irl-1620 and Hypertension

Endothelins regulate catecholaminergic activity in the olfactory bulb (OB) in normotensive and hypertensive animals. Administration of an endothelin ET

Topics: Animals; Blood Pressure; Desoxycorticosterone; Endothelins; Heart Rate; Hypertension; Male; Nitric Oxide Synthase Type I; Olfactory Bulb; Peptide Fragments; Rats; Rats, Sprague-Dawley; Receptor, Endothelin B; RNA, Messenger; Sympathetic Nervous System

In the vascular system, endothelin (ET) type B (ET(B)) receptors for ET-1 are located on endothelial and on venous and arterial smooth muscle cells. In the present study, we investigated the hemodynamic effects of chronic ET(B) receptor blockade at low and high doses in the Syrian Golden hamster. After 16 days of gavage with A-192621 (0.5 or 30 mg.kg(-1).day(-1)), a selective ET(B) receptor antagonist, hamsters were anesthetized with a mixture of ketamine and xylazine (87 and 13 mg/kg im, respectively), and basal mean arterial blood pressure (MAP) and pressor responses to exogenous ET-1 were evaluated. The lower dose of A-192621 (0.5 mg.kg(-1).day(-1)) did not modify basal MAP, whereas the higher dose (30 mg.kg(-1).day(-1)) increased MAP and plasma ET levels. Radio-telemetry recordings confirmed the increase in MAP induced by the higher dose of A-192621 in conscious hamsters. On the other hand, although the lower dose of A-192621 was devoid of intrinsic pressor effects, it markedly reduced the transient hypotensive phase induced by intravenously injected IRL-1620, a selective ET(B) receptor agonist. Finally, A-192621 (0.5 mg.kg(-1).day(-1)) alone or A-192621 (30 mg.kg(-1).day(-1)) + atrasentan (6 mg.kg(-1).day(-1)), a selective ET(A) receptor antagonist, potentiated the pressor response to exogenous ET-1. Our results suggest that, in the hamster, ET(B) receptors on vascular smooth muscle cells are importantly involved in the clearance of endogenous ET-1, whereas the same receptor type on the endothelium is solely involved in the vasodilatory responses to the pressor peptide. Blockade of endothelial and vascular smooth muscle cell ET(B) receptors triggers a marked potentiation of ET(A)-dependent increases in systemic resistance.

Topics: Anesthesia; Animals; Atrasentan; Blood Pressure; Consciousness; Cricetinae; Dose-Response Relationship, Drug; Endothelin B Receptor Antagonists; Endothelin-1; Endothelins; Endothelium, Vascular; Hypertension; Male; Mesocricetus; Muscle, Smooth, Vascular; Peptide Fragments; Pyrrolidines; Receptor, Endothelin A; Receptor, Endothelin B

We previously demonstrated a differential activation of the endothelin-1 (ET-1) pathway in male and female deoxycorticosterone (DOCA)-salt hypertensive rats, with the male rats exhibiting marked alterations in vascular and pressor responses to ET-1 and Suc-[Glu,(9)Ala(11,15)]-ET-1(8-21) (IRL-1620), an ET(B) agonist. Mechanisms underlying these gender differences are unclear, and we hypothesized that the ovarian hormones attenuate vascular ET(B) responses in female DOCA-salt rats. Female Wistar rats were randomized in 3 groups: sham-operated, ovariectomized (OVX), and OVX plus hormone replacement with estradiol (E) or estradiol/progesterone (EP). Two weeks later, rats were uninephrectomized and further randomized in DOCA-salt (subcutaneous injections of desoxycorticosterone and drinking water containing NaCl/KCl) and control normotensive (subcutaneous injections of vehicle and tap water). Blood pressure was evaluated both by direct and standard tail-cuff methods. Responses to IRL-1620 were evaluated in vivo/in situ in the mesenteric microcirculation. mRNA expression of ET-1 and ET(A/B) receptors was evaluated in mesenteric arteries by reverse transcription-polymerase chain reaction and expressed relative to GAPDH. OVX-DOCA rats developed a more severe form of hypertension than did DOCA rats. Treatment with E or EP restored blood pressure to levels observed in DOCA rats. In the mesentery, IRL-1620 induced vasodilatation in control rats, a mild vasoconstriction in DOCA rats, and marked vasoconstriction in OVX-DOCA rats. Both E and EP decreased IRL-1620-induced vasoconstriction in the DOCA group. In the normotensive group, OVX did not change blood pressure or IRL-1620-induced vasodilation. Removal of the ovaries increased ET-1 mRNA in arteries from DOCA and control rats, although treatment with E or EP reversed these changes. Vascular ET(B) receptor mRNA levels were greatly enhanced in OVX-DOCA but not OVX-control rats. Hormone replacement with E or EP restored ET(B) receptor expression in the DOCA group. A greater blood pressure-lowering effect of bosentan (ET(A)/ET(B) blocker) was observed in OVX-DOCA rats. The observation that OVX worsens hypertension as well as the altered ET(B) receptor-mediated responses and the effects of bosentan in female DOCA rats supports our suggestion that the ovarian hormones modulate ET-1/ET(B) receptor vascular responses/expression in DOCA-salt hypertension.

Topics: Animals; Blood Pressure; Body Weight; Desoxycorticosterone; Endothelin-1; Endothelins; Estradiol; Female; Hypertension; In Vitro Techniques; Mesenteric Arteries; Organ Size; Ovariectomy; Peptide Fragments; Potassium, Dietary; Progesterone; Rats; Rats, Wistar; Receptor, Endothelin A; Receptor, Endothelin B; Receptors, Endothelin; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Sodium Chloride, Dietary; Time Factors; Uterus; Vasoconstriction

1. Male DOCA-salt rats exhibit vasoconstriction upon ET(B) activation. Because hypertension is less severe in female than male DOCA rats, we hypothesized that female DOCA rats would display attenuated ET(B) vasoconstrictor responses. 2. Uninephrectomized Wistar rats received DOCA and drinking water containing NaCl/KCl. Control rats received vehicle and tap water. Systolic blood pressure was higher in male vs female DOCA rats. Responses to endothelin-1 (ET-1), IRL-1620, an ET(B) agonist, and acetylcholine were evaluated in isolated aortas and in vivo in the mesenteric microcirculation. 3. Endothelium-denuded aortas from male, but not female, DOCA rats displayed increased sensitivity to ET-1. IRL-1620 contracted aortas from male DOCA rats, but not control or female DOCA aortas. Noradrenaline-constricted and endothelium-intact aortas from male, but not female, DOCA rats displayed increased relaxation to IRL-1620 compared to control aortas. 4. In vivo, increased vasoconstriction to ET-1 was observed in male and female DOCA rats. IRL-1620 induced vasodilation in control rats, but vasoconstriction in male DOCA rats. There were minimal changes in diameter in vessels from female DOCA rats. 5. The initial fall in blood pressure induced by ET-1 and IRL-1620 was attenuated in male DOCA rats. Bosentan, a mixed ET(A)/ET(B) receptor antagonist, lowered blood pressure in male and female DOCA rats, but a greater and marked decrease occurred in the male DOCA group. 6. The gender-related differences in ET-1/ET(B)-mediated effects both in the vasculature and blood pressure suggest that sex-related functional up-regulation of ET(B) receptors may play a role in the more severe hypertension in male DOCA hypertensive rats.

Topics: Animals; Aorta; Blood Pressure; Desoxycorticosterone; Endothelin-1; Endothelins; Female; Hypertension; In Vitro Techniques; Male; Peptide Fragments; Rats; Rats, Wistar; Receptor, Endothelin B; Receptors, Endothelin; Sex Characteristics; Sodium Chloride; Vasoconstriction

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

In experimental models of hypertension, blood pressure reaches a higher level in male than in female rats. Because endothelin-1 (ET-1) seems to play a role in blood pressure elevation in deoxycorticosterone acetate (DOCA)-salt hypertension, we hypothesized that male DOCA-salt rats would display a greater vascular responsiveness to ET-1 than female DOCA-salt rats. Male and female Wistar rats were uninephrectomized, received DOCA injections (50 mg/kg/week) and water plus 1.0% NaCl/0.2% KCl. Control rats received vehicle and tap water. Responses to ET-1, norepinephrine (NE), serotonin (5-HT), IRL-1620, a selective endothelin-B- (ET(B)) receptor agonist, and acetylcholine (ACh) were evaluated in isolated aortic rings and also in vivo in the mesenteric microcirculation. Endothelium-intact aortas from male and female DOCA rats displayed increased sensitivity (p < 0.05) to NE and 5-HT, but decreased relaxation to ACh in comparison to aortas from respective control male and female rats. Endothelium-denuded, but not endothelium-intact, arteries from male DOCA rats displayed increased sensitivity (-log EC20) to ET-1, but no changes in ET-1 sensitivity were observed in female DOCA aortas. IRL-1620 induced contraction in male DOCA aortas, but not in female DOCA or control endothelium-denuded aortas. In the microcirculation, IRL-1620 induced vasodilation in male and female control rats, but marked vasoconstriction in male DOCA and minimal changes in vessels diameter in female DOCA rats. Bosentan, an ET(A)/ET(B)-receptor antagonist, induced a greater decrease in mean arterial blood pressure in male than in female DOCA-salt hypertensive rats. These data support the hypothesis that DOCA-salt rats exhibit gender differences in ET-1 vascular reactivity, which probably result from functional changes in ET(B)-receptors. The increased ET(B) responses in male DOCA-salt hypertensive rats may play a role in their higher blood pressure levels.

Topics: Animals; Desoxycorticosterone; Endothelin-1; Endothelins; Female; Hypertension; In Vitro Techniques; Male; Peptide Fragments; Rats; Rats, Wistar; Sex Characteristics; Sodium Chloride; Vasoconstriction

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

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 evaluate the functional responses of mesenteric small resistance arteries of spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rat controls to endothelin-1 (ET-1), in the presence and absence of an ET(A) receptor antagonist drug as well as to an ET(B) receptor agonist.. Twenty rats aged 12 weeks were studied. They were 10 SHR and 10 WKY rats. Mesenteric small resistance arteries (relaxed diameter 100-180 microm) were dissected and mounted on a micromyograph (Mulvany's technique). A dose-response curve for response to ET-1 was plotted for cumulative concentrations (from 10(-11) to 10(-8) mol/l) in the presence and absence of 10(-6) mol/l FR 139317 (a selective antagonist of ET(A) receptors). In addition, the effects of 10(-7) mol/l N-succinyl-[Glu9, Ala11,15]-endothelin 1 fragment 8-21 (IRL 1620, a selective agonist of ET(B) receptors) were evaluated.. The response of ET-1 was greater in WKY rats than it was in SHR. Almost all the vasoconstrictor effect of ET-1 could be prevented by addition of FR 139317, whereas the agonist of ET(B) receptors had no effect (no change in active force).. The contractile effects of ET-1 on mesenteric small resistance arteries of SHR and WKY rats are mediated mostly by ET(A) receptors, whereas ET(B) receptors play a minor role, if any. It is possible, however, that a vasoconstrictor effect of ET(B) receptors on the smooth muscle could be masked by the concomitant stimulation of endothelial ET(B) vasodilator receptors.

Topics: Animals; Azepines; Dose-Response Relationship, Drug; Endothelin-1; Endothelins; Hypertension; Indoles; Mesenteric Arteries; Muscle, Smooth, Vascular; Peptide Fragments; Rats; Rats, Inbred SHR; Rats, Wistar; Receptor, Endothelin A; Receptor, Endothelin B; Receptors, Endothelin; Vascular Resistance; Vasoconstriction

We tested the hypothesis that responses of the basilar artery to selective activation of endothelin-B receptors are altered during chronic hypertension. Using a cranial window in anesthetized rats, we examined responses of the basilar artery to a selective endothelin-B receptor agonist, IRL 1620, in stroke-prone spontaneously hypertensive rats (SHRSP). Under control conditions, baseline basilar artery diameter was smaller in SHRSP (196 +/- 8 microns [mean +/- SEM]) than in normotensive Wistar-Kyoto rats (WKY) (245 +/- 9 microns, P < .05). Topical application of IRL 1620 (10(-8) mol/L) dilated the basilar artery by 27 +/- 5% in WKY and 56 +/- 4% in SHRSP (P < .05). Dilatation of the basilar artery in response to sodium nitroprusside was similar in WKY and SHRSP. In contrast, acetylcholine-induced vasodilatation in SHRSP was markedly impaired. NG-Nitro-L-arginine methyl ester and NG-nitro-L-arginine, inhibitors of nitric oxide synthase, inhibited IRL 1620-induced vasodilatation in WKY. Neither NG-nitro-L-arginine methyl ester nor indomethacin attenuated vasodilatation produced by IRL 1620 in SHRSP. The major finding is that dilator responses of the basilar artery to selective activation of endothelin-B receptors are paradoxically enhanced in SHRSP compared with WKY. Dilator responses of the basilar artery to endothelin-B receptor activation are mediated by endothelium-derived relaxing factor in WKY. In contrast, responses to activation of endothelin receptors in SHRSP do not depend on the production of nitric oxide or prostanoids.

Topics: Acetylcholine; Animals; Arginine; Basilar Artery; Drug Interactions; Endothelins; Hypertension; Indomethacin; Male; Muscle, Smooth, Vascular; NG-Nitroarginine Methyl Ester; Nitric Oxide; Peptide Fragments; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Receptor, Endothelin B; Receptors, Endothelin; Species Specificity; Vasodilation

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