the calcium ionophore A23187. The reduction found in calcium binding is very similar to that previously described in erythrocyte membranes. It is envisaged that such an abnormality at nerve endings might play a role in the pathogenesis of genetic hypertension.

Topics: Acetylcholinesterase; Aging; Animals; Calcimycin; Calcium; Hypertension; Male; Rats; Rats, Inbred Strains; Synaptic Membranes; Synaptosomes; Time Factors

Topics: Animals; Blood Platelets; Calcimycin; Cyclic AMP; Cyclic GMP; Disease Models, Animal; Epinephrine; Humans; Hypertension; Platelet Aggregation; Prostaglandins E; Serotonin; Species Specificity

Topics: Adenylyl Cyclases; Age Factors; Animals; Blood Platelets; Blood Vessels; Calcimycin; Cyclic AMP; Cyclic GMP; Epinephrine; Hypertension; Muscle, Smooth; Nucleotides, Cyclic; Platelet Aggregation; Prostaglandins E; Rats; Rats, Inbred Strains