bq-123 and Hypertension

Topics: Animals; Antihypertensive Agents; Blood Pressure; Drug Design; Endothelin Receptor Antagonists; Endothelin-1; Humans; Hypertension; Mice; Mice, Knockout; Muscle Contraction; Muscle, Smooth, Vascular; Peptides, Cyclic; Pyrimidines; Receptors, Endothelin; Sulfonamides

Topics: Animals; Endothelins; Humans; Hypertension; Mice; Peptides, Cyclic; Vasoconstriction

Endothelin family peptides are now known to exert diverse biological effects on a wide variety of tissues and cell types through at least two subtypes of receptors. In vascular systems, both ETA and ETB endothelin receptors present in vascular smooth muscle mediate the vasoconstrictor and mitogenic activities of the peptides, while ETB receptors in the endothelium mediate the vasodilator and antiplatelet activities. Endothelins also affect hormone secretion from a variety of endocrine organs including anterior and posterior pituitary, atria and adrenals. Endothelins activate the Ca(2+)-messenger system which involves both calmodulin and protein kinase C to exert their biological activities in almost all cell types examined, and appear to work in a paracrine and autocrine fashion. However, physiological and pathophysiological roles of endothelins are still incompletely understood and further studies are clearly required for elucidation of biological significance of this peptide family.

Topics: Animals; Blood Vessels; Calcium; Endocrine Glands; Endothelins; Endothelium, Vascular; Hemodynamics; Hormones; Humans; Hypertension; Ischemic Attack, Transient; Muscle, Smooth, Vascular; Neuropeptides; Peptides, Cyclic; Rats; Rats, Inbred SHR; Receptors, Endothelin; Second Messenger Systems

Topics: Amino Acid Sequence; Animals; Endothelin Receptor Antagonists; Endothelins; Hypertension; Ischemic Attack, Transient; Molecular Sequence Data; Peptides, Cyclic; Receptors, Endothelin; Streptomyces; Vasoconstriction

This study tested the hypothesis that pioglitazone reduces endothelin-1 activity in the forearm vasculature in non-diabetic patients with hypertension or hypercholesterolemia and variable degrees of insulin resistance.. We conducted a single center, randomized, double-blind, placebo controlled, cross-over trial in 80 patients with either hypertension or hypercholesterolemia and further classified as insulin-sensitive or insulin-resistant based on a published insulin sensitivity index. Participants received pioglitazone 45 mg daily or matching placebo for eight weeks. The main endpoint was the change in forearm vascular endothelin-1 activity, as assessed by intra-arterial infusion of the endothelin type A receptor blocker BQ-123, measured at the end of each 8-week treatment period.. Pioglitazone lowered plasma insulin (P < 0.001), improved insulin sensitivity (P < 0.001), increased HDL (P < 0.001), and reduced triglycerides (P = 0.003), free fatty acids (P = 0.005), and C-reactive protein (P = 0.001). However, pioglitazone did not affect the vasodilator response to BQ-123 in the whole group (P = 0.618) and in the diagnosis or insulin sensitivity subgroups. Hence, in non-diabetic patients with hypertension or hypercholesterolemia, PPARγ activation with pioglitazone does not affect endothelin-1 activity, despite enhancing insulin sensitivity and reducing plasma insulin and C-reactive protein levels.. In non-diabetic patients with hypertension or hypercholesterolemia, pioglitazone improves insulin sensitivity, lipid profile, and inflammation but does not affect endothelin activity. Our data suggest that the determinants of endothelin-1 vascular activity in vivo may differ and/or be more complex than those suggested by the results of previous in vitro studies.

Topics: Biomarkers; C-Reactive Protein; Cross-Over Studies; District of Columbia; Double-Blind Method; Endothelin A Receptor Antagonists; Endothelin-1; Endothelium, Vascular; Fatty Acids, Nonesterified; Forearm; Humans; Hypercholesterolemia; Hypertension; Insulin; Insulin Resistance; Lipoproteins, HDL; Peptides, Cyclic; Pioglitazone; PPAR gamma; Thiazolidinediones; Time Factors; Treatment Outcome; Triglycerides; Vasodilation

The importance of endothelin-1 in the pathophysiology of essential hypertension is unclear. We therefore examined whether there is a differential effect of endothelin-A antagonism on vasodilation and coronary artery compliance in hypertensive compared to normotensive patients. We examined atherosclerotic non-stenotic arteries from 18 non-diabetic, 10 normotensive patients and eight hypertensive patients, before and after intracoronary infusion of BQ-123 (6 mumol), an endothelin-A receptor antagonist. The systolic and diastolic artery lumen area in the proximal segment was measured using an intravascular ultrasound catheter. Systolic blood pressure decreased only in hypertensive patients (F = 5.44, P = 0.03), after BQ-123 administration. The diastolic artery lumen increased from 8.9 +/- 2.9 mm at baseline to 10.8 +/- 3.0 mm after BQ-123 administration (P < 0.05) in normotensive patients and from 10.6 +/- 4.6 mm to 10.8 +/- 4.0 mm (P = NS) in the hypertensive patients (F = 3.98, P = 0.01). The respective values for the systolic artery lumen, in the two groups, before and after BQ-123 were: 10.2 +/- 3.4 mm and 12.7 +/- 3.2 mm (P < 0.01) in the normotensive group and 12.0 +/- 5.5 mm and 12.8 +/- 5.0 mm (P = NS) in the hypertensive group (F = 3.37, P = 0.08). Artery compliance did not have a differential response to BQ-123. In conclusion, endothelin-A antagonism causes decreased vasodilation but does not have a differential effect on coronary artery compliance in hypertensive patients.

Topics: Adult; Aged; Antihypertensive Agents; Blood Pressure; Compliance; Coronary Vessels; Endothelin A Receptor Antagonists; Endothelin-1; Female; Humans; Hypertension; Infusions, Parenteral; Male; Middle Aged; Peptides, Cyclic; Prospective Studies; Receptor, Endothelin A; Treatment Outcome; Ultrasonography, Interventional; Vasodilation

Essential hypertension is a common disorder, associated with increased endothelin-1-mediated vasoconstrictor tone at rest. We hypothesized that increased vasoconstrictor activity of endothelin-1 might explain why the normal decrease in peripheral vascular resistance in response to exercise is attenuated in hypertensive patients. Therefore, we investigated the effect of endothelin A (ET(A)) receptor blockade on the vasodilator response to handgrip exercise. Forearm blood flow responses to handgrip exercise (15%, 30%, and 45% of maximum voluntary contraction) were assessed in hypertensive patients and matched normotensive subjects, before and after intra-arterial infusions of the ET(A) receptor antagonist BQ-123; a control dilator, hydralazine; and placebo (saline). Preinfusion (baseline) vasodilation in response to exercise was significantly attenuated at each workload in hypertensive patients compared with normotensive subjects. Intra-arterial infusions of hydralazine and saline did not increase the vasodilator response to exercise in either hypertensives or normotensives at any workload. The vasodilator response to exercise was markedly enhanced after BQ-123 at the 2 higher workloads in hypertensives (157+/-48%, P<0.01; 203+/-58%, P<0.01) but not in normotensives. This suggests that the impaired vasodilator response to exercise in hypertensive patients is, at least in part, a functional limitation caused by endogenous ET(A) receptor-mediated vasoconstriction. Treatment with endothelin receptor antagonists may, therefore, increase exercise capacity in essential hypertension.

Topics: Adult; Antihypertensive Agents; Cross-Over Studies; Endothelin Receptor Antagonists; Endothelin-1; Forearm; Hand Strength; Humans; Hydralazine; Hypertension; Infusions, Intra-Arterial; Male; Middle Aged; Peptides, Cyclic; Regional Blood Flow; Single-Blind Method; Time Factors; Vasodilation

Hypertensive patients have both impaired endothelium-dependent vasodilation and increased activity of the endothelin (ET-1) system, which participate in their increased vascular tone and may predispose them to atherosclerosis. This study investigated the contribution of increased ET-1 activity to the impaired endothelium-dependent vasodilator function of hypertensive patients.. Forearm blood flow (FBF) responses to intraarterial infusion of acetylcholine (ACh; 7.5, 15, and 30 microg/min) and sodium nitroprusside (SNP; 0.8,1.6, and 3.2 microg/min) were assessed by strain-gauge plethysmography before and after nonselective blockade of ET(A) and ET(B) receptors by combined infusion of BQ-123 (ET(A) blocker; 100 nmol/min) and BQ-788 (ET(B) blocker; 50 nmol/min). During saline administration, the vasodilator response to ACh was significantly blunted in hypertensive patients compared with controls (P<0.001), whereas the vasodilator effect of SNP was not different between groups (P=0.74). Blockade of ET-1 receptors resulted in a significant increase in FBF from baseline in hypertensive patients (P<0.008) but not in controls (P=0.15). In hypertensive patients, a combined ET(A/B) blockade resulted in a significant potentiation of the vasodilator response to ACh compared with saline (P=0.01), whereas the response to SNP was unchanged (P=0.44). In contrast, the response to ACh was not significantly modified by ET-1 receptor antagonism in healthy subjects (P=0.14 compared with saline).. These findings indicate that blockade of ET-1 receptors improves endothelium-dependent vasodilator function in hypertensive patients, thereby suggesting that an increased ET-1 activity may play a role in the pathophysiology of this abnormality.

Topics: Acetylcholine; Endothelin Receptor Antagonists; Endothelium, Vascular; Female; Forearm; Humans; Hypertension; Infusions, Intra-Arterial; Male; Middle Aged; Nitroprusside; Oligopeptides; Peptides, Cyclic; Piperidines; Receptor, Endothelin A; Regional Blood Flow; Vasodilation; Vasodilator Agents

Neutral endopeptidase (NEP) degrades vasoactive peptides, including the natriuretic peptides, angiotensin II, and endothelin-1. Systemic inhibition of NEP does not consistently lower blood pressure, even though it increases natriuretic peptide concentrations and causes natriuresis and diuresis. We therefore investigated the direct effects of local inhibition of NEP on forearm resistance vessel tone.. Four separate studies were performed, each with 90-minute drug infusions. In the first study, 10 healthy subjects received a brachial artery infusion of the NEP inhibitor candoxatrilat (125 nmol/min), which caused a slowly progressive forearm vasoconstriction (12+/-2%; P=0.001). In a second two-phase study, 6 healthy subjects received, 4 hours after enalapril (20 mg) or placebo, an intra-arterial infusion of the NEP inhibitor thiorphan (30 nmol/min). Thiorphan caused similar degrees of local forearm vasoconstriction (P=0.6) after pretreatment with both placebo (13+/-1%, P=0.006) and enalapril (17+/-6%, P=0.05). In a third three-phase study, 8 healthy subjects received intra-arterial thiorphan (30 nmol/min), the endothelin ETA antagonist BQ-123 (100 nmol/min), and both combined. Thiorphan caused local forearm vasoconstriction (13+/-1%, P=0.0001); BQ-123 caused local vasodilatation (33+/-3%, P=0.0001). Combined thiorphan and BQ-123 caused vasodilatation (32+/-1%, P=0.0001) similar to BQ-123 alone (P=0.98). In a fourth study, 6 hypertensive patients (blood pressure >160/100 mm Hg) received intra-arterial thiorphan (30 nmol/min). Thiorphan caused a slowly progressive forearm vasoconstriction (10+/-2%, P=0.0001).. Inhibition of local NEP causes vasoconstriction in forearm resistance vessels of both healthy volunteers and patients with hypertension. The lack of effect of ACE inhibition on the vasoconstriction produced by thiorphan and its absence during concomitant ETA receptor blockade suggest that it is mediated by endothelin-1 and not angiotensin II. These findings may help to explain the failure of systemic NEP inhibition to lower blood pressure.

Topics: Adult; Aldosterone; Angiotensin II; Angiotensin-Converting Enzyme Inhibitors; Atrial Natriuretic Factor; Blood Pressure; Coronary Vessels; Cross-Over Studies; Cyclohexanecarboxylic Acids; Enalapril; Endothelin-1; Humans; Hypertension; Injections, Intra-Arterial; Male; Middle Aged; Myocardium; Neprilysin; Peptides, Cyclic; Protease Inhibitors; Renin; Single-Blind Method; Thiorphan; Vasoconstriction

Hypertension in obesity is associated with increased insulin resistance, vascular mass and body mass index (BMI). The purpose of the study was to visualize endothelin-1 (ET-1) mediated constriction in arteries isolated from subcutaneous adipose tissue from obese hypertensive women previously operated by gastric bypass. Functional studies were conducted in a microvascular myograph. Expressed as percentage of contraction elicited by 124 mM KCl concentration-response curves for ET-1 were shifted leftward in arteries from obese hypertensive patients compared to healthy normotensive subjects. The vasodilator response to the ET-1 antagonist BQ123 (1 microM) was significantly higher in arteries from obese hypertensive patients (p<0.001). BQ123 induced relaxation was inhibited by NO synthase inhibitor L-NAME (0.1 nM). Preincubation with BQ123 enhanced the relaxation induced by acetylcholine (ACh; 0.1 nM - 0.1 mM) (p<0.001), but not that induced by NO donor sodium nitroprusside (SNP; 0.1 nM - 0.1 mM), in arteries from obese hypertensive patients. The present study show that hypertension yet prevail after gastric bypass surgery and the ET(A) receptor antagonist BQ123 may be a useful tool in reducing blood pressure in obese hypertensive patients.

Topics: Adipose Tissue; Dose-Response Relationship, Drug; Endothelin A Receptor Antagonists; Endothelium, Vascular; Female; Gastric Bypass; Humans; Hypertension; Middle Aged; Obesity; Organ Culture Techniques; Peptides, Cyclic; Receptor, Endothelin A; Vasodilation

Antenatal steroid administration is associated with multiple cardiometabolic alterations, including hypertension; however, the mechanisms underlying this phenomenon are unclear. The aim of the present study was to ascertain, in vivo, the contribution of the endothelin system to the development of hypertension in the adult offspring and the signaling pathway involved. Pregnant sheep were treated with two doses of betamethasone (n = 23) or vehicle (n = 22) at 80 days (~0.55) gestation and allowed to deliver at term. Adult sheep were chronically instrumented under general anesthesia to place vascular catheters and a femoral artery flow probe. Blood pressure and flow were recorded continuously, and femoral artery vascular resistance was calculated before and during administration of endothelin 1 (ET-1). Selective blockers (dantrolene, BQ123, niacinamide) or saline were administered simultaneously. Betamethasone-exposed animals exhibited a significant elevation in mean blood pressure (female: 98 ± 1.8 vs. 92 ± 2.1; males: 97 ± 3.4 vs. 90 ± 2.3; mmHg; P < 0.05). ET-1 elicited a significant increase in blood pressure (F = 56.4; P < 0.001) and in vascular resistance (F = 44.3; P < 0.001) in all groups. A betamethasone effect in the vascular resistance response to ET-1 (F = 25.7; P < 0.001) was present in females only, and the effect was partially blunted by niacinamide (F = 6.6; P < 0.01). Combined administration of niacinamide and BQ123, as well as of dantrolene abolished the betamethasone effect on vascular resistance. No significant differences in mRNA expression of ET(A) or ET(B) in endothelial or smooth muscle cells of resistance-size arteries were observed. We conclude that the betamethasone effect on vascular resistance is mediated by an enhanced response to ET-1 through ET(A) receptor via the cyclic ADPR/ryanodine pathway.

Topics: Animals; Anti-Inflammatory Agents; Betamethasone; Blood Pressure; Dantrolene; Dose-Response Relationship, Drug; Endothelin A Receptor Antagonists; Endothelins; Female; Hypertension; Infusions, Intra-Arterial; Muscle Relaxants, Central; Niacinamide; Nitric Oxide Synthase Type III; Peptides, Cyclic; Pregnancy; Prenatal Exposure Delayed Effects; Regional Blood Flow; RNA, Messenger; Sex Characteristics; Sheep; Vascular Resistance

The contribution of endothelin-1 (ET-1) in a B2KO mouse model of a high salt-induced arterial hypertension was investigated.. Wild-type (WT) or B2KO mice receiving a normal diet (ND) or a high-salt diet (HSD) were monitored by radiotelemetry up to a maximum of 18 weeks. At the 12th week of diet, subgroups under ND or HSD received by gavage the ETA antagonist A127722 during 5 days. In addition, blood samples were collected and, following euthanasia, the lungs, heart and kidneys were extracted, homogenized and assayed for ET-1 by RIA. In a separate series of experiments, the ETA antagonist, BQ123 was tested against the pressor responses to a NOS inhibitor L-N(G)-nitroarginine methyl ester (L-NAME) in anaesthetized WT and B2KO mice.. In B2KO, but not WT mice, 12 weeks of HSD triggered a maximal increase of the mean arterial pressure (MAP) of 19.1 ± 2.8 mmHg, which was corrected by A127722 to MAP levels found in B2KO mice under ND. Significant increases in immunoreactive ET-1 were detected only in the lungs of B2KO mice under HSD. On the other hand, metabolic studies showed that sodium urinary excretion was markedly reduced in B2KO compared with WT mice under ND. Finally, BQ123 (2 mg·kg(-1)) reduced by 50% the pressor response to L-NAME (2 mg·kg(-1)) in B2KO, but not WT mice under anaesthesia.. Our results support the concept that functional B2 receptors oppose high salt-induced increments in MAP, which are corrected by an ETA receptor antagonist in this mouse model of experimental hypertension.

Topics: Animals; Antihypertensive Agents; Arterial Pressure; Atrasentan; Disease Models, Animal; Endothelin A Receptor Antagonists; Endothelin-1; Female; Hypertension; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; NG-Nitroarginine Methyl Ester; Peptides, Cyclic; Pyrrolidines; Receptor, Bradykinin B2; Sodium; Sodium Chloride, Dietary; Telemetry

The aim was to investigate effects of selective endothelin (ET) receptor antagonists on renal hemodynamics and dynamic renal blood flow autoregulation (RBFA) in angiotensin II (Ang II)-infused rats on a high NaCl intake.. Sprague-Dawley rats received Ang II (250 ng/kg/min, s.c.) and an 8% NaCl diet for 14 days after which renal clearance experiments were performed. After baseline measurements animals were administered either: (a) saline vehicle; (b) ETA receptor antagonist BQ-123 (30 nmol/kg/min); (c) ETB receptor antagonist BQ-788 (30 nmol/kg/min); or (d) BQ-123 + BQ-788, for six consecutive 20-minute clearance periods.. BQ-123 reduced arterial pressure (AP) and selectively increased outer medullary perfusion versus vehicle (p<0.05). These effects were attenuated or abolished by combined BQ-123 and BQ-788. BQ-788 reduced renal blood flow and increased renovascular resistance (p<0.05). Ang II-infused rats on high NaCl intake showed abnormalities in dynamic RBFA characterized by an impaired myogenic response that were not significantly affected by ET receptor antagonists.. In hypertensive Ang II-infused rats on a high-NaCl intake selective ETA antagonism with BQ-123 reduced AP and specifically increased OM perfusion and these effects were dependent on intact ETB receptor stimulation. Furthermore, ET receptor antagonists did not attenuate abnormalities in dynamic RBFA.

Topics: Angiotensin II; Animals; Blood Pressure; Disease Models, Animal; Endothelin Receptor Antagonists; Hemodynamics; Hypertension; Kidney; Male; Oligopeptides; Peptides, Cyclic; Piperidines; Rats; Rats, Sprague-Dawley; Regional Blood Flow; Sodium Chloride, Dietary

Experimental evidence indicates that endothelin 1 stimulates the sympathetic nervous system by activation of the subtype A receptor. The aim of the present study was to assess whether this mechanism is active in humans and to investigate its potential role in the pathogenesis of essential hypertension. In 15 hypertensive patients and 12 normotensive subjects, blood pressure, heart rate, and muscle sympathetic nerve activity were evaluated during intravenous 20-minute infusion of BQ123 (0.1 mg/kg per hour), an endothelin A receptor antagonist, and sodium nitroprusside (SNP; 0.4 μg/kg per minute). In hypertensive patients, blood pressure was reduced similarly by BQ123 and SNP. In contrast, the increase in muscle sympathetic nerve activity induced by BQ123 (from 52.0 ± 4.9 to 56.8 ± 5.5 bursts per 100 heartbeats; P<0.05 versus baseline) was significantly lower (P<0.05) than that induced by SNP (from 50.6 ± 4.9 to 61.1 ± 5.1 bursts per 100 heartbeats; P<0.05 versus baseline). In normotensive subjects, SNP reduced blood pressure and increased muscle sympathetic activity, whereas BQ123 was ineffective. Thus, in a subgroup (n = 9) of normotensive subjects, we administered BQ123 at a higher dose (0.2 mg/kg per hour), representing an equidepressor dose of SNP, inducing a blunted increase in sympathetic activity (from 44.1 ± 2.4 to 50.1 ± 6.4 bursts per 100 heartbeats; P<0.05 versus baseline). Finally, administration of a different vasodilator (papaverine, 0.5 mg/kg per hour) exerted results superimposable to SNP. Endogenous endothelin 1 appears to have a sympathoexcitatory effect both in normotensive and hypertensive subjects through endothelin A receptors, contributing to basal sympathetic vasomotor tone. Moreover, essential hypertension shows an increased susceptibility to the sympathoexcitatory effect of endogenous endothelin 1.

Topics: Adult; Antihypertensive Agents; Blood Pressure; Endothelin A Receptor Antagonists; Endothelin-1; Female; Heart Rate; Humans; Hypertension; Male; Middle Aged; Muscles; Nitroprusside; Papaverine; Peptides, Cyclic; Receptor, Endothelin A; Sympathetic Nervous System

Expression of the vasoconstrictor and proinflammatory peptide endothelin (ET)-1 is increased in insulin-resistant (IR) subjects.. The aim of this study was to investigate whether ET-1 regulates skeletal muscle glucose uptake in IR subjects in vivo and in cultured human skeletal muscle cells.. Eleven subjects participated in three protocols using brachial artery infusion of: A) BQ123 (10 nmol/min) and BQ788 (10 nmol/min) (ET(A) and ET(B) receptor antagonist, respectively), followed by coinfusion with insulin (0.05 mU/kg/min); B) insulin alone; and C) insulin followed by coinfusion with ET-1 (20 pmol/min).. Forearm blood flow (FBF) and forearm glucose uptake (FGU) were determined. Glucose uptake and molecular signaling were determined in cultured skeletal muscle cells.. ET(A)/ET(B) receptor blockade increased FGU by 63% (P < 0.05). Coadministration of insulin caused a further 2-fold increase in FGU (P < 0.001). ET(A)/ET(B) receptor blockade combined with insulin resulted in greater FGU than insulin infusion alone (P < 0.005). ET(A)/ET(B) receptor blockade increased FBF by 30% (P < 0.05), with a further 16% increase (P < 0.01) during insulin coinfusion. ET-1 decreased basal FBF by 35% without affecting FGU. ET-1 impaired basal and insulin-stimulated glucose uptake in cultured muscle cells (P < 0.01) via an effect that was prevented by ET(A)/ET(B) receptor blockade.. ET(A)/ET(B) receptor blockade enhances basal and insulin-stimulated glucose uptake in IR subjects. ET-1 directly impairs glucose uptake in skeletal muscle cells via a receptor-dependent mechanism. These data suggest that ET-1 regulates glucose metabolism via receptor-dependent mechanisms in IR subjects.

Topics: Biological Transport; Blood Glucose; Body Mass Index; Brachial Artery; C-Reactive Protein; Endothelin-1; Forearm; Glucose; Glycated Hemoglobin; Humans; Hypertension; Infusions, Intra-Arterial; Insulin; Insulin Resistance; Male; Middle Aged; Muscle, Skeletal; Oligopeptides; Peptides, Cyclic; Piperidines; Regional Blood Flow; Triglycerides

We have reported that eucapnic intermittent hypoxia (E-IH) causes systemic hypertension, elevates plasma endothelin 1 (ET-1) levels, and augments vascular reactivity to ET-1 and that a nonspecific ET-1 receptor antagonist acutely lowers blood pressure in E-IH-exposed rats. However, the effect of chronic ET-1 receptor inhibition has not been evaluated, and the ET receptor subtype mediating the vascular effects has not been established. We hypothesized that E-IH causes systemic hypertension through the increased ET-1 activation of vascular ET type A (ET(A)) receptors. We found that mean arterial pressure (MAP) increased after 14 days of 7 h/day E-IH exposure (109 +/- 2 to 137 +/- 4 mmHg; P < 0.005) but did not change in sham-exposed rats. The ET(A) receptor antagonist BQ-123 (10 to 1,000 nmol/kg iv) acutely decreased MAP dose dependently in conscious E-IH but not sham rats, and continuous infusion of BQ-123 (100 nmol.kg(-1).day(-1) sc for 14 days) prevented E-IH-induced increases in MAP. ET-1-induced constriction was augmented in small mesenteric arteries from rats exposed 14 days to E-IH compared with those from sham rats. Constriction was blocked by the ET(A) receptor antagonist BQ-123 (10 microM) but not by the ET type B (ET(B)) receptor antagonist BQ-788 (100 microM). ET(A) receptor mRNA content was greater in renal medulla and coronary arteries from E-IH rats. ET(B) receptor mRNA was not different in any tissues examined, whereas ET-1 mRNA was increased in the heart and in the renal medulla. Thus augmented ET-1-dependent vasoconstriction via vascular ET(A) receptors appears to elevate blood pressure in E-IH-exposed rats.

Topics: Animals; Antihypertensive Agents; Blood Pressure; Coronary Vessels; Disease Models, Animal; Dose-Response Relationship, Drug; Endothelin A Receptor Antagonists; Endothelin B Receptor Antagonists; Endothelin-1; Hypertension; Hypoxia; Infusions, Parenteral; Male; Mesenteric Arteries; Oligopeptides; Peptides, Cyclic; Piperidines; Rats; Rats, Sprague-Dawley; Receptor, Endothelin A; Renal Artery; Time Factors; Vasoconstriction

We report in the present study the role of endothelin (ET-1) and ET-1 receptors in the sustained hypoxia-induced systemic hypertension.. Wistar rats were randomly assigned to live continuously in hypobaric hypoxia (CH rats) or normoxia (N rats). At the end of hypoxic stress exposure (5 weeks at 450 mm Hg), measurements of mean systemic arterial pressure were done. The effects of ET-1 in the presence or not of the endothelium and/or of specific ET-A inhibitors (BQ-123) or ET-B inhibitors (BQ-788), have been investigated in an isolated model of rat thoracic aorta. Finally, plasmatic ET-1 concentrations have been determined by assay procedure.. Following five weeks of chronic hypoxic stress, CH rats presented a significant increase of mean systemic arterial pressure (N: 129.1+/-6.8 mm Hg vs CH: 152.5+/-3.4 mm Hg; P<0.05). Despite of this hypoxia-induced hypertension, ET-1 plasmatic concentration was not different between N and CH rats. Finally, CH rats presented a reduce response to ET-1 when compared to N rats. This phenomenon seems to be associated to the ET-A vascular smooth muscle cell receptors, since difference between N and CH rats was still present in endothelium denuded aortic rings in the presence or not of the specific ET-B inhibitors (BQ-788). In addition, in the presence of the specific ET-A inhibitor (BQ-123) response to ET-1 was abolished in N and CH rats to the same extent (N:-98%; CH:-99%).. This work clearly suggests that, following long term exposure to hypoxia, ET-1 and ET-1 receptors are not involved in the persistence of systemic hypertension in a rat model, and that chronic exposure to severe hypoxic stress was associated with a downregulation of the ET-A receptors response to ET-1.

Topics: Animals; Aorta, Thoracic; Endothelin-1; Hypertension; Hypoxia; In Vitro Techniques; Male; Muscle, Smooth, Vascular; Oligopeptides; Peptides, Cyclic; Piperidines; Rats; Rats, Wistar; Receptor, Endothelin A; Receptor, Endothelin B; Vasoconstriction

In the present paper, the age-related changes in the vasoconstrictive endothelin-mediated response to insulin in aortas of normal and hypertensive, hypertriglyceridemic, hyperinsulinemic (HTG) rats were studied. To develop HTG rats, weanling male Wistar animals were given 30% sucrose in their drinking water for 4, 6, 12 and 18 months. Blood pressure was increased in HTG rats for up to 12 months showing a maximum at 6 months (138.9+/-0.8 mmHg). In vitro contractions were elicited with 40 mM KCl in the presence and absence 50 microU/ml insulin and of endothelin-receptor antagonists BQ123 and BQ788. Tension development to KCl was not modified during aging in control rats but was increased at 4 and 6 months in HTG rats. Increased endothelin release induced by insulin remained constant in normal rats, while in HTG rats it was higher than in controls at all ages. ET(A) blocker participation alone increased during aging in control rats while both receptor blockers participated in HTG rats. Our results suggest that the vasoconstrictive capacity to KCl plus insulin decreases during aging and that this decrease is greater in HTG rats. The participation of endothelin receptors in the aging process differs in control and HTG rats.

Topics: Aging; Animals; Antihypertensive Agents; Aorta; Blood Glucose; Blood Pressure; Endothelin Receptor Antagonists; Endothelins; Hypertension; Hypertriglyceridemia; Hypoglycemic Agents; Insulin; Insulin Resistance; Male; Oligopeptides; Peptides, Cyclic; Piperidines; Potassium Chloride; Rats; Rats, Wistar; Triglycerides; Vasoconstriction; Weight Loss

Activation of renal mechanosensory nerves is enhanced by high and suppressed by low sodium dietary intake. Afferent renal denervation results in salt-sensitive hypertension, suggesting that activation of the afferent renal nerves contributes to water and sodium balance. Another model of salt-sensitive hypertension is the endothelin B receptor (ETBR)-deficient rat. ET and its receptors are present in sensory nerves. Therefore, we examined whether ET receptor blockade altered the responsiveness of the renal sensory nerves. In anesthetized rats fed high-sodium diet, renal pelvic administration of the ETBR antagonist BQ-788 reduced the afferent renal nerve activity (ARNA) response to increasing renal pelvic pressure 7.5 mmHg from 26+/-3 to 9+/-3% and the PGE2-mediated renal pelvic release of substance P from 9+/-1 to 3+/-1 pg/min. Conversely, in rats fed low-sodium diet, renal pelvic administration of the ETAR antagonist BQ-123 enhanced the ARNA response to increased renal pelvic pressure from 9+/-2 to 23+/-6% and the PGE2-mediated renal pelvic release of substance P from 0+/-0 to 6+/-1 pg/min. Adding the ETAR antagonist to ETBR-blocked renal pelvises restored the responsiveness of renal sensory nerves in rats fed a high-sodium diet. Adding the ETBR antagonist to ETAR-blocked pelvises suppressed the responsiveness of the renal sensory nerves in rats fed a low-sodium diet. In conclusion, activation of ETBR and ETAR contributes to the enhanced and suppressed responsiveness of renal sensory nerves in conditions of high- and low-sodium dietary intake, respectively. Impaired renorenal reflexes may contribute to the salt-sensitive hypertension in the ETBR-deficient rat.

Topics: Animals; Antihypertensive Agents; Diet, Sodium-Restricted; Endothelin A Receptor Antagonists; Endothelin B Receptor Antagonists; Endothelins; Ganglia, Spinal; Gene Expression Regulation; Hypertension; Kidney; Male; Mechanotransduction, Cellular; Neurons, Afferent; Oligopeptides; Peptides, Cyclic; Piperidines; Rats; Rats, Sprague-Dawley; Receptor, Endothelin A; Receptor, Endothelin B; Sodium, Dietary; Substance P

Angiotensin II and endothelin-1 (ET) are two hormones involved in cardiovascular diseases and well known for their capacity to induce free radical generation in vascular and cardiac tissues. In addition to its prooxidative effect, angiotensin II can increase the synthesis of ET-1 in vascular smooth muscle cells (VSMC). Our objective was to determine whether the ET-1 synthesis in VSMC is involved in angiotensin II-induced superoxide anion production in rats. Our results show that treatments of isolated VSMC with angiotensin II and ET increased superoxide. However, this increase occurred in a bimodal fashion for angiotensin II with a fast transient production (10 min) and a late sustained production (6 h), while ET-1 induced superoxide formation after a delay of 6 h. LU302872 and BQ-123, a nonselective and a selective ETA receptor antagonists, respectively, prevented angiotensin II-induced superoxide anion production only during the late phase. In contrast, BQ-3020, a selective ETB receptor antagonist, had no effect. In vivo, LU302872 reduced the aortic superoxide production induced by angiotensin II administered for 12 days. In conclusion, our results suggest that the superoxide generation induced by chronic angiotensin II infusion may be mediated by ET-1 acting on ETA receptors in VSMC in vitro. Furthermore, this effect appears to contribute to the excess superoxide production during the chronic activation of the renin-angiotensin system in vivo.

Topics: Angiotensin II; Animals; Antihypertensive Agents; Cells, Cultured; Endothelin Receptor Antagonists; Endothelin-1; Hypertension; In Vitro Techniques; Male; Muscle, Smooth, Vascular; NADH, NADPH Oxidoreductases; NADPH Oxidase 1; NADPH Oxidase 4; NADPH Oxidases; Peptides, Cyclic; Propionates; Pyrimidines; Rats; Rats, Sprague-Dawley; Superoxides

Hypertensive patients have increased endothelin-1-dependent vasoconstrictor tone. This abnormality, however, might not be uniformly present in all forms of hypertension, as suggested by experimental studies showing that endothelin-1 activity is enhanced predominantly in low-renin, high-volume models and in insulin-resistant states. Because hypertension in obesity is commonly associated with both expanded plasma volume and insulin resistance, this study sought to determine whether increased body mass index (BMI) in hypertensive patients relates to activation of the endothelin-1 system. Forearm blood flow (FBF) responses (plethysmography) to intra-arterial infusion of an ETA receptor blocker (BQ-123) were analyzed in hypertensive patients and normotensive control subjects according to BMI. The vasodilator response to BQ-123 was significantly higher in hypertensive patients than in control subjects (P<0.001). During BQ-123, a significant increase in FBF from baseline was observed in obese (BMI > or =30 kg/m2; P<0.001) and overweight (BMI, 27 to 29.9 kg/m2; P=0.04) but not in lean (BMI <27 kg/m2; P=0.83) hypertensive patients. In contrast, no significant change in FBF was observed during BQ-123 either in obese (P=0.53), overweight (P=0.76), or lean (P=0.93) normotensive subjects. Moreover, a significant correlation between BMI and the vasodilator response to ETA blockade was observed in hypertensive subjects (R=0.53; P=0.005) but not in control subjects (R=0.11; P=0.58). In human hypertension, increased BMI is associated with enhanced ETA-dependent vasoconstrictor activity, suggesting that this abnormality may play a role in the pathophysiology of obesity-related hypertension and that targeting the endothelin-1 system may be useful in the treatment of these patients.

Topics: Body Mass Index; Endothelin A Receptor Antagonists; Endothelin-1; Female; Forearm; Humans; Hypertension; Male; Middle Aged; Obesity; Peptides, Cyclic; Regional Blood Flow; Vasodilation

1. The roles of nitric oxide (NO), superoxide anion (O(2)(-)), and hydrogen peroxide (H(2)O(2)) in the modulation of spontaneous tone were investigated in isolated aorta from deoxycorticosterone acetate (DOCA)-salt hypertensive rats. 2. Increases in preload from 1 to 5 g were accompanied by increases in spontaneous tone in aortic rings from DOCA-salt hypertensive rats but not from SHAM-normotensive rats. 3. Tone was higher in endothelium-denuded aortic rings than in endothelium-intact vessels. Inhibition of nitric oxide synthase (NOS) with 300 microM N(G)-nitro-L-arginine methyl ester (l-NAME) increased spontaneous tone. 4. Basal O(2)(-) generation was higher in aortic rings from DOCA-salt hypertensive rats than in those from SHAM-normotensive rats. Stretch increased O(2)(-) levels even further in the DOCA-salt group. In rings isolated from DOCA-salt hypertensive rats, administration of the O(2)(-) scavenger, superoxide dismutase (SOD, 150 U ml(-1)), or the nicotinamide adenine dinucleotide phosphate (NADPH)-oxidase inhibitor, apocynin (100 microM), completely abolished the development of spontaneous tone in endothelium-intact aortic rings but not in endothelium-denuded or in L-NAME-treated rings. SOD and apocynin decreased the generation of O(2)(-) in endothelium-intact, endothelium-denuded, and L-NAME-treated aortic rings. 5. Oral treatment of DOCA-salt hypertensive rats with the O(2)(-) scavengers, tempol or tiron, or with apocynin for 3 weeks prevented the development of hypertension and abolished the increases in O(2)(-) generation and spontaneous tone. 6. Administration of catalase (1000 U ml(-1)) to aortic rings increased spontaneous tone in vessels from DOCA-salt hypertensive rats. 7. Administration of the cyclooxygenase (COX) inhibitor, valeroyl salicylate, or the thromboxane/prostaglandin antagonist, SQ 29548, to aortic rings abolished tone. 8. The results suggest that NO plays a major role in preventing the generation of spontaneous tone in isolated aortic rings from DOCA-salt hypertensive rats. NADPH-oxidase-derived O(2)(-) enhanced spontaneous tone by inactivating NO. Endogenous H(2)O(2) appears to mitigate the increase in tone. In addition, a COX component may also contribute to spontaneous tone.

Topics: Acridines; Animals; Aorta, Thoracic; Blood Pressure; Blotting, Western; Calcium; Catalase; Cyclooxygenase Inhibitors; Desoxycorticosterone; Endothelium, Vascular; Hydrogen Peroxide; Hypertension; Immunohistochemistry; In Vitro Techniques; Luminescent Measurements; Male; Muscle Contraction; Muscle Tonus; Muscle, Smooth, Vascular; Nitric Oxide; Nitric Oxide Synthase; Nitric Oxide Synthase Type III; Oligopeptides; Oxidative Stress; Oxygen; Peptides, Cyclic; Piperidines; Rats; Rats, Sprague-Dawley; Receptors, Thromboxane; Superoxides; Tyrosine; Xanthine Oxidase

The pathogenesis of essential hypertension in blacks may differ from that in whites. In particular, black patients usually present with a salt-sensitive, low-renin form, which in animal models is associated with enhanced activity of endothelin-1 (ET-1). This study aimed to assess whether ethnic differences exist in the vascular activity of ET-1 in normotensive and hypertensive blacks and whites.. Forearm blood flow (FBF) responses to intraarterial infusion of an ET(A) receptor blocker (BQ-123) were analyzed by plethysmography in 37 normotensive patients and 27 hypertensive patients according to race. BQ-123 did not affect FBF in normotensive subjects (P=0.30), whereas it produced significant vasodilation in hypertensive subjects (P<0.001). In normotensives, FBF response to BQ-123 was similar in white (n =22) and black (n =15) patients (P=0.85). In contrast, in hypertensive patients, the vasodilator effect of ET(A) receptor blockade was significantly higher in blacks (n =13) than in whites (n =14) (P=0.01). To rule out differences in smooth muscle reactivity, the effects of race on FBF responses to exogenous ET-1 were analyzed in the hypertensive subgroups. Endothelin-1 induced a significant vasoconstriction in both white (n =7) and black patients (n =5) (both P<0.001), without differences between them (P=0.46). In 8 black hypertensives, the response to selective ET(A) blockade was not modified by nonselective blockade of ET-1 receptors by co-infusion of BQ-123 and BQ-788 (P=0.66).. Hypertensive blacks have enhanced ET(A)-dependent vasoconstrictor tone, probably related to increased production of ET-1. Given the negative vascular effects of ET-1, this abnormality may contribute to the pathogenesis of hypertension and its complications in black patients.

Topics: Black People; Endothelin A Receptor Antagonists; Endothelin B Receptor Antagonists; Endothelin-1; Female; Forearm; Humans; Hypertension; Male; Middle Aged; Oligopeptides; Peptides, Cyclic; Piperidines; Plethysmography; Vasoconstriction; White People

Endothelin (ET)-1 contributes to raising blood pressure (BP) and inducing cardiovascular disease by vasoconstriction and potent stimulation of aldosterone secretion. In the rat this latter effect occurs via ET(B) receptors; in humans in vitro studies implicated both ET(A) and ET(B) receptors, but there is no conclusive evidence in vivo.. We recruited 13 consenting hypertensive patients: six with primary aldosteronism (PA) and seven with high-to-normal renin hypertension (HNRH). They were infused with a low dose (200 nmol/min for 5 min followed by 100 nmol/min for 10 min) of the ET(A)-selective antagonist BQ-123 either alone or, on a different day, together with an identical dose of the ET(B)-selective antagonist BQ-788. Plasma aldosterone, cortisol and ACTH concentration and plasma renin activity (PRA) were measured with radioimmunoassay at -15, 0, 30, 60, 120, 240, 360 min, while BP was recorded non-invasively.. BQ-123 alone and combined with BQ-788 significantly lowered mean BP in both PA and HNRH patients (by 6-10 mmHg at nadir; P<0.01). In PA patients, a short-lived decrease of aldosterone was elicited by combined BQ-123 and BQ-788 (-14%; P<0.05), but not by BQ-123 alone; cortisol, ACTH, and PRA were unaffected by either treatment. In HNRH patients, BQ-123 both alone and combined with BQ-788 lowered aldosterone (-39 and -28%, respectively) and PRA (-43 and -16%, respectively), while cortisol and ACTH were unaffected.. Endogenous ET-1 contributes to maintaining the high BP values and the aldosterone secretion in both PA and HNRH patients. In the former patients, the aldosterone secretagogue effect of ET-1 is mediated via ET(B) receptors, while in the latter it occurs mainly via ET(A)-mediated stimulation of renin production.

Topics: Adrenocorticotropic Hormone; Aldosterone; Endothelin Receptor Antagonists; Female; Humans; Hydrocortisone; Hyperaldosteronism; Hypertension; Infusions, Intravenous; Male; Middle Aged; Oligopeptides; Peptides, Cyclic; Piperidines; Renin

Endothelin-1 (ET-1) is a potent vasoconstrictor that increases vascular tone in the resistance vessels of subjects with hypertension. It is unclear whether endogenous ET-1 affects resistance-vessel function equally in patients with other cardiovascular risk factors. Vasoconstriction to ET-1 is mediated principally via the endothelin-A (ETA) receptor on vascular smooth muscle cells. Accordingly, we used an ETA-specific antagonist, BQ-123, to test the hypothesis that endogenous ET-1 increases vascular resistance selectively in subjects with hypertension compared with other risk factors. BQ-123 was infused at 100 nmol/min for 80 minutes into the brachial artery of 10 subjects with hypertension (mean+/-SEM arterial pressure, 106+/-5 mm Hg), 12 subjects with hypercholesterolemia (mean+/-SEM total cholesterol, 7.1+/-0.2 mmol/L), 10 active smokers (mean+/-SEM, 42+/-11 pack-years), and 11 healthy, age-matched individuals. Forearm blood flow (FBF) was measured by venous occlusion plethysmography. BQ-123 dilated resistance arterioles in hypertensive subjects, with FBF's increasing by 46+/-7% from baseline (P<0.001). BQ-123 increased FBF to a lesser extent in hypercholesterolemic (24+/-5%, P<0.001) and healthy (20+/-8%, P=0.007) individuals but did not affect FBF significantly in smokers (10+/-8%, P=0.185). The vasodilator response in hypertensive subjects, but not in hypercholesterolemic patients or smokers, was significantly greater than that in healthy individuals (P=0.012). Endogenous ET-1, acting via the ETA receptor, increases resistance-vessel tone in subjects with hypertension more than in subjects with hypercholesterolemia or in smokers. These results indicate that ET-1 contributes more to the pathophysiology of hypertension than of other risk factors in subjects without overt atherosclerosis.

Topics: Arteriosclerosis; Endothelin Receptor Antagonists; Endothelin-1; Female; Forearm; Humans; Hypercholesterolemia; Hypertension; Male; Middle Aged; Peptides, Cyclic; Receptor, Endothelin A; Regional Blood Flow; Risk Factors; Smoking; Vascular Resistance; Vasodilation

The importance of endothelin-1 (ET-1) in the pathophysiology of essential hypertension is unclear. We therefore compared the effects of endothelin ET(A) receptor blockade and the stimulation of ET(A) and ET(B) receptors, and their interaction with the sympathetic nervous system, in the forearm resistance vessels of patients with essential hypertension and healthy control subjects. A total of 27 untreated patients with essential hypertension (blood pressure >160/100 mmHg) and 25 normotensive (blood pressure <140/90 mmHg) age- and sex-matched control subjects participated in these studies. A total of 10 patients and 10 controls took part in each phase. Locally active doses of study drugs were infused into the non-dominant brachial artery, while forearm blood flow was measured by venous occlusion plethysmography. A 60 min infusion of BQ-123 (an ET(A) receptor antagonist; 100 nmol/min) significantly increased forearm blood flow by 40+/-8% in hypertensive patients and by 35+/-5% in controls, with no difference between groups (P=0.49). Forearm vasoconstriction to ET-1 (an ET(A) and ET(B) receptor agonist; 5 pmol/min) for 90 min was significantly blunted in hypertensive patients (21+/-4%) compared with control subjects (37+/-3%; P=0.0001). Forearm vasoconstriction to sarafotoxin S6c (an ET(B) receptor agonist; 10 pmol/min) for 90 min was similar in hypertensive patients (44+/-5%) and control subjects (48+/-4%; P=0.95). Sympathetically mediated vasoconstriction produced by lower-body negative pressure was not different in hypertensive patients compared with controls, and was not affected by infusion of ET-1 or sarafotoxin S6c. There were no differences in the observed increase in forearm blood flow with a control vasodilator (sodium nitroprusside) or the observed decrease in forearm blood flow with a control vasoconstrictor (noradrenaline) between hypertensive patients and control subjects. BQ-123 produced a significant increase in forearm blood flow in hypertensive patients, consistent with the anti-hypertensive actions of this agent. In conclusion, forearm vasoconstriction to ET-1, but not to sarafotoxin S6c, was reduced in patients with essential hypertension, consistent with possible down-regulation of the ET(A) receptor in this condition.

Topics: Acetylcholine; Brachial Artery; Case-Control Studies; Endothelin Receptor Antagonists; Endothelin-1; Female; Humans; Hypertension; Male; Middle Aged; Nitroprusside; Norepinephrine; Peptides, Cyclic; Receptor, Endothelin A; Receptors, Endothelin; Regional Blood Flow; Vasoconstrictor Agents; Vasodilator Agents; Viper Venoms

Mice with disruption of the kinin B(2) receptor (B(2)KO mice) are sensitive to salt-rich diets, which causes hypertension. The aim of the study was to assess the role of endothelin-1 (ET-1) and angiotensin-II in hypertensive B(2)KO mice on a salt-rich diet. We also wanted to verify if there is an upregulation of the mRNA expression of the precursors or receptors for these hormones. Two groups of B(2)KO mice (20-25 g) were investigated. The first group received an 8% NaCl diet with 1% NaCl in drinking water (HS) and the second was fed with normal food with tap water (NS). The antagonists tested were the ET(A) receptor antagonist BQ-123 (1 and 5 mg/kg), the ET(B) receptor antagonist BQ-788 (0.25 and 1 mg/kg), the angiotensin receptor type 1 antagonist losartan (10 mg/kg) and the angiotensin-converting enzyme inhibitor captopril (3 mg/kg). These were injected intraperitoneally 30 min prior to blood pressure measurement by the tail-cuff method. We also studied the level of expression of preproET-1, ET-1 receptors, angiotensinogen and angiotensin receptors by RNA extraction from the heart and kidneys of these mice followed by reverse transcriptase (RT)-PCR. B(2)KO mice (HS) were hypertensive after 8 weeks compared with B(2)KO mice on normal diet (HS, 93.4+/-1.5 mmHg, n=7; NS, 61.4+/-2.7 mmHg, n=7). In the HS group, the mean arterial blood pressure was significantly reduced by BQ-123 (5 mg/kg) to 61.9+/-1.8 mmHg (n=7), by BQ-788 (1 mg/kg) to 58.8+/-2.6 mmHg (n=6), by losartan (10 mg/kg) to 73.2+/-1.7 mmHg (n=8) and by captopril (3 mg/kg) to 86.0+/-2.3 mmHg (n=8). The expression studied by RT-PCR did not show any difference (either in precursors or receptors expression) between hypertensive and normal mice. The four antagonists used seemed to reverse the hypertension. These results suggest that ET-1 and angiotensin-II are probably involved in the mechanism that leads to hypertension since the effect of these hormones is probably not compensated by kinins in B(2)KO mice. Further studies are necessary to understand the implication of the cross-talk between these hormones in the hypertensive state.

Topics: Angiotensin II; Angiotensin Receptor Antagonists; Angiotensin-Converting Enzyme Inhibitors; Animals; Captopril; Endothelin Receptor Antagonists; Endothelin-1; Endothelins; Female; Hypertension; Kidney; Losartan; Male; Mice; Mice, Knockout; Myocardium; Oligopeptides; Peptides, Cyclic; Piperidines; Protein Precursors; Receptor, Bradykinin B2; Receptor, Endothelin A; Receptor, Endothelin B; Receptors, Angiotensin; Receptors, Bradykinin; Receptors, Endothelin; RNA, Messenger; Sodium Chloride, Dietary

Topics: Endothelin Receptor Antagonists; Forearm; Humans; Hypertension; Indans; Infusions, Intra-Arterial; Peptides, Cyclic; Regional Blood Flow; Vasodilation

In this study we investigated the role of endogenous endothelin in the cardiovascular response to acute stress, ie mild footshocks in conscious rats. Footshock-stress significantly increased mean arterial pressure and heart rate (P < 0.05). Peripheral or intracerebroventricular (IVT) administration of BQ 788, a selective antagonist of ET(B) receptor, did not alter pressor response to footshocks. Intraperitoneal injections of BQ 123 (1 mg/kg), a selective antagonist of the ET(A)-receptor, had a tendency to decrease, while BQ 123 (203 ng/5 microl) IVT administration significantly reduced the pressor response to footshocks (-12 mm Hg, P < 0.001). Neither ET(A) nor ET(B) antagonists, when injected centrally or peripherally, altered basal blood pressure or heart rate. Our results may indicate a role of brain endothelin in the sympathetic mediated cardiovascular response to stress, via stimulation of ET(A) receptor.

Topics: Analysis of Variance; Animals; Antihypertensive Agents; Electroshock; Endothelin Receptor Antagonists; Endothelins; Hypertension; Male; Oligopeptides; Peptides, Cyclic; Piperidines; Rats; Rats, Sprague-Dawley

1. We previously reported that activation function of mitogen-activated protein kinases (MAPK) is enhanced in aorta strips from both prehypertensive and hypertensive spontaneously hypertensive rats (SHR) and that this enhancement of MAPK activation results from enhanced MAPK activation reactivity to angiotensin (Ang) II in SHR aorta strips. 2. The purpose of the present study was to examine whether the enhanced function of the vascular angiotensin system observed in SHR aorta strips results from genetic alterations of vascular smooth muscle cells from SHR. 3. Basal MAPK activity was within normal limits in cells from 4-week-old SHR, whereas enzyme activity was enhanced in 9-week-old SHR compared with age-matched Wistar-Kyoto (WKY) rats. 4. Mitogen-activated protein kinase activation reactivity to AngII and endothelin-1 was enhanced in 9-week-old SHR cells but not in 4-week-old SHR cells. The enhancement of basal MAPK activity in 9-week-old SHR cells was abolished by a combination of the angiotensin AT(1) receptor antagonist losartan and the endothelin receptor antagonist BQ123. 5. These findings suggest that MAPK activation function in 4-week-old SHR cells is not enhanced. Thus, it appears that factors outside vascular smooth muscle cells are needed for the enhanced MAPK activation observed in 4-week-old SHR aorta strips. In 9-week-old SHR, MAPK activation function is enhanced in cells themselves and this function may, at least in part, contribute to the enhanced MAPK activation observed in SHR aorta strips.

Topics: Aging; Animals; Aorta, Thoracic; Cells, Cultured; Dose-Response Relationship, Drug; Enzyme Activation; Enzyme Inhibitors; Genetic Predisposition to Disease; Hypertension; Losartan; Male; Mitogen-Activated Protein Kinases; Muscle, Smooth, Vascular; Peptides, Cyclic; Rats; Rats, Inbred SHR; Rats, Inbred WKY

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

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

Endothelin (ET) and the sympathoadrenal system contribute to the development and maintenance of deoxycorticosterone acetate (DOCA)-salt hypertension. ET can act directly on the adrenal medulla to enhance the release of catecholamines. In addition, the level of ET peptide is increased in the adrenal glands of DOCA-salt hypertensive rats. Therefore, we tested the hypothesis that ET enhances adrenal medullary catecholamine release during DOCA-salt hypertension. The infusion of exogenous ET-1 into an isolated, perfused adrenal gland preparation resulted in an increase in the basal release of norepinephrine (NE) and epinephrine (EPI) in control and DOCA-salt hypertensive rats. Nerve-stimulated (0.3 Hz) release of NE was significantly inhibited during ET-1 infusion in the DOCA-salt hypertensive rats but not in the control rats. The role of endogenous ET on basal and nerve-stimulated NE and EPI release was also examined. An infusion of either BQ-123 (10(-7) mol/L), an ET(A) receptor antagonist, or BQ-788 (10(-7) mol/L), an ET(B) receptor antagonist, did not alter basal NE or EPI release in either control or DOCA-salt hypertensive rats. BQ-788 did not alter nerve-stimulated release of NE and EPI. In contrast, the nerve-stimulated release of EPI, but not NE, was enhanced during BQ-123 infusion in DOCA-salt hypertensive rats. Nerve-stimulated NE and EPI release was unaffected by BQ-123 in the control rats. These data suggest that ET can stimulate adrenal medullary catecholamine release in normotensive and DOCA-salt hypertensive rats. However, ET also inhibits adrenal medullary catecholamine release in DOCA-salt hypertensive rats.

Topics: Adrenal Medulla; Animals; Antihypertensive Agents; Blood Pressure; Desoxycorticosterone; Electric Stimulation; Endothelin Receptor Antagonists; Endothelin-1; Epinephrine; Heart Rate; Hypertension; Infusions, Intravenous; Male; Nephrectomy; Norepinephrine; Oligopeptides; Peptides, Cyclic; Piperidines; Rats; Rats, Sprague-Dawley; Receptor, Endothelin A; Receptor, Endothelin B; Sodium Chloride; Sodium Chloride, Dietary; Splanchnic Nerves

To analyse the effects of endothelin-1 and vasopressin on the sympathetic vasoconstriction during hypertension.. Electrical field stimulation (4 Hz) was applied to isolated, 2 mm segments of the tail artery from spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) rats prepared for isometric tension recording.. The contraction to electrical stimulation was potentiated by endothelin-1 (10(-10)-10(-8) M) in arteries from WKY but not from SHR, and by vasopressin (10(-12)-10(-10) M) more markedly in arteries from WKY than from SHR. The potentiation by endothelin-1 was reduced more markedly by the antagonist of endothelin ETA receptors BQ-123 (10(-5) M) than by the endothelin ETB receptor antagonist BQ-788 (10(-5) M). The potentiation by vasopressin was reduced by the antagonist of vasopressin V1 receptors d(CH2)5Tyr(Me)AVP (10(-7) M), but not by the vasopressin V2 receptor antagonist d(CH2)5D-Ile2, Ile4AVP (10(-7) M). The blocker of L-type calcium channels verapamil (10(-5) M) reduced the potentiation by both endothelin-1 and vasopressin in arteries from WKY rats, and increased the potentiation by vasopressin in arteries from SHR. Noradrenaline (10(-8)-10(-4) M) contraction was not modified by endothelin-1 (3 x 10(-9) M) or vasopressin (3 x 10(-11) M), and contraction to endothelin-1 (10(-9)-10(-7) M) and vasopressin (10(-10)-10(-7) M) was lower in arteries from SHR than from WKY rats.. (1) The potentiation by endothelin-1 and vasopressin of the sympathetic vasoconstriction, probably due to increased release of noradrenaline, is impaired during hypertension, and (2) this potentiation is mediated mainly by endothelin ETA receptors, and by vasopressin V1 receptors, in both WKY and SHR, and for both peptides it is mediated by L-type calcium channels in arteries from normotensive but not in those from hypertensive animals.

Topics: Animals; Antidiuretic Hormone Receptor Antagonists; Arginine Vasopressin; Calcium Channel Blockers; Electric Stimulation; Endothelin Receptor Antagonists; Endothelin-1; Hypertension; In Vitro Techniques; Male; Norepinephrine; Oligopeptides; Peptides, Cyclic; Piperidines; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Vasoconstriction; Vasopressins; Verapamil

To assess whether primary changes in endothelin-1 (ET-1) receptor responsiveness or secondary vessel functional modifications could characterize the effects evoked by ET-1 in the mesenteric vascular bed (MVB) of prehypertensive 5-week-old and 12-week-old spontaneously hypertensive rats (SHRs).. We used male 5-week-old and 12-week-old SHRs and sex- and age-matched Wistar-Kyoto (WKY) rats as controls. ET-1 receptor responsiveness was evaluated by ET-1 (0.04-2 micromol/l) concentration-response curves and repeated with indomethacin and BQ-123 (0.1-0.5 micromol/l), the latter a selective ETA receptor antagonist. ETB receptor responsiveness was tested by sarafotoxin S6c (1-100 nmol/l) and IRL-1620 (0.1-10 nmol/l) concentration-response curves, obtained in the noradrenaline-precontracted MVB.. At 5 weeks of age, ET-1 induced a similar concentration-dependent contraction in SHRs and WKY rats, with an overlapping BQ-123 pA2 value (negative common logarithm of the antagonist that produces an agonist dose ratio of 2) in the two strains. Indomethacin was ineffective in both groups. Sarafotoxin S6c and IRL-1620 both evoked an ETB-mediated, significant relaxation, only in WKY rats. In 12-week-old SHRs, ET-1 evoked a markedly increased maximal effect compared with the response in WKY rats (P< 0.01); this was prevented by treatment with indomethacin. The BQ-123 pA2 value was higher in SHRs than in WKY rats (P< 0.01). Both sarafotoxin S6c and IRL-1620 evoked a significant concentration-dependent relaxation in WKY rats, which was not detected in SHR preparations.. Our results could suggest that the different responses evoked by ET-1 in the MVB of SHRs during the onset of hypertension may be related partially to primary alterations in the ET-1 receptorial pattern and partially to the onset of high blood pressure, leading to an impairment in the haemodynamic balance.

Topics: Aging; Animals; Anti-Inflammatory Agents, Non-Steroidal; Antihypertensive Agents; Endothelin Receptor Antagonists; Endothelin-1; Endothelins; Hypertension; Indomethacin; Mesenteric Arteries; Norepinephrine; Peptide Fragments; Peptides, Cyclic; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Receptor, Endothelin A; Receptors, Endothelin; Vascular Resistance; Vasoconstrictor Agents; Viper Venoms

The objective of the present study was to determine if endothelin-1 played a role in the elevated peripheral resistance in deoxycorticosterone-acetate (DOCA)-salt hypertension. Radioimmunoassay showed that the concentration of endothelin-1 was higher in thoracic aorta of the DOCA-salt group than that of the control normotensive (CN) group. Responses of arterioles in the rat cremaster to endothelin-1 were also observed using in vivo closed circuit television microscopy. Microvascular sensitivity to endothelin-1 was decreased in the DOCA-salt group. In the presence of an endothelin type A (ET-A) receptor antagonist, low concentrations of endothelin-1 induced a significant vasoconstriction in the DOCA-salt group. In the presence of endothelin type B (ET-B) receptor antagonist, microvascular responses to endothelin-1 were attenuated in the DOCA-salt group. These results indicated that the increased tissue level of endothelin-1 may decrease the ET-A receptor-mediated vascular response to endothelin-1. However, the ET-B receptor-mediated vasoconstriction is potentiated during DOCA-salt hypertension.

Topics: Animals; Aorta, Thoracic; Desoxycorticosterone; Dose-Response Relationship, Drug; Endothelin Receptor Antagonists; Endothelin-1; Hypertension; Male; Microcirculation; Muscle, Skeletal; Oligopeptides; Peptides, Cyclic; Piperidines; Rats; Rats, Sprague-Dawley; Receptor, Endothelin A; Receptor, Endothelin B; Sodium Chloride

Regulation mechanisms of the activity of vascular mitogen-activated protein (MAP) kinases, enzymes believed to be involved in the pathway for cell proliferation, may be altered in hypertension. To examine whether vascular MAP kinase activation mechanisms are altered in hypertension, we measured the activity of MAP kinases in rat aorta strips from spontaneously hypertensive rats (SHR) and from deoxycorticosterone acetate (DOCA)-salt hypertensive rats, and examined whether vascular angiotensin and endothelin systems are responsible for the alteration of MAP kinase activation in these hypertensive models. Endothelium-denuded aorta strips were incubated at 37 degrees C in medium. MAP kinase activity after incubation was increased in rat aorta strips. The MAP kinase activation was greater in 9- and 15-week-old SHR aorta strips than in age-matched Wistar Kyoto rats (WKY) aorta strips. Similarly, MAP kinase activation was enhanced in aorta strips from DOCA-salt hypertensive rats. In aorta strips from these kinds of rats, the angiotensin receptor antagonist, losartan, and the endothelin receptor antagonist, cyclo (D-alpha-aspartyl-L-prolyl-D-valyl-L-leucyl-D-tryptophyl) (BQ123), inhibited the MAP kinase activation. The losartan-induced, but not BQ123-induced, inhibition of MAP kinase activation was enhanced in 15-week-old SHR aorta strips, whereas the BQ123-induced, but not losartan-induced, inhibition of MAP kinase activation was enhanced in DOCA-salt hypertensive rat aorta strips. Angiotensin II-induced MAP kinase activation was enhanced in 15-week-old SHR aorta strips, whereas it was depressed in DOCA-salt hypertensive rat aorta strips. These results indicate that MAP kinase activation function is enhanced in aorta strips from both kinds of hypertensive rats. It appears that the enhancement of MAP kinase activation results partly from enhanced vascular angiotensin system in SHR and from enhanced vascular endothelin system in DOCA-salt hypertensive rats.

Topics: Angiotensin II; Angiotensin Receptor Antagonists; Animals; Antihypertensive Agents; Desoxycorticosterone; Endothelin Receptor Antagonists; Endothelin-1; Endothelium, Vascular; Enzyme Activation; Hypertension; In Vitro Techniques; Losartan; Male; Mitogen-Activated Protein Kinases; Muscle, Smooth, Vascular; Peptides, Cyclic; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Rats, Wistar; Receptor, Angiotensin, Type 1; Receptor, Angiotensin, Type 2; Receptors, Angiotensin; Receptors, Endothelin; Sodium Chloride; Vasoconstrictor Agents

Homozygous knock-out of ET(A) or ET(B) receptor genes results in lethal developmental phenotypes in the mouse. Such deleterious phenotypes do not occur in heterozygous littermates. However, it remains to be determined whether mice partially defective in ET(A) or ET(B) receptors display significant alterations in their responses to exogenous or endogenous endothelin-1 (ET-1). Furthermore, the anesthetized ET(B) (+/-) knock-out mice showed a significantly higher mean arterial blood pressure than the ET(A) (+/-) knock-out or their wild-type littermates. The pressor response to ET-1 but not to a selective ET(B) agonist, IRL-1620, was significantly reduced in the ET(A) (+/-) knock-out mice. In ET(B) (+/-) knock-out mice, the pressor effect of IRL-1620 was more markedly altered than those induced by ET-1. In wild-type mice, both ET(A) and ET(B) receptors were found to be involved in the pressor effect of ET-1, as confirmed by the significant and specific antagonism induced by either BQ-123 (ET(A) antagonist) or BQ-788 (ET(B) antagonist). Also, ET(A)-selective or mixed ET(A)/ET(B)- but not ET(B)-selective antagonists reversed the hypertensive state of the ET(B) (+/-) knock-out mice to the level of wild-type littermates. Finally, radiolabeled ET-1 plasmatic clearance was altered in ET(B) (+/-) but not ET(A) (+/-) knock-out mice when compared with wild-type animals. Thus, heterozygous knock-out of ET(B) receptors results in a hypertensive state, suggesting an important physiological role for that particular receptorial entity in opposing the endogenous ET-1-dependent pressor effects in the mouse.

Topics: Animals; Antihypertensive Agents; Blood Pressure; Drug Interactions; Endothelin Receptor Antagonists; Endothelin-1; Endothelins; Female; Heterozygote; Hypertension; Indans; Iodine Radioisotopes; Male; Metabolic Clearance Rate; Mice; Mice, Inbred C57BL; Mice, Knockout; Mitogen-Activated Protein Kinases; Oligopeptides; Peptide Fragments; Peptides, Cyclic; Piperidines; Receptor, Endothelin A; Receptor, Endothelin B; Receptors, Endothelin

We investigated the possible role of endothelin in the increased vasoconstrictor tone of hypertensive patients using antagonists of endothelin receptors. Forearm blood flow (FBF) responses (strain-gauge plethysmography) to intraarterial infusion of blockers of endothelin-A (ETA) (BQ-123) and endothelin-B (ETB) (BQ-788) receptors, separately and in combination, were measured in hypertensive patients and normotensive control subjects. In healthy subjects, BQ-123 alone or in combination with BQ-788 did not significantly modify FBF (P=0.78 and P=0.63, respectively). In hypertensive patients, in contrast, BQ-123 increased FBF by 33+/-7% (P<0.001 versus baseline), and the combination of BQ-123 and BQ-788 resulted in a greater vasodilator response (63+/-12%; P=0.006 versus BQ-123 alone in the same subjects). BQ-788 produced a divergent vasoactive effect in the two groups, with a decrease of FBF (17+/-5%; P=0.004 versus baseline) in control subjects and transient vasodilation (15+/-7% after 20 minutes) in hypertensive patients (P<0.001, hypertensives versus controls). The vasoconstrictor response to endothelin-1 was slightly higher (P=0.04) in hypertensive patients (46+/-4%) than in control subjects (32+/-4%). Our data indicate that patients with essential hypertension have increased vascular endothelin activity, which may be of pathophysiological relevance to their increased vascular tone. In these patients, nonselective ETA and ETB blockade seems to produce a greater vasodilator effect than selective ETA blockade.

Topics: Endothelin-1; Endothelin-2; Female; Forearm; Humans; Hypertension; Male; Middle Aged; Oligopeptides; Peptides, Cyclic; Piperidines; Regional Blood Flow; Vasodilation

We previously demonstrated that endothelin-1 (ET-1) increases the neuronal activity of neurons in the nucleus tractus solitarii (NTS) and augments the response to glutamate (Glu), using in vitro brainstem slice preparations of normotensive Wistar-Kyoto (WKY) rats. This study was designed to determine whether the effects of ET-1 on neuronal activity and synaptic transmission in the NTS are altered in spontaneously hypertensive rats (SHR). Experiments were performed with WKY rats and age-matched SHR. We recorded the extracellular single unit of neuronal activity of NTS neurons in response to electrical stimulation of the solitary tracts using in vitro brainstem slice preparations. ET-1 or Glu was iontophoretically applied to the recording neurons. ET-1 increased the neuronal activity of NTS neurons in SHR as well as WKY. The magnitude of the increase in the neuronal activity evoked by Glu was augmented by application of ET-1 in WKY rats (6.1 +/- 0.6 to 11.1 +/- 1.7 spikes/s, p < 0.05) but not in SHR (5.6 +/- 0.5 to 5.6 +/- 0.6 spikes/s). These results indicate that ET-1 increases the neuronal activity of the NTS in both SHR and WKY. However, the increase in neuronal activity in response to Glu is augmented by ET-1 in WKY but not in SHR, suggesting that reflex control is impaired in SHR.

Topics: Animals; Antihypertensive Agents; Blood Pressure; Electric Stimulation; Endothelin Receptor Antagonists; Endothelin-1; Glutamic Acid; Heart Rate; Hypertension; In Vitro Techniques; Iontophoresis; Male; Microelectrodes; Neurons; Peptides, Cyclic; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Receptor, Endothelin A; Signal Transduction; Solitary Nucleus; Synaptic Transmission

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

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

Intracerebroventricular injections of endothelin-1 (ET-1) are reported to cause dose-related increases in sympathetic nerve activity and blood pressure in anesthetized normotensive rats. These studies were performed to determine the following: which endothelin receptor, A or B, is involved in mediating sympathetic and cardiovascular effects of ET-1 injected centrally; whether central endothelin tonically participates in blood pressure regulation in normotensive rats; and whether the altered endothelin system in the central nervous system contributes to blood pressure elevation in hypertensive rats. ET-1, ET-A antagonist (BQ-123), or ET-B antagonist (RES-701-1) was injected into the lateral cerebral ventricle (i.c.v.) of urethane-anesthetized normotensive Wistar and Wistar-Kyoto (WKY) rats, spontaneously hypertensive rats (SHRs), and stroke-prone SHRs (SHR-SPs). In Wistar rats, i.c.v. injections of ET-1 (1, 5, 10 pmol) consistently increased sympathetic nerve activity, thereby elevating blood pressure in a dose-related manner. The pressor responses induced by i.c.v. ET-1 were abolished after intravenous pretreatment with phentolamine. Neither ET-A nor ET-B antagonist, when injected centrally, altered basal levels of sympathetic nerve activity, heart rate, or blood pressure in Wistar rats. However, sympathetic activation and pressor responses induced by i.c.v. injection of endothelin were completely abolished after i.c.v. pretreatment with ET-A antagonist but were unaffected after pretreatment with ET-B antagonist. Although i.c.v. injections of ET-1 increased sympathetic nerve activity and blood pressure in WKY rats, SHRs, and SHR-SPs, the magnitudes of these responses did not differ among these three groups. In contrast, i.c.v. injections of ET-A antagonist decreased sympathetic nerve activity, blood pressure, and heart rate only in SHR-SPs, but not in WKY rats and SHRs. In addition, the depressor effects of i.c.v. ET-A antagonist in SHR-SPs were ascertained while these rats were awake. In summary, i.c.v. injections of ET-1 increased sympathetic nerve activity and blood pressure via ET-A receptors but not via ET-B receptors. Central ET might tonically activate sympathetic nerve activity to thereby contribute to blood pressure elevation in SHR-SPs, but not in WKY rats and SHRs.

Topics: Anesthesia; Animals; Antihypertensive Agents; Blood Pressure; Brain; Endothelins; Heart Rate; Hypertension; Injections, Intraventricular; Male; Peptides, Cyclic; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Rats, Wistar; Receptors, Endothelin; Sympathetic Nervous System

The vascular structural remodeling function may be altered in genetically hypertensive animals, spontaneously hypertensive rats (SHR). To examine this possibility, we measured the activity of mitogen-activated protein (MAP) kinases, enzymes believed to be involved in the pathway for cell proliferation, in rat aorta strips, and examined whether the endothelium removal-induced MAP kinase activation function is altered in SHR and whether vascular angiotensin and endothelin systems are responsible for the alteration of MAP kinase activation in SHR. Male 4-week-old SHR and age-matched Wistar Kyoto rats (WKY) supplied by Charles River Japan were used. Endothelium-denuded aorta strips were incubated at 37 degrees C in medium. MAP kinase activity after incubation was time-dependently increased in strips from SHR and WKY. MAP kinase activation was greater in SHR than in WKY aorta strips. Similarly, MAP kinase activation was enhanced in aorta strips from 4-week-old SHR and stroke prone SHR supplied by the Diseases Model Cooperative Research Association (Kyoto, Japan). In aorta strips from SHR and WKY, the angiotensin receptor antagonist, losartan, and the endothelin receptor antagonist, cyclo (D-alpha-aspartyl-L-prolyl-D-valyl-L-leucyl-D-tryptophyl)(BQ123), caused concentration-dependent inhibition of MAP kinase activation. The losartan-induced but not BQ123-induced inhibition of MAP kinase activation was greater in SHR than in WKY aorta strips. Angiotensin II caused a concentration-dependent increase in MAP kinase activity and the angiotensin II-induced MAP kinase activation was greater in SHR than in WKY aorta strips. These results indicate that endothelium removal-induced MAP kinase activation is enhanced in aorta strips from young SHR, suggesting that vascular structural remodeling function may be enhanced in SHR. It appears that the enhancement of MAP kinase activation results, at least in part, from enhanced function of vascular angiotensin system in SHR.

Topics: Angiotensin II; Animals; Antihypertensive Agents; Aorta; Calcium-Calmodulin-Dependent Protein Kinases; Endothelin-1; Endothelium, Vascular; Enzyme Activation; Hypertension; Losartan; Male; Peptides, Cyclic; Rats; Rats, Inbred SHR; Rats, Inbred WKY

Endothelin (ET)-1 has been implicated as a critical mediator in the pathogenesis of hypoxic pulmonary hypertension. We questioned whether, during exposure to chronic hypobaric hypoxia, rat pulmonary artery smooth muscle cells (PASMC) became sensitized to ET-1. Two effects of ET-1, inhibition of voltage-gated K(+) (K(v)) channels and release of intracellular Ca(2+), were studied using whole cell patch clamp and single cell indo 1 fluorescence, respectively. In both normotensive and chronically hypoxic-hypertensive PASMC, ET-1 caused concentration-dependent inhibition of voltage-gated K(+) current [I(K(v))], with maximum inhibition of 12-18% seen at a concentration of 0.1-1 nM. Although the chronically hypoxic-hypertensive PASMC was no more susceptible to ET-1-mediated I(K(v)) inhibition, a switch in coupling between ET-1 and I(K(v)) from ET(B) to ET(A) receptors occurred. This switch in receptor coupling, combined with reduced I(K(v)) density and increased ET-1 production in the hypoxic rat lung, may help explain the ability of ET(A)-receptor blockers to attenuate the development of hypoxic pulmonary hypertension in vivo.

Topics: Animals; Antihypertensive Agents; Calcium; Chronic Disease; Electrophysiology; Endothelin Receptor Antagonists; Endothelin-1; Hypertension; Hypoxia; Male; Muscle, Smooth, Vascular; Oligopeptides; Peptides, Cyclic; Piperidines; Potassium Channel Blockers; Potassium Channels; Pulmonary Artery; Rats; Rats, Sprague-Dawley; Receptor, Endothelin A; Receptors, Endothelin

We attempted to determine the role of endothelin in a previously characterized animal model of preeclampsia by studying the effect of a specific endothelin antagonist, BQ123, on blood pressure.. A preeclampsia-like condition was induced by infusing pregnant rats with the nitric oxide synthase inhibitor N(G)-nitro-L -arginine methyl ester. Osmotic minipumps were inserted subcutaneously into timed pregnant Harlan-Sprague-Dawley rats on day 17 of pregnancy (term, 22 days). The pumps were loaded to continuously deliver either vehicle (control group) or N(G)-nitro-L -arginine methyl ester 50 mg/d, either alone or with BQ123 at 0.5 mg/d. In a similar but separate experiment, the dose of BQ123 was increased to 1 mg/d. Blood pressure was measured with the tail-cuff method before pump insertion and then daily until postpartum day 2.. Except for a decrease on the day after pump insertion, BQ123 0.5 mg/d had no significant effect on the hypertension induced by N(G)-nitro-L -arginine methyl ester. At the higher dose, however, BQ123 significantly attenuated the increase in blood pressure induced by N(G)-nitro-L -arginine methyl ester during most of the study period.. The effect of nitric oxide inhibition can be successfully attenuated by the use of an endothelin antagonist, thereby supporting the role of endothelin in the hypertension described with the preeclampsialike condition seen in pregnant rats.

Topics: Animals; Blood Pressure; Disease Models, Animal; Endothelins; Enzyme Inhibitors; Female; Gestational Age; Hypertension; NG-Nitroarginine Methyl Ester; Nitric Oxide Synthase; Peptides, Cyclic; Pre-Eclampsia; Pregnancy; Rats; Rats, Sprague-Dawley

Angiotensin-converting enzyme (ACE) inhibition alone or in combination with the angiotensin type-I receptor (AT1) antagonist losartan augments circulating levels of the bioactive peptide angiotensin-(1-7) [Ang-(1-7)]. Hence, we determined whether Ang-(1-7) contributes to the hypotensive effects produced by the combined administration of lisinopril and losartan in spontaneously hypertensive rats by blocking the peptide's synthesis with either of two structurally different neprilysin inhibitors. Intravenous administration of CGS 24592 (30 mg/kg) to rats in which blood pressure was normalized by 9 days of therapy with lisinopril and losartan elicited an elevation of mean arterial pressure that was sustained throughout the infusion period and for 20 minutes thereafter. The hypertensive response was associated with a 62% reduction in circulating levels of Ang-(1-7) and no change in plasma angiotensin II (Ang II). Intravenous infusion of one other neprilysin inhibitor (SCH 39370, 30 mg/kg) produced an increase in mean blood pressure of a magnitude similar to that found with CGS 24592. Pretreatment with the nonselective antagonist [Sar1,Thr8]-Ang II abolished any additional pressor effects of either neprilysin inhibitor in spontaneously hypertensive rats treated with lisinopril or losartan. However, neither the endothelin A antagonist BQ123 nor the kinin B2 antagonist HOE 140 had an effect on basal blood pressure or altered the pressor or heart rate effects of the neprilysin inhibitors. These data suggest that inhibition of Ang-(1-7) formation in rats exposed to the combined blockade of Ang II production and activity is associated with a reversal of the antihypertensive actions produced by these therapies. Thus, endogenous Ang-(1-7) functions as a vasodilator hormone in this form of genetic hypertension.

Topics: Angiotensin I; Angiotensin II; Animals; Antihypertensive Agents; Blood Pressure; Bradykinin; Dipeptides; Heart Rate; Hypertension; Kinetics; Lisinopril; Losartan; Male; Neprilysin; Organophosphonates; Peptide Fragments; Peptides, Cyclic; Phenylalanine; Protease Inhibitors; Rats; Rats, Inbred SHR; Renin-Angiotensin System

The effects of endothelium-related substances such as acetylcholine, a stimulator of endogenous NO-production, the NO-synthesis inhibitor L-NMMA, the exogenous NO-donor sodium nitroprusside and the endothelin (ET)A-receptor antagonist BQ123, on uveal blood flow were investigated in normotensive and hypertensive SHR rats.. The radioactively-labelled microsphere method was applied for the measurement of regional blood flow in the uvea.. Under resting conditions, local blood flow was lower in the hypertensive animals. The increase in choroidal blood flow (145 +/- 50%; P < 0.01) and reduction in vascular resistance (-58 +/- 7%; P < 0.01) observed in the WKY after i.v. infusion of acetylcholine, 2 micrograms x kg bw-1 x min-1, were significantly less pronounced in animals pretreated with L-NMMA, indicating local formation of NO as a vasodilator mechanism. In contrast, acetylcholine did not induce significant vasodilation in the choroid of SHR rats. In the anterior uvea of both strains, acetylcholine did not affect local blood flow. L-NMMA, 20 mg x kg bw-1, alone reduced blood flow in the entire uvea of both strains. Intravenous injection of BQ123, 1 mg x kg bw-1, did not affect regional blood flow in the uvea of WKY or SHR animals. Infusion of acetylcholine following ETA-receptor blockade induced vasodilation in both the choroid and anterior uvea in the WKY but not in the SHR.. Acetylcholine-stimulated NO-mediated vasodilation, but not basal NO-formation, was impaired in the choroid of the SHR. Furthermore, an interaction between vasoconstricting ET and acetylcholine was found in the anterior uvea of normotensive but not hypertensive rats.

Topics: Acetylcholine; Animals; Endothelin Receptor Antagonists; Endothelium, Vascular; Enzyme Inhibitors; Hypertension; Male; Microspheres; Nitric Oxide; Nitroprusside; omega-N-Methylarginine; Peptides, Cyclic; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Regional Blood Flow; Uvea; Vascular Resistance; Vasodilation

1. The objectives of the present study were to study regional differences in haemodynamics between spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) rats induced by the nitric oxide synthase (NOS) inhibitor NG-monomethyl-L-arginine (L-NMMA) and the endothelin ETA receptor antagonist BQ 123 in vivo in tissues known to be important for blood pressure (BP) regulation (heart, kidney and skeletal muscle). Furthermore, the effect of acetylcholine (ACh) infusion (2 micrograms/kg per min) was examined after L-NMMA or BQ 123. The microsphere method was used for determinations of cardiac index (CI) and regional haemodynamics. 2. NG-Monomethyl-L-arginine (20 mg/kg) increased BP (26-48%; P < 0.01) and reduced CI in both rat strains. BQ 123 (1 mg/kg) reduced BP slightly (-4 to 11%; P < 0.05). 3. NG-Monomethyl-L-arginine significantly increased myocardial and skeletal muscle vascular resistance in SHR only; however, in the kidney, L-NMMA reduced blood flow and increased vascular resistance in both rat strains. 4. BQ 123 induced minor changes in regional haemodynamics that were not significantly different between the two strains. 5. Acetylcholine following BQ 123 induced an increase in myocardial blood flow in WKY rats, but decreased blood flow in SHR. Acetylcholine following L-NMMA reduced myocardial blood flow in both strains. 6. Acetylcholine following BQ 123 induced renal vasodilation in WKY rats but, following L-NMMA, ACh did not induce renal vasodilation in either rat strain. In contrast, L-NMMA did not abolish the vasodilation of acetylcholine in skeletal muscle in WKY rats. 7. In conclusion, the contribution of nitric oxide to basal vessel tone was not impaired in the heart, skeletal muscle and kidney in SHR. Antagonism of ETA receptors caused similar haemodynamic responses in both rat strains in these organs. Furthermore, NOS inhibition, but not ETA blockade, blunted the expected ACh-induced vasodilation in the heart and kidney in WKY rats, but not in skeletal muscle in both strains.

Topics: Acetylcholine; Animals; Blood Pressure; Coronary Vessels; Endothelin Receptor Antagonists; Enzyme Inhibitors; Hemodynamics; Hydrogen-Ion Concentration; Hypertension; Male; Muscle, Skeletal; Nitric Oxide Synthase; omega-N-Methylarginine; Peptides, Cyclic; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Regional Blood Flow; Renal Circulation; Vasodilator Agents

Effects of the endothelin receptor type A antagonist BQ 123 and the NO synthase inhibitor L-NMMA on cerebral blood flow were studied in vivo in anaesthetized hypertensive (SHR) and normotensive (WKY) rats. The effects of acetylcholine following pre-treatment with these drugs were also studied with the microsphere method for blood flow determination in the cortex, thalamus, caudatus, pons, medulla, cerebellum and hypophysis. BQ 123 (1 mg kg-1) induced only minor effects on cerebral blood flow in both strains (n = 8), whereas L-NMMA (N = 8; 20 mg kg-1) reduced regional cerebral blood flow significantly in most regions (21-54%) in the hypertensive, but not in the normotensive rat. In normotensive rats pre-treated with BQ 123 intravenous administration of acetylcholine (2 micrograms kg-1 min-1) induced a widespread significant increase (20-50%) in cerebral blood flow despite a reduction of the mean arterial blood pressure, while no significant effects were seen in hypertensive animals. Intravenous infusion of acetylcholine in animals pre-treated with L-NMMA did not affect cerebral blood flow in most regions in either of the two rat strains. In conclusion, a vasodilatory response to acetylcholine was found following endothelin receptor A antagonism in the WKY rat only, suggesting a role for endothelin in the control of cerebral blood flow in this strain. Furthermore, a higher basal vasodilating nitric oxide-tone seems to be present in the hypertensive rat compared with the normotensive rat.

Topics: Acetylcholine; Animals; Blood Flow Velocity; Blood Pressure; Brain Chemistry; Cerebral Arteries; Cerebrovascular Circulation; Endothelin Receptor Antagonists; Endothelium, Vascular; Enzyme Inhibitors; Hypertension; Male; Nitric Oxide Synthase; omega-N-Methylarginine; Peptides, Cyclic; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Receptor, Endothelin A

Cyclosporine A (CsA) is an immunosuppressive agent that also causes hypertension. The effect of CsA on vascular responses was determined in Sprague-Dawley rats and isolated rat aortic rings. Male rats weighing 250 to 300 g were given either CsA (25 mg. kg-1. d-1) in olive oil or vehicle by intraperitoneal injection for 7 days. CsA administration produced a 42% increase (P<0.001) in mean arterial pressure (MAP) that reached a plateau after 3 days. Conversely, the levels of both nitrate/nitrite, metabolites of nitric oxide (NO), and cGMP, which mediates NO action, decreased by 50% (P<0.001) and 35% (P<0.001), respectively, in the urine. Thoracic aortic rings from rats treated with CsA and precontracted with endothelin (10(-9) mol/L) showed a 35% increase (P<0.001) in tension, whereas endothelium-dependent relaxation induced by acetylcholine (ACh, 10(-9) mol/L) was inhibited 65% (P<0.001) compared with that in untreated rats. This response was similar to that of endothelium-denuded aortic rings from untreated rats in which ACh-induced relaxation was completely abolished (P<0.001), but relaxation induced by S-nitroso-N-acetylpenicillamine (SNAP, 10(-8) mol/L) was unaffected (P<0.001). ACh-induced formation of both nitrate/nitrite and cGMP by both denuded and CsA-treated aortic rings was inhibited 95% (P<0.001) and 65% (P<0.001), respectively, compared with intact aortic rings. The effects of CsA were reversed both in vivo and in vitro by pretreatment with L-arginine (10 mg. kg-1. d-1 IP), the precursor of NO. There were no changes in MAP and tension in rats treated with L-arginine alone. In summary, CsA inhibits endothelial NO activity, with resulting increases in MAP and tension, and this inhibition can be overcome by parenteral administration of L-arginine.

Topics: Animals; Aorta; Arginine; Blood Pressure; Bosentan; Cyclic GMP; Cyclosporine; Endothelin Receptor Antagonists; Enzyme Inhibitors; Hypertension; Immunosuppressive Agents; Male; Nitrates; Nitrites; Olive Oil; Penicillamine; Peptides, Cyclic; Plant Oils; Rats; Rats, Sprague-Dawley; Sulfonamides; Vasoconstriction

Endothelin (ET) receptors, ET-1-like immunoreactivity and nitric oxide synthase (NOS) were examined in the brain of stroke-prone spontaneously hypertensive rats (SHRSPs) with cerebral apoplexy. Our receptor autoradiographic method with 125I-ET-1 and unlabeled selective ligands for ET receptors revealed de novo expressions of ET(A) and ET(B) receptors in areas of neural lesions with cerebrovascular damage in SHRSPs. Immunohistochemical staining for ET-1 showed clear ET-1-like immunoreactivity in areas with highly expressed ET receptors. Histochemical studies on astrocytes and microglia suggested that these glial cells, aggregating in lesions, may carry ET receptors, ET-1-like immunoreactivity. Furthermore, NOS detected histochemically using an NADPH-diaphorase staining method was rich on glial cells in damaged areas of the brain in SHRSPs with cerebral apoplexy. Our data suggest the pathophysiological significance of glial ET(A) and ET(B) receptors, ET-1 and NOS in neural lesions of SHRSPs.

Topics: Animals; Autoradiography; Binding Sites; Brain; Cerebrovascular Disorders; Disease Susceptibility; Endothelin Receptor Antagonists; Endothelin-1; Endothelins; Hypertension; NADPH Dehydrogenase; Nitric Oxide Synthase; Peptide Fragments; Peptides, Cyclic; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Receptors, Endothelin

To investigate the role of the endothelium in the functional interaction between endothelin-1 and norepinephrine in the contractile response of aortas from Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR).. Thoracic aorta rings with and without endothelium from SHR and from WKY rats were suspended in an organ bath to record the isometric tension. After an equilibration period of 120 min, the preparations with and without endothelin-1 were subjected to single and cumulative additions of norepinephrine in different experiments. To characterize the mechanisms involved in the interaction between endothelin-1 and norepinephrine, the aortic rings were pretreated with a cyclooxygenase pathway inhibitor (piroxicam, SO29548), an inhibitor of NO synthase [NG-nitro-L-arginine (NLA)], or selective endothelin receptor blockers (BQ-123 or BQ-788). In some experiments we examined the contractile responses to norepinephrine in aortas pretreated either with angiotensin II (AII) or with U46619, an agonist of prostaglandin H2-thromboxane A2 receptors. Finally, we examined the effect of the combination of calcium-entry blockade by administration of nifedipine and treatment with either endothelin-1 or U46619 on the norepinephrine reactivity.. Administration of 3 x 10(-10) mol/l endothelin-1 potentiated the contractile response to norepinephrine in SHR aortas with endothelium, irrespective of whether they had been treated with NLA. No endothelin-1-mediated enhancement of the response to norepinephrine was observed in SHR denuded rings and in untreated and NLA-treated WKY rat aortas. All did not affect the response to norepinephrine in SHR rings with endothelium. The amplification by endothelin-1 of the response to (1-100) x 10(-9) mol/l norepinephrine was abolished by blockade of the cyclooxygenase pathway with piroxicam or SO29548. In WKY rat and SHR denuded aortas, 10(-8) mol/l U46619 potentiated the contractile responses to norepinephrine. Administration of 3 x 10(-6) mol/l BQ-123 abolished the increase in reactivity to norepinephrine evoked by endothelin-1 in intact SHR aorta, whereas 3 x 10(-6) mol/l BQ-788 failed to modify this potentiating effect. Administration of 10(-8) mol/l nifedipine inhibited the potentiation of the norepinephrine-induced contractions evoked both by endothelin-1 in SHR aortic rings with endothelium and by U46619 in SHR denuded rings.. Our results show that a low concentration of endothelin-1 induced potentiation of the contractile response to norepinephrine in SHR aortas but not in WKY rat aortas. This response was endothelium-dependent. Furthermore, our study affords functional arguments that both endothelial and smooth muscle pathways are involved in the potentiating interaction. We propose that endothelin-1 stimulates the production of endothelium- and cyclooxygenase-generated vasoconstrictor factors, which in turn may serve directly as priming stimuli at the vascular smooth muscle level, to activate the Ca(2+)-signal pathway and consequently to increase locally the vascular sensitivity to norepinephrine.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Animals; Aorta, Thoracic; Bridged Bicyclo Compounds, Heterocyclic; Cyclooxygenase Inhibitors; Drug Synergism; Endothelin Receptor Antagonists; Endothelin-1; Endothelium, Vascular; Fatty Acids, Unsaturated; Hydrazines; Hypertension; Male; Nifedipine; Norepinephrine; Oligopeptides; Peptides, Cyclic; Piperidines; Piroxicam; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Receptors, Endothelin; Vasoconstriction; Vasoconstrictor Agents; Vasodilator Agents

We used Ro 46-8443, non-peptidic antagonist selective of endothelin ETB receptors, to study the role of ETB receptors in rat hypertension models. In normotensive rats, Ro 46-8443 decreased blood pressure, but in SHR and DOCA rats, it induced a pressor effect, due to blockade of ETB-mediated release of nitric oxide since L-NAME prevented it. In rats rendered hypertensive by chronic L-NAME, Ro 46-8443 did not induce a pressor but depressor effect. Thus, in DOCA rats and SHR, Ro 46-8443 reveals a predominant influence of endothelial 'vasorelaxant' ETB receptors, while in normotensive rats the prevailing role of ETB receptors seems to be in mediating a vasoconstrictor tone.

Topics: Animals; Arginine; Blood Pressure; Endothelin Receptor Antagonists; Hypertension; NG-Nitroarginine Methyl Ester; Nitric Oxide Synthase; Peptides, Cyclic; Pyrimidines; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Receptor, Endothelin B; Receptors, Endothelin; Sulfonamides; Viper Venoms

The renal endothelin system has been implicated in the development and maintenance of hypertension in spontaneously hypertensive rats (SHR). However, little is known about the function and cellular distribution of endothelin receptor subtypes in the kidneys of SHR.. We analyzed the expression of endothelin receptor subtypes in the kidneys of 16-week-old SHR using Scatchard analysis, receptor autoradiography, Northern blot analysis and in situ hybridization. Wistar-Kyoto rats (WKY) served as controls. Furthermore, we investigated the effects of the mixed (A/B) endothelin receptor antagonist bosentan and the ETA receptor antagonist BQ 123 on mean arterial blood pressure (MAP), renal blood flow (RBF) and glomerular filtration rate (GFR) in conscious chronically instrumented rats.. In SHR, we found by receptor autoradiography an overexpression of the endothelin A receptor (ETA) in the glomeruli (2.2 +/- 0.4-fold; P < 0.05) and smooth muscle cells of intrarenal arteries (1.9 +/- 0.2-fold; P < 0.05) compared to age-matched WKY. In addition, our study revealed a pronounced upregulation of endothelin B receptor (ETB) in the glomeruli of SHR (5.6 +/- 0.8-fold; P < 0.01). Blockade of endothelin receptors in SHR with bosentan (A and B receptor blockade) as well as with BQ 123 (A receptor blockade) led to a significant decrease in MAP (-18.6 +/- 2.1 and -19 +/- 1.3 mmHg, respectively; P < 0.05 in both cases) and a significant increase in RBF (+2.8 +/- 0.5 and +3.1 +/- 0.37 ml/min, respectively; P < 0.05 in both cases). The blockade of both ETA and ETB by bosentan had no further effect on MAP reduction or RBF increase in SHR compared to the ETA blockade by BQ 123. The ETA antagonist BQ 123 had no effect on GFR either in SHR or in WKY, whereas the combined blockade of ETA and ETB by bosentan significantly decreased GFR in SHR by about 50% but not in WKY.. Our data demonstrated a correlation between the overexpression of vascular ETA receptors and the pronounced upregulation of glomerular ETB receptors in the kidneys of SHR and their impact on the regulation of renal blood flow, glomerular filtration rate and blood pressure in these animals.

Topics: Animals; Autoradiography; Blood Pressure; Blotting, Northern; Bosentan; Endothelin Receptor Antagonists; Glomerular Filtration Rate; Hypertension; In Situ Hybridization; Kidney; Kidney Glomerulus; Male; Muscle, Smooth, Vascular; Peptides, Cyclic; Protein Binding; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Receptors, Endothelin; Renal Circulation; RNA, Messenger; Sulfonamides; Up-Regulation

Bosentan is a nonspecific antagonist for endothelin (ET) receptors, and BQ123 is a specific inhibitor for ET-A receptors. We compared the effects of bosentan (10 mg/kg intravenously, i.v.) and BQ123 (10 mg/kg/h i.v.) on blood pressure and renal function in deoxycorticosterone acetate (DOCA)-salt rats, Dahl salt-sensitive (Dahl-S) rats, and normotensive Wistar rats. In normotensive Wistar rats, bosentan and BQ123 decreased blood pressure. Only BQ123 decreased glomerular filtration rate (GFR) and filtration fraction. These results indicate that ET-A receptors play a role in glomerular function. In DOCA-salt rats, bosentan and BQ123 caused a decrease in blood pressure to normal range and a decrease in renal vascular resistances. Bosentan decreased filtration fraction. Paradoxically, BQ123 caused a decrease in GFR. In Dahl-S rats, bosentan and BQ123 decreased blood pressure, but blood pressure did not reach normal ranges. Bosentan did not modify renal function, but BQ123 caused a decrease in the GFR and filtration fraction. Our results confirm the importance of specific and nonspecific ET antagonists in decreasing blood pressure in models of salt-dependent hypertension. However nonspecific inhibition of ET action did not improve renal function and specific inhibition of ET-A receptors by BQ123 temporarily worsened renal function.

Topics: Animals; Blood Pressure; Bosentan; Desoxycorticosterone; Endothelins; Glomerular Filtration Rate; Hypertension; Peptides, Cyclic; Rats; Rats, Wistar; Renal Circulation; Renal Insufficiency; Sodium Chloride; Sulfonamides

Both glucocorticoids and mineralocorticoids are involved in circulatory homoeostasis and blood pressure control. In recent years direct effects of both steroid classes on vascular smooth muscle cells (VSMC) have been reported. We have thus examined the effects of RU 28362, a pure glucocorticoid agonist, and aldosterone, the physiologic mineralocorticoid, on the binding to VSMC from spontaneously hypertensive rats (SHR) of two key vasoactive peptides, endothelin-1 and angiotensin II. Binding of angiotensin II rose, and that of endothelin-1 declined, in a time- and dose-dependent fashion with maximal effects observed at 24 h and half-maximal effects for each at 2-3 nM RU 28362. Scatchard analysis showed that for both endothelin-1 and angiotensin II, RU 28362 alters receptor number but not affinity; competition studies with receptor-selective ligands (BQ123, S6C, DuP753 and PD123319) show that glucocorticoids specifically elevate (X2) AT-1 receptors and specifically lower (to approximately 30%) levels of ETA receptors. Treatment of VSMC with the antiglucocorticoid RU 38486 reversed the effect of glucocorticoids on endothelin-1 and angiotensin II binding, confirming the Type II (glucocorticoid) receptor mediated effect of the glucocorticoids. Aldosterone (100 nM) also lowers endothelin-1 binding and increases angiotensin II binding in VSMC; that this effect reflects aldosterone occupancy of classical glucocorticoid receptors is shown by the blockade of the aldosterone effect by an equal concentration (100 nM) of RU 38486--i.e. there is no evidence for an action of aldosterone via mineralocorticoid receptors. We interpret our results as evidence for a complex modulation of receptors for vasoactive peptides in VSMC by glucocorticoid but not mineralocorticoid hormones.

Topics: Aldosterone; Androstanols; Angiotensin II; Angiotensin Receptor Antagonists; Animals; Biphenyl Compounds; Cells, Cultured; Endothelin Receptor Antagonists; Endothelins; Glucocorticoids; Hypertension; Imidazoles; Losartan; Male; Mifepristone; Muscle, Smooth, Vascular; Peptides, Cyclic; Rats; Rats, Inbred SHR; Receptor, Endothelin A; Receptor, Endothelin B; Receptors, Endothelin; Receptors, Glucocorticoid; Receptors, Mineralocorticoid; Tetrazoles; Viper Venoms

Stimulation of endothelin subtype B (ETB) receptors has been proposed to induce release of endothelium-derived nitric oxide (EDNO).. To obtain direct evidence of its release and its alteration in deoxycorticosterone acetate (DOCA)-salt hypertension, EDNO released from renal vessels by ET stimulation was assayed by a highly sensitive chemiluminescence method. Kidneys were isolated from DOCA-salt and control rats, and renal perfusion pressure (RPP) and EDNO (by hydrogen peroxide-luminol chemiluminescence) in the perfusate were monitored simultaneously during perfusion of ET-1, ET-3, an ETA receptor antagonist (BQ-123), and an ETB receptor agonist (BQ-3020). In control rats, ET-1 and ET-3 dose-dependently increased both RPP and NO release. Although the vasoconstricting effects of ET-1 were greater, their NO-releasing effects were comparable. The increase in NO release by ETs was inhibited by NG-monomethyl-L-arginine. After 10(-6) mol/L BQ-123 treatment, ET-1 decreased RPP and increased NO release in control kidneys. DOCA-salt rats responded to these agents with much less NO release. BQ-3020 at up to 10(-10) mol/L caused vasodilation (RPP, 10(-11) mol/L, -5.4 +/- 1.7%, P < .01) associated with increased NO release in control kidneys (+9.0 +/- 2.7 fmol.min-1.g-1 kidney wt, P < .01). However, in DOCA-salt kidneys, BQ-3020 caused renal vasoconstriction (RPP, +5.4 +/- 2.4%, P < .01 versus control) and a much smaller NO release (+1.1 +/- 0.4 fmol.min-1.g-1 kidney wt, P < .01 versus control). Northern blot analysis revealed that renal ETB mRNA was significantly decreased in DOCA-salt rat kidneys compared with controls (0.36 +/- 0.13 versus 1.00 +/- 0.23, P < .05).. These results suggest that ET-1 and ET-3 release EDNO via ETB receptors in renal vessels. ETB-mediated NO release was reduced in DOCA-salt rats, which may modulate renal function and thus blood pressure regulation in DOCA-salt hypertensive rats.

Topics: Animals; Desoxycorticosterone; Endothelin Receptor Antagonists; Endothelins; Hypertension; Kidney; Luminescent Measurements; Nitric Oxide; Peptide Fragments; Peptides, Cyclic; Rats; Rats, Wistar; Receptor, Endothelin B; Receptors, Endothelin; Sodium Chloride; Vascular Resistance

1. We examined the effects of a selective endothelin A (ETA)-receptor antagonist, BQ-123, on the development of hypertension and organ damage in stroke-prone spontaneously hypertensive rats (SHRSP) given 1% NaCl for 6 weeks. 2. BQ-123 at doses of 0.7, 2.1 and 7.1 mg/day was continuously administered for 6 weeks to 8 week old salt-loaded SHRSP, who were given water containing 1% NaCl for the following 6 weeks, via a subcutaneous osmotic minipump. 3. Development of high blood pressure was accelerated in salt-loaded SHRSP compared with that in non-salt-loaded SHRSP. After 6 weeks of salt-loading, incidence of cerebral infarction, renal sclerosis and renal fibrosis were greater in salt-loaded than non-salt-loaded SHRSP. 4. BQ-123 attenuated the age-related rise in blood pressure in a dose-dependent manner. The effect coincided with reduction in the incidence of cerebral infarction and prevention of renal sclerosis and fibrosis. Kidney function was improved as observed by an increase in glomerular filtration rate and decreases in urinary protein excretion, blood urea nitrogen and fractional sodium excretion. Furthermore, BQ-123 prevented increases in the heart weight/bodyweight ratio and aortic wall thickness in salt-loaded SHRSP. 5. These results suggest that endogenous endothelin-1 (ET-1) and ETA-receptors may be, at least in part, involved in the pathogenesis of hypertension and organ damage in salt-loaded SHRSP.

Topics: Animals; Blood Pressure; Blood Urea Nitrogen; Cerebrovascular Disorders; Dose-Response Relationship, Drug; Endothelin Receptor Antagonists; Glomerular Filtration Rate; Hypertension; Infarction; Kidney; Kidney Diseases; Kidney Function Tests; Osmolar Concentration; Peptides, Cyclic; Proteinuria; Rats; Rats, Inbred SHR; Sodium; Sodium, Dietary

We investigated the effect of the ETA-receptor antagonist BQ 123 (1.0, 5.0, and 10 mg/kg/h i.v.) on the endothelin-1 (ET-1) (10(-8) M)-induced vasoconstriction of arterioles in the cremaster muscle preparation of anesthetized SHRs. ET-1 10(-8) M led to a constriction of the arterial microvessels most marked in A4 arterioles (-92.9%) and least marked in A1 (-17.3%). The ET-1-induced constriction of venules was much less pronounced and showed no dependence on the vessel type. BQ 123 1.0 mg/kg/h was ineffective in antagonizing the vasoconstrictor effect of ET-1 in arterioles. With 5.0 mg/kg/h BQ 123, the ET-1-induced arterial vasoconstriction was inhibited by 68% in A4, by 44% in A3, by 39% in A2, and by 10% in A1 arterioles. BQ 123 10 mg/kg/h blocked the vasoconstrictor effect of ET-1 in all arteriole types by 79-93% and also reduced diastolic blood pressure in SHRs significantly at the end of the infusion period (-12.6 mm Hg). The ET-1-induced slight venous constriction was not affected by BQ 123.

Topics: Animals; Arterioles; Endothelin Receptor Antagonists; Endothelins; Hypertension; Male; Peptides, Cyclic; Rats; Rats, Inbred SHR; Vasoconstriction; Venules

The renal endothelin (ET) system has been implicated in the maintenance of hypertension in spontaneously hypertensive rats (SHRs). However, little is known about the expression and cellular distribution of the ET receptor subtypes in the kidney of SHRs. We therefore analyzed the expression of ET receptor subtypes in the kidneys of 16-week-old SHRs. Wistar-Kyoto (WKY) rats served as controls. Furthermore, we investigate the effects of the ETA receptor antagonist BQ 123 and the mixed (ETA/ETB) receptor antagonist bosentan on mean arterial blood pressure (MAP), renal blood flow (RBF), and glomerular filtration rate (GFR) in conscious, chronically instrumented rats. In SHRs we found overexpression of the ETA in the glomeruli and smooth muscle cells of intrarenal arteries compared to age-matched WKY rats. Furthermore, our study revealed a pronounced upregulation of the ETB in the glomeruli of SHRs. Blockade of ETA and ETB receptors in SHR with bosentan as well as with BQ 123 led to a significant decrease in MAP and a significant increase in RBF, indicating that the ETA receptor plays a major role in the maintenance of high blood pressure and the regulation of RBF in SHRs. The blockade of both ETA and ETB receptors by bosentan has no further effect on MAP reduction or increase in RBF in SHRs compared to ETA blockade by BQ 123. In contrast, combined blockade of ETA and ETB receptors by bosentan significantly decreased GFR in SHRs, whereas no effect on GFR was observed in WKY rats, suggesting that the glomerular ETB overexpression in SHRs is of pathophysiologic relevance.

Topics: Animals; Endothelin Receptor Antagonists; Glomerular Filtration Rate; Hemodynamics; Hypertension; Kidney; Male; Peptides, Cyclic; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Receptors, Endothelin

1. To investigate the contribution of ETA and ETB receptors, calcium responses to the ETB agonist, IRL-1620, to endothelin-1 (ET-1) and to the ETA antagonist, BQ-123, were examined in primary cultured unpassaged vascular smooth muscle cells (VSMC) from mesenteric vessels of 3, 9 and 17 week old spontaneously hypertensive rats (SHR), Wistar and Wistar-Kyoto (WKY) rats using Fura-2 methodology. 2. IRL-1620 (10(-7) mol/L) and ET-1 (10(-9) mol/L) increased [Ca2+]i in all strains and ages. Responses to ET-1 and IRL-1620 were blunted in 17 week SHR. BQ-123 significantly reduced ET-1-stimulated [Ca2+]i. In endothelium-denuded mesenteric vessels, ET-1 and IRL-1620 induced significant [Ca2+]i responses. 3. Binding of ET-1 was significantly lower in mesenteric artery membranes from 17 week SHR compared to controls. 4. Thus, ETA and ETB receptors are present in rat mesenteric VSMC. In adult SHR, a reduced density of ET receptors results in decreased responses to IRL-1620 and to ET-1.

Topics: Animals; Endothelin Receptor Antagonists; Endothelins; Endothelium, Vascular; Hypertension; In Vitro Techniques; Male; Mesenteric Arteries; Muscle, Smooth, Vascular; Peptide Fragments; Peptides, Cyclic; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Rats, Wistar; Receptors, Endothelin

Experiments were designed to compare the distribution and physiological roles of endothelin (ET) receptor subtypes, ETA and ETB, in the kidneys of normotensive Sprague-Dawley (SD) and spontaneously hypertensive (SH) rats. Using [125I] ET-1 and subtype-selective ligands sarafotoxin 6c (S6c, ETB-selective agonist) and BQ123 (ETA-selective antagonist), the distribution of ETA and ETB receptors in SD rat kidney cortex, outer medulla and papilla was calculated to be 50:50, 30:70 and 10:90, respectively. The ET receptor subtypes in outer medulla and papilla of age-matched SH rats were similar to those of SD. However, in the cortex of SH rats, the ratio of ETA to ETB was 25:75 compared to 50:50 in SD rats. In addition, the affinity of the ET receptors was also higher in SH rats (117 pM vs. 235 pM). In the conscious SD rats, bolus i.v. injections of ET-1 and S6c elicited similar dose-dependent decrease in renal blood flow (RBF), which were unaffected by the infusion of the selective ETA receptor antagonist, BQ123. The SH rats were more sensitive to the renal vasoconstrictor effect of S6c and ET-1. Also, the dose-response curve to S6c was shifted to the left when compared to ET-1; however, BQ123 infusion abolished this difference. In renal clearance studies, BQ123 infusions decreased RBF and glomerular filtration rate (GFR) only in SH rats, and the fractional excretion of sodium only in SD rats. The combined data indicate that the distribution and functional roles of ETA and ETB receptor subtypes are altered in the kidneys of SH rats.

Topics: Animals; Blood Pressure; Dose-Response Relationship, Drug; Endothelin Receptor Antagonists; Endothelins; Hypertension; Kidney; Male; Peptides, Cyclic; Rats; Rats, Inbred SHR; Rats, Sprague-Dawley; Receptors, Endothelin; Renal Circulation; Vasoconstrictor Agents; Viper Venoms

To investigate the role of endothelin-1 in the pathogenesis of hypertension directly by using the selective endothelin subtype A-receptor antagonist BQ-123.. The antihypertensive and hemodynamic effects of sustained BQ-123 administration were examined in conscious, unrestrained spontaneously hypertensive rats (SHR), normotensive Wistar-Kyoto (WKY) rats and renin hypertensive rats.. Sustained infusions of BQ-123 (0.16-164 nmol/kg per min, intravenously, for 6 h) produced dose-dependent reductions in mean arterial pressure in SHR, the maximal reduction being obtained with a dose of 16 nmol/kg per min. This reversible response was evident up to 14 h after the cessation of antagonist infusion. The antihypertensive response to a maximal dose of BQ-123 was associated with bradycardia, but only a minimal reduction in cardiac output (since the stroke volume was elevated) in the SHR. Therefore, the antihypertensive effect of BQ-123 resulted from a decrease in total peripheral resistance. In contrast, in WKY rats the infusion of the high dose (164 nmol/kg per min, intravenously for 6 h) produced a small but significant reduction in mean arterial pressure. BQ-123 did not alter the pressor response or tachycardia observed in pithed SHR following stimulation of the thoracolumbar sympathetic outflow. BQ-123 was also antihypertensive in renin hypertensive rats, lowering the blood pressure to an extent similar to that observed in SHR.. The data presented indicate a role for endothelin in the pathophysiology of hypertension.

Topics: Animals; Antihypertensive Agents; Blood Pressure; Decerebrate State; Dose-Response Relationship, Drug; Electric Stimulation; Endothelin Receptor Antagonists; Hemodynamics; Hypertension; Male; Peptides, Cyclic; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Renin; Sympathetic Nervous System; Synaptic Transmission

To determine the differential calcium responses to two vasoconstrictor peptides, angiotensin II (Ang II) and endothelin-1, in vascular smooth muscle cells derived from mesenteric arteries from young and adult normotensive and hypertensive rats.. Effects of Ang II and endothelin-1 on cytosolic free calcium concentration in primary cultured unpassaged single vascular smooth muscle cells from mesenteric arteries of Wistar-Kyoto (WKY), Wistar and spontaneously hypertensive rats (SHR) aged 3, 9 and 17 weeks were examined microphotometrically using fura-2 methodology.. Basal cytosolic free calcium concentration was significantly increased in cells from SHR aged 9 and 17 weeks compared with cells from age-matched WKY and Wistar rats. Ang II and endothelin-1 significantly increased cell cytosolic free calcium in all rat groups at all ages. Responses to low concentrations of Ang II (1 nmol/l) were significantly higher in cells from SHR aged 9 and 17 weeks than in age-matched controls. This was confirmed in cells from rats aged 17 weeks with full concentration-response curves, which also showed that the pD2 for Ang II for WKY rats was significantly different from that of SHR. In cells from SHR at all ages Ang II-stimulated cytosolic free calcium remained persistently high, whereas in cells from WKY and Wistar rats basal levels were reached within 100 s after the maximal response. Low concentrations of endothelin-1 elicited significantly lower cytosolic free calcium responses in cells from SHR aged 17 weeks compared with age-matched controls. The time course of cytosolic free calcium responses to endothelin-1 were similar in the groups.. In primary cultured unpassaged mesenteric vascular smooth muscle cells from adult SHR, cytosolic free calcium concentration responses to Ang II are enhanced, whereas responses to low concentrations of endothelin-1 are slightly reduced. The differential effects of these two vasoconstrictor peptides may contribute to their relative roles in modulating vascular smooth muscle cell cytosolic free calcium in SHR.

Topics: 1-Sarcosine-8-Isoleucine Angiotensin II; Angiotensin II; Animals; Calcium; Cells, Cultured; Cytosol; Endothelins; Hypertension; Male; Mesenteric Arteries; Muscle, Smooth, Vascular; Peptides, Cyclic; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Rats, Wistar

An experimental model of hypertensive rat was made by abdominal aorta stenosis and hypersaline uptake. The blood pressure was significantly decreased by intracerebroventricular injection (i.c.v.) of BQ123 a potent antagonist of ET-1 receptor, in a dose-dependent manner. Negative chronotropic effect on the heart was produced by high dose of BQ123, while the depressor effect was produced by i.c.v. ET-antiserum. These results indicate that endothelin in CNS may play an important role in the pathological physiology of hypertension.

Topics: Animals; Aorta, Abdominal; Blood Pressure; Constriction; Endothelins; Hypertension; Immune Sera; Injections, Intraventricular; Male; Peptides, Cyclic; Rats; Rats, Wistar; Sodium Chloride

We determined the antihypertensive effects of BQ-123 (cyclo(D-Trp-D-Asp-L-Pro-D-Val-L-Leu-), sodium salt), a selective endothelin ETA receptor antagonist, in spontaneously hypertensive rats treated with deoxycorticosterone acetate-salt (DOCA-salt SHR). BQ-123 (1-30 mg/kg/h) decreased blood pressure in DOCA-salt SHR in a dose-dependent manner, although plasma immunoreactive endothelin-1 did not significantly increase and the maximal contractile response to endothelin-1 in the aorta significantly decreased as compared with values observed in age-matched SHR. These results suggest that endogenous endothelin-1 is involved in the maintenance of hypertension in DOCA-salt SHR, and that circulating endothelin-1 is not sufficient to reflect the physiological role of endothelin-1.

Topics: Amino Acid Sequence; Animals; Antihypertensive Agents; Aorta, Thoracic; Blood Pressure; Desoxycorticosterone; Dose-Response Relationship, Drug; Endothelin Receptor Antagonists; Endothelins; Hypertension; In Vitro Techniques; Male; Molecular Sequence Data; Muscle, Smooth, Vascular; Peptides, Cyclic; Rats; Rats, Inbred SHR

The role of different endothelin (ET) receptors in the hemodynamic action of ET-1 was investigated with an ETA-receptor antagonist, BQ-123, in anesthetized Wistar rat. BQ-123 (10 mg/kg/0.1 ml) was injected 5 min before ET-1 injection (1 nmol/kg). IV injection of ET-1 induced a short period of hypotension associated with aortic vasodilation, followed by long-lasting hypertension and aortic vasoconstriction. These effects were concomitant with immediate renal and mesenteric vasoconstriction. In the presence of BQ-123, the hypotension and aortic vasodilation induced by ET-1 were prolonged and the subsequent hypertension and aortic constriction were prevented. In the renal vascular bed, BQ-123 did not significantly affect the initial ET-1-induced constriction but markedly shortened its duration. In contrast, in the mesenteric vascular bed, BQ-123 seemed initially to amplify the ET-1-induced constriction, but afterwards slightly reduced it. The hemodynamic response to ET-1 may be mediated at first by ETB receptors, which induce a reduction of systemic blood pressure and regional vasoconstriction. In a second phase, ETA receptors operate to induce a systemic pressor effect and participate with ETB receptors in regional vasoconstriction. Therefore, ETA and ETB receptors may exist in various proportions in different vessels, the renal vascular bed appearing to be richer in ETA receptors than the mesenteric bed. The results, which demonstrate that ETB receptors mediate aortic dilation and regional constriction, are unexpected and suggest the existence of another non-ETA-type receptor and/or a different localization of non-ETA receptors in the vascular wall.

Topics: Animals; Endothelin Receptor Antagonists; Endothelins; Hemodynamics; Hypertension; Male; Peptides, Cyclic; Rats; Rats, Wistar; Receptors, Endothelin; Vasoconstriction; Vasodilation

We reported previously that the endothelin converting enzyme (ECE) inhibitor phosphoramidon lowers mean arterial pressure (MAP) when infused in conscious, spontaneously hypertensive rats (SHRs). In this study we determined the dose-response relationship for this action in SHRs and in a high-renin hypertensive model, the renal artery-ligated rat. We also determined whether the ETA receptor antagonist BQ-123 (cyclo [D-Trp-D-Asp-Pro-D-Val-Leu]) might lower MAP in hypertensive rats. Phosphoramidon lowered MAP by 9 +/- 4, 31 +/- 4, and 40 +/- 4 mm Hg after 5 h when infused in SHRs at 10, 20, and 40 mg/kg/h. This lowering of MAP was associated with dose-related inhibition of the pressor response to a bolus intravenous injection of big ET (1-39) at 1 nmol/kg. BQ-123 also lowered MAP in SHRs (by 25 +/- 3 mm Hg), but only at a very high dose (50 mg/kg/h for 5 h). At this dose, BQ-123 blocked the pressor response to a bolus intravenous injection of ET-1 (1 nmol/kg), but the blockade was incomplete. Phosphoramidon infused in conscious, renal hypertensive rats lowered MAP by 31 +/- 9, 46 +/- 8, and 54 +/- 1 mm Hg after 5 h at 10, 20, and 40 mg/kg/h, respectively. This lowering of MAP was associated with blockade of the pressor response to big ET (1-39). BQ-123 did not lower MAP in renal hypertensive rats when infused at 30 mg/kg/h for 5 h.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Amino Acid Sequence; Angiotensin I; Animals; Aspartic Acid Endopeptidases; Blood Pressure; Dose-Response Relationship, Drug; Endothelin Receptor Antagonists; Endothelin-1; Endothelin-Converting Enzymes; Endothelins; Glycopeptides; Hypertension; Hypertension, Renal; Male; Metalloendopeptidases; Molecular Sequence Data; Neprilysin; Peptides, Cyclic; Protein Precursors; Rats; Rats, Inbred SHR; Rats, Sprague-Dawley

The aims of this study were to determine the relations between platelet free calcium concentrations ([Ca2+]i), intracellular pH (pHi), and aggregation and to assess the effects of angiotensin II (Ang II) and endothelin-1 on these platelet parameters in normotensive subjects and hypertensive patients. Seventeen normotensive subjects, 25 untreated hypertensive patients, and 34 treated hypertensive patients were studied. Platelet cytosolic free [Ca2+]i and pHi were measured spectrofluorometrically using specific fluorescent probes (fura 2-AM and BCECF-AM, respectively) in unstimulated and Ang II- and endothelin-1-stimulated platelets. Aggregation was measured by a turbidometric technique. Basal [Ca2+]i (141 +/- 11 nmol/L) and pH (7.16 +/- 0.01) were higher (P < .05) in the untreated hypertensive group compared with the normotensive (118 +/- 9 nmol/L, 7.11 +/- 0.01, respectively) and treated hypertensive (121 +/- 11 nmol/L, 7.12 +/- 0.01, respectively) groups. In the combined normotensive and hypertensive groups, there were significant correlations between [Ca2+]i and mean arterial pressure (r = .75, P < .01), pHi and mean arterial pressure (r = .72, P < .01), [Ca2+]i and pHi (r = .71, P < .01), [Ca2+]i and aggregation (r = .69, P < .02), and pHi and aggregation (r = .56, P < .05). Ang II stimulation significantly increased [Ca2+]i and pHi in the untreated hypertensive and normotensive groups. The net change in [Ca2+]i induced by Ang II was significantly higher (P < .05) in the untreated hypertensive group compared with the other groups (67 +/- 6 nmol/L for the untreated hypertensive group versus 54 +/- 5 and 29 +/- 8 nmol/L for the normotensive and treated hypertensive groups, respectively). In the presence of Ang II, thrombin-induced aggregatory responses were increased in all three groups, but the maximal response was significantly higher in the untreated hypertensive group compared with the other groups (P < .05). Endothelin-1 increased pHi through endothelin A-receptors (effect blocked by the specific antagonist BQ-123) but had no significant effect on [Ca2+]i or aggregation. However, endothelin-1 blunted thrombin-induced platelet aggregation in normotensive subjects but not in hypertensive patients. In conclusion, increased Ang II-stimulated [Ca2+]i and pHi in platelets of essential hypertensive patients may be associated with increased aggregatory responses. The stimulatory effect of endothelin-1 on pHi but not on [Ca2+]i or aggregation suggests that i

Topics: Adult; Aged; Amiloride; Analysis of Variance; Angiotensin II; Blood Platelets; Calcium; Cytosol; Dose-Response Relationship, Drug; Endothelin Receptor Antagonists; Endothelins; Female; Humans; Hydrogen-Ion Concentration; Hypertension; In Vitro Techniques; Male; Middle Aged; Peptides, Cyclic; Platelet Aggregation; Receptor, Endothelin A; Receptors, Endothelin; Regression Analysis; Saralasin

A newly synthesized ET(A)-selective antagonist, BQ-123, was examined with respect to its anti-endothelin(ET) action in vitro and in vivo and its effect on blood pressure in Wistar Kyoto rats (WKY), spontaneously hypertensive rats (SHR) and stroke-prone spontaneously hypertensive rats (SHRSP). In isolated porcine coronary arteries, BQ-123 (0.07 microM to 6.0 microM) shifted the concentration-response curve for ET-1 to the right without affecting the maximal response of ET-1, its pA2 value being 7.35. Intravenous infusion of BQ-123 at a rate of 1.2 and 30 mg/kg/hr produced a significant decrease in blood pressure in 20- to 29-week-old SHRSP, but did not alter blood pressure in 13- to 16-week-old WKY or in 18- to 19-week-old and 40-week-old SHR. The hypotensive effect of BQ-123 depended on the pretreatment blood pressure level. These results suggest that ET-1 is involved in part in the maintenance of high blood pressure in malignant hypertension, as exemplified by SHRSP.

Topics: Amino Acid Sequence; Analysis of Variance; Animals; Antihypertensive Agents; Endothelins; Endothelium, Vascular; Hypertension; In Vitro Techniques; Male; Models, Genetic; Molecular Sequence Data; Peptides, Cyclic; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Swine

The present experiments describe the endothelin-1 (ET-1) antagonist activity of BQ123 (cyclic D-Asp-L-Pro-D-Val-L-Leu-D-Trp) in conscious Sprague-Dawley (SD) rats, and we also examined the effect blockade of ETA receptors had on blood pressure in four experimental models of hypertension. Rats were anesthetized with methoxyflurane and instrumented with femoral arterial and venous catheters. In SD rats, BQ123 (0.1-10.0 mg/kg i.v.) administered 5 or 60 min prior to ET-1 inhibited both the magnitude and duration of the ET-1 (0.25 nmol/kg i.v.) pressor response. In addition, BQ123 (10.0 mg/kg) inhibited the pressor response evoked by administration of the ET-1 precursor, proendothelin-1 (1.0 nmol/kg). However, BQ123 (10.0 mg/kg) had no effect on the pressor response evoked by ET-3 (0.75 nmol/kg). In Wistar-Kyoto rats, BQ123 (10.0 mg/kg) reversed the hypertension produced by an infusion of ET-1 (0.01 nmol/kg/min). Administration of BQ123 produced a mild antihypertensive effect in normal- to low-renin models of hypertension, but no blood pressure lowering was observed in high-renin models of hypertension. These studies demonstrated the selectivity of the ETA receptor antagonist, BQ123 for ET-1, but not ET-3-induced pressor responses. Furthermore, ET-1 does not appear to be a major contributing factor to the maintenance of elevated levels of blood pressure in four experimental models of hypertension.

Topics: Amino Acid Sequence; Animals; Aorta, Thoracic; Blood Pressure; Desoxycorticosterone; Dose-Response Relationship, Drug; Endothelin Receptor Antagonists; Endothelins; Hypertension; Male; Molecular Sequence Data; Peptides, Cyclic; Rats; Rats, Inbred WKY; Rats, Sprague-Dawley

Topics: Animals; Atrial Natriuretic Factor; Blood Pressure; Cells, Cultured; Endothelins; Glomerular Mesangium; Humans; Hypertension; Muscle, Smooth, Vascular; Natriuretic Peptide, Brain; Nerve Tissue Proteins; Peptides, Cyclic; Rats