Vascular effects of estrogens: rapid actions, novel mechanisms, and potential therapeutic implications

Although estrogen-dependent effects on the vasculature were first observed more than a century ago, many of the mechanisms by which estrogens interact with the vascular wall have been identified only in the past 15 years. Estrogens bind to vascular estrogen receptors (ER), including the ER alpha, the novel ER beta as well as to membrane-bound receptors. Estrogens have direct effects in human coronary and internal mammary arteries by inducing rapid, endothelium-independent relaxation, enhancement of endothelial function and inhibition of vasoconstriction by vasoactive agonists. Furthermore, estrogens contribute to vascular homeostasis through modulation of gene expression, changes in membrane potentials, as well as expression and function of receptors. In addition, estrogens interfere with the activity of vasoactive peptides and vascular enzymes and act as natural antioxidants. Some of these effects have also been observed for phyto-estrogens, which are important dietary components in Asian countries. In the vasculature, the sum of these actions of estrogens results in vasodilatation and inhibition of vascular cell growth. Accordingly, estrogens have been shown to improve vascular function of animals and humans and to inhibit the response to injury after balloon angioplasty and the progression of atherosclerosis. Prospective clinical studies are ongoing to determine whether replacement therapy with estrogen or derivatives provides an alternative to lower cardiovascular mortality in postmenopausal women.

Endothelial dysfunction in the aorta of transgenic rats harboring the mouse Ren-2 gene

The renin-angiotensin system plays an important role in the pathophysiology of hypertension. We studied vascular function in the aorta of mouse Ren-2 transgenic rats (TGR(mRen2)27). Changes in isometric tension of isolated aorta of TGR(mRen2)27 and Sprague-Dawley rats (SD) were recorded in organ chambers. Contractions to angiotensin II (AII), big-endothelin and endothelin-1 (ET-1), but not KCl were decreased in TGR. Blockade of nitric oxide (NO)-synthase by L-NAME or removal of the endothelium did not alter these decreased contractions to ET-1 and AII in TGR, suggesting that receptors or signaling pathways of these two agonists are downregulated during hypertension. Contractions to norepinephrine (NE) were also lower in TGR, however blockade of NO-synthase by L-NAME or removal of the endothelium evoked similar contractions to NE in both strains, suggesting that basal release of NO reduces contractions to NE to a greater extent in transgenic than control rats. In the presence of L-NAME, acetylcholine evoked endothelium-dependent contractions (EDCF) in TGR, which were blocked by the thromboxane/prostaglandin H2 receptor antagonists SQ 30741, and partially by the thromboxane synthase inhibitor CGS 13080, suggesting that prostaglandin H2 is the mediator. Endothelium-dependent relaxation to acetylcholine was decreased in TGR, while endothelium-independent relaxations to sodium nitroprusside were similar in both strains. SQ 30741 did not improve relaxations to acetylcholine in TGR indicating that impaired relaxations to acetylcholine are due to a decreased acetylcholine-receptor mediated release of NO rather than increased release of EDCF. Thus, Ren-2 hypertension leads to marked alterations of vascular functions in the aorta. These changes could contribute to hypertension and its vascular complications in TGR(mRen2)27 rats.

Endothelial dysfunction in acute renal failure: role of circulating and tissue endothelin-1

The kidney is an important target and source of the potent vasoconstrictor and mitogen endothelin-1 (ET-1). However, its exact role in acute renal failure (ARF) remains to be determined. ARF was induced in male Wistar-Kyoto rats (n = 7) in a 2-kidney, 2-clip model of 30-min clamping. Twenty-four hours after clamp release, contractions to angiotensin I (Angl) and II, ET-1, and big ET-1 were studied in isolated aortic and renal artery rings. Endothelium-dependent and -independent relaxations were assessed by acetylcholine and sodium nitroprusside. ET-1 clearance, tissue uptake, plasma levels, and vascular and kidney content were investigated. In addition, ET(A) and Et(B) receptor mRNA expression was determined. Sham-operated animals served as controls (n = 7). In ARF, ET-1 plasma levels and tissue content of the renal artery, the aorta, and the kidney markedly increased (P<0.01). Plasma half-life of radiolabeled 125I-ET-1 was markedly prolonged, whereas 125I-ET-1 tissue uptake decreased in the kidney in ARF. Contractions to AngI and AngII were blunted (P<0.05) and those to KCl were unchanged, whereas vascular responses to big ET-1 and ET-1 were enhanced in the renal artery and also in the aorta in ARF (P<0.05 to 0.001). Correspondingly, ET(A) and Et(B) receptor mRNA expression significantly increased in both vascular beds. In addition, endothelium-dependent relaxation to acetylcholine was diminished and inversely correlated with vascular ET-1 protein levels in the renal artery (r = -0.827, P<0.001) and the aorta (r = -0.812, P<0.001). In conclusion, the present study demonstrates that increase of circulating and tissue ET-1 protein levels and ET(A) and Et(B) receptor gene expression occurs, which induces endothelial dysfunction and enhanced vasoconstriction in different vascular beds in ARF.

Endothelin in heart failure

Congestive heart failure is a complex disease that results from pumping failure of the cardiac muscle and adaptational processes of the cardiovascular system to correct for the reduced blood supply to the organism. It is associated with increased vasoconstriction and impaired vasodilation in response to physical activity. The elevated vasoconstrictor tone is caused by the activation of compensatory mechanisms including the sympathetic nervous system and stimulation of the release of neurohormones like angiotensin II, catecholamines, and vasopressin. Furthermore, the vascular endothelium is importantly involved in the regulation of vascular tone as it releases a variety of vasoactive substances that act locally and systemically. In congestive heart failure, there is a marked imbalance between the diminished release or the increased inactivation of vasodilators on the one hand, ie, nitric oxide, and the elevated production, release, or reduced inactivation of vasoconstrictors such as endothelin-1 on the other hand. In addition to its very potent vasoconstrictor effects, endothelin-1 possesses antinatriuretic and mitogenic properties that are a common feature of substances that are involved in development of the deleterious consequences that render congestive heart failure a lethal disease. The spectrum of action of the endothelin system and the advent of specific antagonists for its receptors have made this system a very interesting target for clinical research and possibly for future therapeutic approaches.

17Beta-estradiol acutely improves endothelium-dependent relaxation to bradykinin in isolated human coronary arteries

Improvement of endothelial function has been implicated in the cardioprotective effects of estrogens in women. In isolated human coronary arteries, we investigated whether 17beta-estradiol affects endothelium-dependent responses to bradykinin, an endothelium-derived vasodilator locally produced by endothelial cells. Concentration-response curves to bradykinin (0.03-300 nM) or nitroglycerine (0.01-1 microM) were obtained before and after 30 min of incubation with 17beta-estradiol (3 microM) or solvent control (ethanol 0.2% vol/vol). Incubation with 17beta-estradiol enhanced relaxations to bradykinin (from 43 +/- 6 to 83 +/- 3%, P < 0.0001) but not those to nitroglycerine (n.s.). Improvement of bradykinin-mediated endothelium-dependent relaxation may represent a novel mechanism contributing to the cardioprotective effects of estrogen in women.

Endothelin ETA receptor blockade restores NO-mediated endothelial function and inhibits atherosclerosis in apolipoprotein E-deficient mice

This study investigated whether endothelin-1 (ET-1), a potent vasoconstrictor, which also stimulates cell proliferation, contributes to endothelial dysfunction and atherosclerosis. Apolipoprotein E (apoE)-deficient mice and C57BL/6 control mice were treated with a Western-type diet to accelerate atherosclerosis with or without ETA receptor antagonist LU135252 (50 mg/kg/d) for 30 wk. Systolic blood pressure, plasma lipid profile, and plasma nitrate levels were determined. In the aorta, NO-mediated endothelium-dependent relaxation, atheroma formation, ET receptor-binding capacity, and vascular ET-1 protein content were assessed. In apoE-deficient but not C57BL/6 mice, severe atherosclerosis developed within 30 wk. Aortic ET-1 protein content (P < 0.0001) and binding capacity for ETA receptors was increased as compared with C57BL/6 mice. In contrast, NO-mediated, endothelium-dependent relaxation to acetylcholine (56 +/- 3 vs. 99 +/- 2%, P < 0.0001) and plasma nitrate were reduced (57.9 +/- 4 vs. 93 +/- 10 micromol/liter, P < 0.01). Treatment with the ETA receptor antagonist LU135252 for 30 wk had no effect on the lipid profile or systolic blood pressure in apoE-deficient mice, but increased NO-mediated endothelium-dependent relaxation (from 56 +/- 3 to 93 +/- 2%, P < 0.0001 vs. untreated) as well as circulating nitrate levels (from 57.9 +/- 4 to 80 +/- 8.3 micromol/liter, P < 0.05). Chronic ETA receptor blockade reduced elevated tissue ET-1 levels comparable with those found in C57BL/6 mice and inhibited atherosclerosis in the aorta by 31% without affecting plaque morphology or ET receptor-binding capacity. Thus, chronic ETA receptor blockade normalizes NO-mediated endothelial dysfunction and reduces atheroma formation independent of plasma cholesterol and blood pressure in a mouse model of human atherosclerosis. ETA receptor blockade may have therapeutic potential in patients with atherosclerosis.

Endothelial vasoconstrictor prostanoids, vascular reactivity, and acute renal failure

The interaction of endothelium-derived vasoconstrictor prostaglandins, the angiotensins (Ang), and the sympathetic nervous system in acute renal failure still remains to be determined. In this study, acute renal failure (ARF) was induced in male Wistar Kyoto rats (N = 7) in a 2K/2C model of 30-minute clamping. Contractions to Ang I and II and norepinephrine (NE) were studied in isolated aortic and renal artery rings 24 hours after clamp release. Sham-operated animals served as controls (N = 7). In ARF, contractions to NE were increased in the aorta and even further enhanced in the renal artery (P < 0.05 to 0.001), whereas contractions to Ang I and II were blunted (P < 0.05). Contractions were inhibited by SQ 30741, a thromboxane A2 (TXA2)/prostaglandin H2 (PGH2) receptor antagonist. We conclude that ARF is characterized by abnormal vascular reactivity both in the renal as well as the systemic vasculature that is in part mediated by endothelium-derived vasoconstrictor prostaglandins.

How commonly are known medical conditions associated with autism?

Recent research has yielded increasing support for neurobiologic theories of autism. A number of family and twin studies support the role of genetics and have led to wide acceptance of autism as an organically based disorder. Controversy persists, however, over the role of congenital medical conditions in the etiology of autism. Two rather divergent views have emerged. One, advocated by Gillberg and colleagues, proposes that up to 30% of cases of autism are associated with a known medical condition. On the other hand, research by Rutter and colleagues suggests the incidence may be closer to 10%. In this retrospective study records on 211 subjects with autism and other developmental disorders are reviewed to determine the prevalence of associated medical conditions and its variability related to the system used to diagnose autism. Results suggest the prevalence of medical conditions with suspected etiologic relationship with autism varies between 10 and 15%, depending on the diagnostic system employed. Further variability in prevalence rates results from a less strict definition of "medical condition" and yields rates between 25 and 37%. Disparate findings in previous research may stem from variability in both diagnostic system employed and which medical conditions are considered significant in the etiology of autism.

Losartan but not verapamil inhibits angiotensin II-induced tissue endothelin-1 increase: role of blood pressure and endothelial function

Endothelin partially mediates angiotensin (Ang) II-induced vascular changes in vivo. This study investigated the effects of the angiotensin type 1 receptor antagonist losartan and the calcium channel blocker verapamil on vascular reactivity and tissue endothelin-1 levels in aortas of Wistar-Kyoto rats treated for 2 weeks with Ang II (200 ng x kg(-1) x min(-1)). Ang II increased systolic blood pressure (39+/-4 mm Hg, P<0.05). Concomitant treatment with losartan abolished the Ang II-induced pressure increase (P<0.05), whereas verapamil reduced it only partially (P<0.05). In the aortas of rats with Ang II-induced hypertension, tissue endothelin-1 content was increased threefold and contractions to endothelin-1 were impaired (P<0.05). Interestingly, these alterations were normalized by losartan (P<0.05) but not by verapamil. Hence, there was a strong, negative correlation between contractions to endothelin-1 and tissue endothelin-1 content (r=-0.733, P<0.0001). In contrast, both antihypertensive drugs normalized impaired endothelium-dependent relaxations to acetylcholine and reduced the sensitivity of vascular smooth muscle to sodium nitroprusside compared with Ang II-treated rats (P<0.05). Ang II-induced hypertension enhanced endothelium-dependent contractions to acetylcholine, and these were normalized by either drug. In conclusion, these findings suggest that long-term treatment with Ang II modulates endothelin-1 protein expression in the rat aorta. Although both antihypertensive agents lowered blood pressure and normalized endothelial function, only losartan prevented the increase in tissue endothelin-1 content, suggesting that angiotensin type 1 receptor antagonists but not calcium antagonists modulate tissue endothelin-1 in vivo.

Differential modulation of the renal and myocardial endothelin system by angiotensin II in Vivo. Effects of chronic selective ETA receptor blockade

Angiotensin II (Ang II) stimulates endothelin-1 (ET-1) production in glomerular endothelial and mesangial cells and in cardiac fibroblasts in vitro. We investigated the effects of Ang II in vivo (200 ng/kg/min for 2 weeks) with or without the ETA receptor antagonist LU135252 (50 mg/kg/day) on blood pressure, renal and myocardial ET-1 protein expression, and [125I]ET-1 uptake in male Wistar-Kyoto (WKY) rats. ET-1 was extracted from whole kidneys and ventricular myocardium and was measured by radioimmunoassay (pg ET-1/g tissue). Organ tissue uptake was calculated as percentage of total DPM recovered after i.v. administration of radiolabeled [125I]ET-1. Ang II treatment increased blood pressure by 35 +/- 3 mm Hg, which was partly reduced by LU135252 (15 +/- 2 mm Hg, p < 0.05). LU135252 in part prevented the impaired weight gain induced by Ang II (p < 0.05). Ang II induced a threefold increase in expression of ET-1 (pg/g tissue) in kidneys (from 19 +/- 2 to 58 +/- 10, p < 0.05), which was normalized by LU135252 (20 +/- 9, p < 0.05). In myocardial tissue, Ang II had only minor effects (5 +/- 1 vs. 3.6 +/- 1, n.s.). However, concomitant LU135252 treatment reduced myocardial ET-1 levels (1.4 +/- 0.4, p < 0.05 vs. Ang II and control). Ang II increased uptake of [125I]ET-1 in kidneys (from 6.9 +/- 0.1% to 10.9 +/- 0.9% of total DPM, p < 0.05) but not in myocardium (1.45 +/- 0.26% vs. 1.59 +/- 0.18% of total DPM), which was unaffected by LU135252 treatment. These data suggest that the kidney, but not the ventricular myocardium, is a target for Ang II-mediated activation of the ET system in vivo, leading to expression and uptake of ET-1. ETA antagonists may provide a new approach to inhibit production and effects of ET-1 in diseases associated with increased activity of the renin-angiotensin system.

Endothelium-independent relaxation and hyperpolarization to C-type natriuretic peptide in porcine coronary arteries

Endothelial cells produce C-type natriuretic peptide (CNP), which has been proposed as an endothelium-derived hyperpolarizing factor. In porcine coronary arteries, we investigated the vasodilatory effects of CNP and compared them with endothelium-dependent relaxations and hyperpolarizations to bradykinin. Isolated epicardial porcine coronary arteries were studied in organ chambers, and concentration-response curves to CNP and bradykinin were obtained. Membrane potential was measured in endothelial cells and smooth muscle of intact porcine coronary arteries during stimulation with CNP or bradykinin. In precontracted porcine coronary arteries with or without endothelium, CNP (10[-10]-10[-6] M) evoked relaxations (maximum, 42 +/- 4%) smaller than those evoked by bradykinin (100 +/- 1%), blunted in preparations contracted by KCl instead of U46619 (9,11-dideoxy-11a,9a-epoxymethano-prostaglandin F2alpha; p < 0.05) and unaffected by inhibition of NO synthase (NS). CNP evoked hyperpolarization of vascular smooth muscle of similar magnitude in endothelium-intact (-4.4 +/- 1 mV) and endothelium-denuded (-4.6 +/- 1 mV) porcine coronary arteries. Bradykinin (10[-10]-10[-6] M) evoked concentration-dependent relaxations in preparations with endothelium only. Although atrial natriuretic peptide-receptor antagonist HS-142-1 (25 microM) slightly reduced the sensitivity to bradykinin (log shift at IC50, twofold; p < 0.05), it had no effect on the maximal response to bradykinin. Inhibition of NO synthase partially attenuated, whereas high potassium chloride (30 mM) markedly inhibited relaxations to bradykinin (p < 0.05). Hyperpolarization to bradykinin was much more pronounced than that to CNP (-17 +/- 3 mV; p < 0.05 vs. CNP) and was observed in endothelium-intact preparations only and unaffected by HS-142-1. In conclusion, in contrast to bradykinin, CNP induces endothelium-independent and weaker relaxation and hyperpolarization of coronary artery vascular smooth muscle, suggesting that CNP is an unlikely mediator of endothelium-dependent hyperpolarization of porcine coronary arteries.

ET(A) receptor blockade prevents increased tissue endothelin-1, vascular hypertrophy, and endothelial dysfunction in salt-sensitive hypertension

Sodium plays an important role in the pathogenesis and therapy of hypertension, a major risk factor for cardiovascular disease. This study investigated the involvement of endothelin in vascular alterations in salt-induced Dahl hypertension. Salt-sensitive (DS) and salt-resistant (DR) Dahl rats were treated with a high-sodium diet (NaCl 4%) with or without ET(A) receptor antagonist LU135252 for two months, and effects of treatments on systolic blood pressure, vascular endothelin-1 (ET-1) protein content, aortic hypertrophy, and vascular reactivity of isolated aortic rings were studied. In DS rats, a high-sodium diet increased systolic pressure (190+/-4 versus 152+/-2 mm Hg, P<.05) and aortic ET-1 protein content (4.2-fold, P<.0001) and induced aortic hypertrophy as assessed by tissue weight (P<.0001). Sodium diet markedly reduced NO-mediated endothelium-dependent relaxations to acetylcholine (49+/-4% versus 81+/-4%, P<.0001) and contractions to ET-1 (92+/-7 versus 136+/-8% of KCl, P=.0011). ET-1 tissue levels were highly and inversely correlated with endothelium-dependent relaxations (r=0.931, P<.0001) and contractions to ET (r=0.77, P=.0007). LU135252 treatment reduced systolic blood pressure only in part (168+/-3 versus 190+/-4 mm Hg, P<.05) but normalized sodium-induced changes of vascular reactivity, tissue ET-1 protein content, and vascular structure (P<.001 versus sodium). None of these effects were observed in DR rats. These results suggest that ET-1 acts as a local mediator of vascular dysfunction and aortic hypertrophy in Dahl salt-induced hypertension. ET(A) receptor antagonism may have therapeutic potential for lowering vascular ET-1 content, improving endothelial function, and preventing structural changes in salt-sensitive hypertension.

Biology of the endothelium

The endothelium releases factors that control vascular relaxation and contraction, thrombogenesis and fibrinolysis, and platelet activation and inhibition. Maintaining the functional integrity of the endothelium, therefore, is critical for the preservation of blood flow and the prevention of thrombosis. This article reviews the primary endothelium-dependent substances that promote either relaxation (e.g., nitric oxide, prostacyclin) or contraction (e.g., endothelin) of blood vessels, including their physiology, mechanism of effect, and role in endothelial dysfunction. Risk factors for cardiovascular disease, such as hypertension, hypercholesterolemia, diabetes, vascular aging, and estrogen deficiency, are discussed in terms of their contributions to endothelial dysfunction, which may be the initial step in atherogenesis.

Structure and function of small arteries in salt-induced hypertension: effects of chronic endothelin-subtype-A-receptor blockade

The involvement of endothelin in salt-induced hypertension is unclear. In the Dahl rat model, we studied the effects of a selective endothelin-subtype A (ET[A]) receptor antagonist, LU135252, on blood pressure, vascular structure, and function. Dahl salt-sensitive and salt-resistant rats were treated for 8 weeks with 4% NaCl alone or in combination with LU135252 taken orally (60 mg/kg per day). The geometry and reactivity of basilar and mesenteric arteries were studied in vitro under perfused and pressurized conditions using a video dimension analyzer. Chronic salt administration increased systolic blood pressure by 37 +/- 3 mm Hg and media-lumen ratio of the basilar and mesenteric arteries in salt-sensitive rats (P<.05). These structural changes were caused by eutrophic remodeling in basilar and hypertrophic remodeling in mesenteric arteries. Endothelium-dependent relaxations to acetylcholine and contractions to endothelin-1 were impaired in mesenteric arteries of salt-sensitive rats on a high NaCl diet. LU135252 prevented part of the increase in systolic blood pressure and structural and functional alterations but increased plasma endothelin 1 levels (P<.05 versus salt-treated, saltsensitive rats). LU135252 had no effect on these parameters in salt-resistant rats. These findings suggest that the long-term pressor effect of salt administration is mediated in part by the action of endogenous endothelin acting via ET(A) receptors. Thus, chronic ET(A) receptor blockade may be useful therapeutically to lower arterial pressure and prevent endothelial dysfunction and hypertrophic remodeling of resistance arteries in salt-sensitive forms of hypertension.

Anatomic heterogeneity of vascular aging: role of nitric oxide and endothelin

We investigated the effects of aging, a cardiovascular risk factor, on vascular function with regard to endothelial nitric oxide synthase (eNOS), superoxide dismutase (SOD), and endothelin (ET-1) in aorta and femoral artery of the rat. Concentration-response curves to acetylcholine, calcium ionophore A23187, norepinephrine, ET-1, big endothelin, sodium nitroprusside, and exogenous SOD were obtained. Expression of eNOS mRNA was analyzed by reverse-transcription polymerase chain reaction, SOD activity was assessed using a chemiluminescence-based cytochrome c assay, and ET-1 plasma concentrations were measured by radioimmunoassay. In aorta of old rats, relaxations to acetylcholine and calcium ionophore A23187, basal NO release, and expression of eNOS mRNA in aortic endothelial cells were reduced (P<.05). In femoral arteries, relaxations to acetylcholine were preserved, whereas basal release of NO was attenuated (P<.05). Aging selectively increased contractions to norepinephrine and functional endothelin converting enzyme activity and attenuated contractions to ET-1 in aortas but not femoral arteries. Vascular SOD activity was higher in the femoral artery (P<.05) and unaffected by aging. Plasma ET-1 levels increased and plasma SOD activity decreased with age (P<.05). Aging was associated with an anatomic heterogeneity of endothelial dysfunction, functional endothelin converting enzyme activity, and vascular SOD activity. Vascular function was impaired in the aorta but not the femoral artery, which may be related to lower eNOS mRNA expression and SOD activity. These data suggest differential regulation of the vascular aging process that may contribute to the anatomic heterogeneity of atherosclerosis.

Angiotensin II increases vascular and renal endothelin-1 and functional endothelin converting enzyme activity in vivo: role of ETA receptors for endothelin regulation

Angiotensin II (Ang II)-stimulated expression of endothelin-1 (ET-1) mRNA is blocked by ETA antagonists in vitro. We studied effects of Ang II (200 ng/kg/min) and ETA antagonist LU135252 (50 mg/kg/d) in WKY rats in vivo investigating vascular and renal ET-1 protein expression, functional endothelin converting enzyme (ECE) activity, and clearance of (125I)ET-1. Infusion of Ang II for two weeks increased ET-1 protein content in aorta (4.7-fold) and femoral artery (1.6-fold) with and without endothelium and in kidneys (3-fold, p<0.05) and enhanced functional ECE activity (p<0.05). The Ang II-induced increase in tissue ET-1 content and functional ECE activity was completely prevented by LU135252 (p<0.05). Chronic treatment of control animals with LU135252 lowered basal vascular but not renal ET-1 content (p<0.05 vs. control). Clearance of 125IET-1 was unaffected by the treatments. It is concluded that Ang II increases ET-1 protein and functional ECE activity in vascular smooth muscle and kidney through ETA-receptors in vivo.

Angiotensin II increases tissue endothelin and induces vascular hypertrophy: reversal by ET(A)-receptor antagonist

BACKGROUND

In vitro studies on vascular smooth muscle cells suggest that endothelin has a stimulating effect on cellular proliferation. This study was designed to determine the endogenous effect of endothelin on angiotensin II-induced hypertrophy of small arteries in vivo.

METHODS AND RESULTS

Two weeks of angiotensin II administration (200 ng x kg[-1] x min[-1]) increased media thickness, media/lumen ratio, and cross-sectional area of basilar and small mesenteric arteries, confirming the proliferative properties of angiotensin II. The tissue levels of endothelin-1 were elevated in mesenteric arteries after angiotensin II administration. The administration of the selective and specific ET(A)-receptor antagonist LU135252 (50 mg x kg[-1] x d[-1]) in combination with angiotensin II prevented the changes of vascular geometry and partially reduced the increase in blood pressure induced by angiotensin II. Indeed, part of the effect on the vascular structure of the endothelin-receptor antagonist seemed pressure-independent.

CONCLUSIONS

Our results therefore demonstrate that angiotensin II increases the production of endothelin in the blood vessel wall that, via ET(A) receptors, mediates changes in vascular structure of the cerebral and mesenteric circulation. Endothelin antagonists may therefore be of value to reduce blood pressure and to prevent vascular structural changes in conditions of increased activity of the renin-angiotensin system.