Endothelial ETB Receptors Research Articles

Antecubital venous endothelial ETB receptor protein expression is preserved with aging in men.

Changes in endothelial function precede the development of cardiovascular disease (CVD). We have previously shown that age-related declines in endothelial function in women are due in part to a reduction in endothelial cell endothelin-B receptor (ETBR) protein expression. However, it is not known if ETBR protein expression changes with aging in men. The purpose of this study was to test the hypothesis that ETBR protein expression is attenuated in older men (OM) compared with younger men (YM). Primary endothelial cells were harvested from the antecubital vein of 14 OM (60 ± 6 yr; 26 ± 3 kg/m2) and 17 YM (24 ± 5 yr; 24 ± 2 kg/m2). Cells were stained with 4',6-diamidino-2-phenylindole, vascular endothelial cadherin, and ETBR. Images were quantified using immunocytochemistry. Endothelial function was assessed using brachial artery flow-mediated dilation (FMD). Systolic BP was similar (OM, 123 ± 11 vs. YM, 122 ± 10 mmHg) whereas diastolic BP was higher in OM (OM, 77 ± 7 vs. YM, 70 ± 6 mmHg; P < 0.01). Total testosterone was lower in OM (OM, 6.28 ± 4.21 vs. YM, 9.10 ± 2.68 ng/mL; P = 0.03). As expected, FMD was lower in OM (OM, 3.85 ± 1.51 vs. YM, 6.40 ± 2.68%; P < 0.01). However, ETBR protein expression was similar between OM and YM (OM, 0.39 ± 0.17 vs. YM, 0.42 ± 0.17 AU; P = 0.66). These data suggest that ETBR protein expression is not altered with age in men. These findings contrast with our previous data in women and further support sex differences in the endothelin system.NEW & NOTEWORTHY Our laboratory has previously shown that age-related declines in endothelial function are associated with a reduction in endothelial cell ETBR protein expression in women. However, it is unclear if endothelial cell ETBR protein expression is reduced with aging in men. This study demonstrates that endothelial cell ETBR protein expression is preserved with aging in men, and provides additional evidence for sex differences in the endothelin system.

Altered endothelial ETB receptor expression in postmenopausal women.

The endothelin system plays an important role in mediating vascular function. The endothelin-B receptor (ETBR) on endothelial cells mediates vasodilation via nitric oxide production. The vasodilatory effect of the ETBR is lost following menopause and may contribute to impaired vascular endothelial function in postmenopausal women (PMW). However, it is unclear if these functional changes are due to changes in ETBR expression on the endothelium. Therefore, the purpose of this study was to test the hypothesis that endothelial cell ETBR expression is lower in PMW compared with young women (YW). Primary endothelial cells were harvested from the antecubital vein of healthy PMW (n = 15, 60 ± 6 yr) and YW (n = 15, 22 ± 2 yr). Cells were identified as endothelial cells by staining for vascular endothelial cadherin, and nuclear integrity was assessed using 4',6-diamidino-2-phenylindole (DAPI). Within those cells, ETBR was quantified using immunocytochemistry; fluorescence intensity was measured in 30 cells and averaged for each participant. Endothelial function was assessed using brachial artery flow-mediated dilation (FMD). Endothelial cell ETBR expression was lower in PMW [0.46 ± 0.11 arbitrary units (AU)] compared with YW (0.58 ± 0.14 AU; P = 0.02). Furthermore, significant correlations between ETBR expression and FMD (r = 0.47, P < 0.01), total cholesterol (r = -0.38, P = 0.04), and LDL cholesterol (r = -0.39, P = 0.03) were observed. These data demonstrate that endothelial cell ETBR expression is attenuated in PMW. These novel findings provide additional insight into the mechanisms underlying vascular endothelial dysfunction in PMW.NEW & NOTEWORTHY Our study provides novel data demonstrating attenuated endothelial ETBR expression in postmenopausal women. Furthermore, our data extend current knowledge by demonstrating a positive relation between ETBR expression and brachial artery flow-mediated dilation. These findings provide additional mechanistic insight into vascular endothelial dysfunction in postmenopausal women.

Abstract P344: Increased Expression and Function of Endothelin Receptors in Aorta of (mRen2)27 Hypertensive Rats

Endothelin-1 (ET-1) contributes to various cardiovascular diseases including hypertension. ET-1 is produced in the endothelium and acts via ET A receptors, located in smooth muscle cells, and via ET B receptors, located in both endothelium and smooth muscle cells. Activation of ET A produces vasoconstriction, whereas endothelial ET B activation mediates vasodilation, with previous studies showing that ET-1-mediated vasoconstriction is enhanced in hypertension. We hypothesized that increased ETA-mediated function is present in vasculature of the (mRen2)27 hypertensive rat. Western blotting of total protein extracts from thoracic aorta was used to determine expression of ET A and ET B from Sprague-Dawley (SD n=4) and (mRen2)27 hypertensive (n=5) rats. Specificity of western blot signals for ET A and ET B was assessed by using pre-absorption of primary antibody with the corresponding antigenic peptide and intensity of signals was measured by densitometry (NIH-J Image). Contractile responses to ET-1 (10 -11 -10 -7 M) in intact and denuded aorta were determined by wire myography (Multi Myograph, DMT-USA) in the presence of the ET A blocker BQ123 (10 -6 M) or the ET B blocker BQ788 (10 -6 M). Contraction to ET-1 was expressed as maximal response (ET MAX as %K MAX ) and sensitivity (pD 2 =-Log [EC 50 ]). In aortae from (mRen2)27 rats ET A and ET B receptor expression (48 and 31 kDa bands) was greater relative to aortae of SD rats (p&lt;0.05). ET-1 contraction showed increased sensitivity in (mRen2)27 vs SD aortae (pD 2 , 8.17±0.15 vs 7.76±0.12, p&lt;0.05) with similar ET MAX (157±16 vs 145±6 %K MAX , p&gt;0.05). In intact arteries, blockade of ET B increased ET-1 sensitivity (pD 2 8.4±0.3, p&lt;0.05) in SD without effect on intact arteries from (mRen2)27 rats. In denuded arteries, ETB blockade increased ET MAX only in aortae from (mRen2)27 (205±12 vs 152±5, p&lt;0.05). Thus, increased ET A expression mediates greater ET-1-dependent contraction in vasculature of (mRen2)27 rats. In (mRen2)27 rats, loss of endothelial ET B receptor function in intact arteries may contribute to enhanced constrictor responses to ET-1, whereas increased ET B receptors in smooth muscle cells provide a counterbalancing vasodilation to offset maximal contractile effects of ET-1 in this model of hypertension.

The Effect of Hypertension on Intraocular Pressure and Apoptosis of Retinal Ganglion Cell Through ET‐1 Signaling Pathway Activation in Trabecular Meshwork of Hypertension Rat Model

PurposeTo evaluate the effect of Deoxycorticoacetate (DOCA)‐salt Hypertension model on IOP,retinal ganglion cell (RGC) apoptosis, ratio of endothelin (ET‐1)/ endothelial Nitric Oxide Synthase (eNOS), ETA and ETB Receptor (ETRA and ETRB), Myosin Light Chain Kinase (MLCK), and Caldesmon (CaD) in endothelial cells of Trabecular Meshwork (TM).MethodsExperimental study was performed on 20 male Spraque Dawley rats divided into control group(1), hypertension group (2–4): DOCA subcutaneous 10 mg/kg BW twice a week+ NaCl 0.9% daily for 2, 6, and 10 weeks respectively. Blood pressure were measured by BP analyzer with animal tail‐cuff method and IOP measured by handheld tonometry before study and before enucleation. ET‐1 signaling pathway and RGC apoptosis were evaluated by immunofluorescent staining, then observed by laser scanning confocal microscopy. Data were analyzed by one way Anova.ResultsPeak of IOP elevation occurred on 2 weeks of hypertension (7.78 ± 4.14 mmHg). The average ratio of ET‐1/eNOS was highest on 2 weeks (1.31 ± 0.025 au). The ETRA were significantly increased in 2 and 6 weeks (1476.3 ± 20.9 au and 1209.7 ± 6.1 au), while ETRB only in 2 weeks (1160.5 ± 18.2 au).The highest average of MLCK (1916.68 ± 6.41 au), CaD (1676.37 ± 7.72 au), and RGC apoptosis (576.15 ± 33.28 au) were found in 2 weeks hypertension.ConclusionsHypertension induced by DOCA‐salt stimulated significant activation of ET‐1 signaling pathway on TM, elevation of IOP, and RGC apoptosis. The peak of activation was achieved at 2 weeks of hypertension.

Role of Endothelium in Vasomotor Responses to Endothelin System and Protein Kinase C Activation in Porcine Retinal Arterioles

Endothelial cells synthesize vasodilator nitric oxide (NO) and vasoconstrictor endothelin-1 (ET-1) from NO synthase (eNOS) and endothelin-converting enzyme-1 (ECE-1), respectively. Protein kinase C (PKC) and Rho kinase (ROCK) are major signaling molecules mediating vasoconstriction. Although endothelial cells express eNOS, ECE-1, endothelin B (ET(B)) receptors, PKC, and ROCK, their influences on ET-1-induced vasoconstriction remain elusive. We studied whether these endothelial signaling molecules modulate retinal arteriolar constriction to ET-1. Porcine retinal arterioles were isolated and pressurized for vasomotor study, under conditions with intact or denuded endothelium, using videomicroscopic techniques. Retinal arterioles developed similar resting tone (≈45% of maximum diameter) with or without endothelium. Endothelial denudation attenuated vasoconstriction to ET-1 precursor, big ET-1, by almost equal to 50%, but did not affect vasoconstrictions to ET-1, ET(B) agonist sarafotoxin S6c, or PKC activator phorbol-12, 13-dibutyrate (PDBu). The ROCK inhibitor H-1152 caused vasodilation, and abolished vasoconstrictions to ET-1 and PDBu independent of endothelium. With L-type voltage-operated calcium channel (L-VOCC) blocker nifedipine, PDBu-induced vasoconstriction was abolished and converted to NO-mediated vasodilation in the presence of endothelium. The ET-1-induced vasoconstriction was unaffected by NO released from endothelium during flow elevation. Endothelial and smooth muscle ECE-1 contribute equally to synthesis of vasoactive ET-1 in retinal arterioles, with nominal role of endothelial ETB receptors in vasoconstriction to ET-1. The PKC activation leads to endothelium-dependent NO-mediated vasodilation when smooth muscle contraction is ablated by L-VOCC blockade. Endothelial cells and NO appear to have modest roles in modulating ROCK-dependent vasoconstriction, and are insufficient to counteract smooth muscle contractions to ET-1 and PKC activation.

Abstract 644: The Endothelin B Receptor Attenuates Endothelin Contraction Via An Endothelium Independent Mechanism In Mesenteric Arteries Of (mRen2)27 Rats

Endothelin-1 (ET-1) and Angiotensin II (Ang II) are important modulators of vascular tone. Contraction to ET-1 is dependent on the activation of ETA and ETB receptors. The contractile receptor ETA is localized in the smooth muscle cells whereas ETB receptors are predominantly found in the endothelium. We investigated the role of ETB receptors in ET-1 contraction in a model of Ang II-dependent hypertension, the (mRen2)27 rat. Third branch mesenteric arteries were isolated from 12 weeks old male Sprague-Dawley (SD) control and (mRen2)27 hypertensive rats and mounted on a wire Multi Myograph (Model 620, DMT) for determination of isometric force. Dose response curves to ET-1 (10 -11 -10 -7 M) were performed in arterial segments that were either intact, endothelium denuded or preincubated with the ETB specific antagonist BQ788 10 -6 M. Endothelial denudation was performed by passing a human hair through the arterial lumen and functional loss of the endothelium was confirmed by the absence of vasodilatation to acetylcholine. Maximal responses were expressed as percent of maximal response to 75mM KCl (%K MAX ) and the sensitivity as pD 2 (pD 2 = -Log[EC 50 ]). In SD control rats, addition of BQ788 significantly increased ET-1 sensitivity in intact arteries (8.9±0.1 vs 9.3±0.1, p&lt;0.05) and the increase was abolished by endothelial denudation with no change in maximal response. However, the ETB blocker BQ788 increased the maximal tension in both intact (127±2 vs 154±13 %K MAX , p&lt;0.05); and denuded (156±9 vs 188±12 %K MAX , p&lt;0.05) arteries from (mRen2)27 rats with no change in sensitivity. In summary, the present results demonstrate that endothelial ETB receptors influence vasodilatory function in control SD rats, but apparently attenuate the contraction to ET-1 in the (mRen2)27 rats. We conclude that the expression of ETB receptors in the endothelium and smooth muscle of resistance vessels in the (mRen2)27 rats may function as a compensatory mechanism to the increased blood pressure or activated angiotensin system found in this model of hypertension.

Endothelin receptors in augmented vasoconstrictor responses to endothelin‐1 in chronic intermittent hypoxia

Chronic intermittent hypoxia (CIH) contributes to the development of cardiovascular diseases in patients with obstructive sleep apnoea. Many studies have shown an association between increased circulating endothelin (ET)-1 levels and CIH. The aim of the present study was to determine the role of ET receptors in altered aortic function in an animal model of CIH. Rats were subjected to CIH (Fi o2 9% for 1min, repeated every 2min for 8h/day, 7days/week) for 3weeks. After 3weeks, the rats were killed and their aortas retrieved for use in in vitro experiments (isometric force measurement), histological analysis, immunohistochemistry and western blotting. Aortas from rats subjected to CIH exhibited marked endothelial dysfunction and increased responsiveness to ET-1. Furthermore, CIH induced increased ET-1 and ETA receptor expression, whereas ETB receptor expression was decreased. Aortic contractile responses to ET-1 were inhibited by the ETA and ETB receptor antagonists BQ-123 and BQ-788, respectively. Acetylcholine-induced relaxation responses were significantly attenuated in aortas from rats subjected to CIH, whereas CIH had no significant effect on aortic responses to sodium nitroprusside. The results of the present study suggest that increased expression of ETA receptors, which mediate a potent vasoconstrictor response, plays an important role in the pathogenesis of CIH. In addition, decreased endothelial ETB receptor expression, which is associated with the functional decline of endothelium-dependent vasodilation, also contributes to the pathogenesis of CIH. It appears that the ETB receptor-induced buffering of ET-1 responsiveness is mediated via a nitric oxide-dependent mechanism.

Age-associated alterations in retinal arteriole reactivity to endothelin-1 differ between the sexes

Endothelin-1 (ET-1) is a vasoconstrictor implicated in age-related retinal pathologies. This study determined whether responses to ET-1 differed in retinal arterioles isolated from adult (2–3 months) and aged (>20 months) Fischer 344 rats of both sexes. Risk factors for retinal disease (retinal perfusion pressure, intraocular pressure, blood glucose) were not affected by age. However, sensitivity to ET-1 declined with age, especially in females. Vasoconstrictor responses to 50mM KCl and Ca2+ release by caffeine (10mM) were similar in all groups. Retinal ETA and ETB receptor expression also was similar in young and aged rats, regardless of sex. Contractions elicited by 10nM ET-1 were inhibited by the ETA antagonist BQ-123 (1μM) in all groups. In contrast, the ETB antagonist BQ-788 (1μM) restored ET-1-induced contractions in aged female vessels, but had no effect in any other group. Removal of the endothelium also restored contractions in vessels from aged females but not males. Thus, responsiveness to ET-1 declines with age in retinal microvasculature. In males, this is likely mediated by age-related changes in the ETA receptor signaling pathway. By contrast, effects of ET-1 on endothelial ETB receptors attenuate vasoconstrictor responses in aged females.

Comparison of endothelin receptors in normal versus cirrhotic human liver and in the liver from endothelial cell-specific ETB knockout mice

AimsEndothelin (ET) antagonists show promise in animal models of cirrhosis and portal hypertension. The aim was to pharmacologically characterise the expression of endothelin receptors in human liver, hepatic artery and portal vein. Main methodsImmunofluorescence staining, receptor autoradiography and competition binding assays were used to localise and quantify ET receptors on hepatic parenchyma, hepatic artery and portal vein in human cirrhotic or normal liver. Additional experiments were performed to determine the affinity and selectivity of ET antagonists for liver ET endothelin receptors. An endothelial cell ETB knockout murine model was used to examine the function of sinusoid endothelial ETB receptors. Key findingsETB receptors predominated in normal human liver and displayed the highest ratio (ETB:ETA 63:47) compared with other peripheral tissues. In two patients examined, liver ETB expression was up-regulated in cirrhosis (ETB:ETA 83:17). Both sub-types localised to the media of normal portal vein but ETB receptors were downregulated fivefold in the media of cirrhotic portal vein. Sinusoid diameter was fourfold smaller in endothelial cell ETB knockout mice. The liver morphology of ETB knockout mice was markedly different to normal murine liver, with loss of the wide spread sinusoidal pattern. In the knockout mice, sinusoids were reduced in both number and absolute diameter, while large intrahepatic veins were congested with red blood cells. SignificanceThese data support a role for the ET system in cirrhosis of the liver and suggest that endothelial ETB blockade may cause sinusoidal constriction which may contribute to hepatotoxicity associated with some endothelin antagonists.

Modulators of the Vascular Endothelin Receptor in Blood Pressure Regulation and Hypertension

Endothelin (ET) is one of the most investigated molecules in vascular biology. Since its discovery two decades ago, several ET isoforms, receptors, signaling pathways, agonists and antagonists have been identified. ET functions as a potent endothelium-derived vasoconstrictor, but could also play a role in vascular relaxation. In endothelial cells, preproET and big ET are cleaved by ET converting enzymes into ET-1, -2, -3 and -4. These ET isoforms bind with different affinities to ETA and ETB receptors in vascular smooth muscle (VSM), and in turn increase [Ca2+]i, protein kinase C and mitogen-activated protein kinase and other signaling pathways of VSM contraction and cell proliferation. ET also binds to endothelial ETB receptors and stimulates the release of nitric oxide, prostacyclin and endothelium-derived hyperpolarizing factor. ET, via endothelial ETB receptor, could also promote ET re-uptake and clearance. While the effects of ET on vascular reactivity and growth have been thoroughly examined, its role in the regulation of blood pressure and the pathogenesis of hypertension is not clearly established. Elevated plasma and vascular tissue levels of ET have been identified in saltsensitive hypertension and in moderate to severe hypertension, and ET receptor antagonists have been shown to reduce blood pressure to variable extents in these forms of hypertension. The development of new pharmacological and genetic tools could lead to more effective and specific modulators of the vascular ET system for treatment of hypertension and related cardiovascular disease. Keywords: Blood pressure, calcium, endothelium, nitric oxide, smooth muscle, Hypertension, ET Receptor-Mediated Signaling

Basic Science of Pulmonary Arterial Hypertension for Clinicians

Pulmonary arterial hypertension (PAH) is a syndrome in which pulmonary arterial obstruction increases pulmonary vascular resistance, which leads to right ventricular (RV) failure and a 15% annual mortality rate. The present review highlights recent advances in the basic science of PAH. New concepts clarify the nature of PAH and provide molecular blueprints that explain how PAH is initiated and maintained. Five basic science concepts provide a framework to understand and treat PAH: (1) Endothelial dysfunction creates an imbalance that favors vasoconstriction, thrombosis, and mitogenesis. Restoration of this balance by inhibition of endothelin and thromboxane or augmentation of nitric oxide (NO) and prostacyclin is the paradigm on which most current therapy is based. (2) PAH has a genetic component. Mutations (bone morphogenetic protein receptor-2 [BMPR2]) and single-nucleotide polymorphisms (SNPs; ion channels and transporter genes) predispose to PAH. (3) Excess proliferation, impaired apoptosis, and glycolytic metabolism in pulmonary artery smooth muscle, fibroblasts, and endothelial cells suggest analogies to cancer. Many experimental therapies reduce PAH by decreasing the proliferation/apoptosis ratio; these include inhibitors of pyruvate dehydrogenase kinase (PDK), serotonin transporters (SERT), survivin, 3-hydroxy-3-methylglutaryl coenzyme A reductase, transcription factors (hypoxia-inducible factor [HIF]-1α and nuclear factor of activated T lymphocytes [NFAT]), and tyrosine kinases. Augmentation of voltage-gated K+ channels (Kv1.5) and BMPR2 signaling also addresses this imbalance. Tyrosine kinase inhibitors used to treat cancer are currently in phase 1 PAH trials. (4) Refractory vasoconstriction may occur due to rho kinase activation. Fewer than 20% of PAH patients respond to conventional vasodilators; however, refractory vasoconstriction may respond to rho kinase inhibitors. (5) The RV can be targeted therapeutically. Although increased afterload initiates RV failure, which is the major cause of death/dysfunction in PAH, the RV may be amenable to cardiac-targeted therapies. The RV in PAH has features of ischemic, hibernating myocardium. Guided by these new …

Working under pressure: coronary arteries and the endothelin system

Endogenous endothelin-1-dependent (ET-1) tone in coronary arteries depends on the balance between ET(A) and ET(B) receptor-mediated effects and on parameters such as receptor distribution and endothelial integrity. Numerous studies highlight the striking functional interactions that exist between nitric oxide (NO) and ET-1 in the regulation of vascular tone. Many of the cardiovascular complications associated with cardiovascular risk factors and aging are initially attributable, at least in part, to endothelial dysfunction characterized by a dysregulation between NO and ET-1. The contribution of the imbalance between smooth muscle ET(A/B) and endothelial ET(B) receptors to this process is poorly understood. An increased contribution of ET-1 that is associated with a proportional decrease in that of NO accompanies the development of coronary endothelial dysfunction, coronary vasospasm, and atherosclerosis. These data form the basis for the rationale of testing therapeutic approaches counteracting ET-1-induced cardiovascular dysfunction. It remains to be determined whether the beneficial role of endothelial ET(B) receptors declines with age and risk factors for cardiovascular diseases, revealing smooth muscle ET(B) receptors with proconstricting and proinflammatory activities.

Endothelin-1 Impairs Alveolar Epithelial Function via Endothelial ETB Receptor

Endothelin-1 (ET-1) is increased in patients with high-altitude pulmonary edema and acute respiratory distress syndrome, and these patients have decreased alveolar fluid reabsorption (AFR). To determine whether ET-1 impairs AFR via activation of endothelial cells and nitric oxide (NO) generation. Isolated perfused rat lung, transgenic rats deficient in ETB receptors, coincubation of lung human microvascular endothelial cells (HMVEC-L) with rat alveolar epithelial type II cells or A549 cells, ouabain-sensitive 86Rb+ uptake. The ET-1-induced decrease in AFR was prevented by blocking the endothelin receptor ETB, but not ETA. Endothelial-epithelial cell interaction is required, as direct exposure of alveolar epithelial cells (AECs) to ET-1 did not affect Na,K-ATPase function or protein abundance at the plasma membrane, whereas coincubation of HMVEC-L and AECs with ET-1 decreased Na,K-ATPase activity and protein abundance at the plasma membrane. Exposing transgenic rats deficient in ETB receptors in the pulmonary vasculature (ET-B(-/-)) to ET-1 did not decrease AFR or Na,K-ATPase protein abundance at the plasma membrane of AECs. Exposing HMVEC-L to ET-1 led to increased NO, and the ET-1-induced down-regulation of Na,K-ATPase was prevented by the NO synthase inhibitor l-NAME, but not by a guanylate cyclase inhibitor. We provide the first evidence that ET-1, via an endothelial-epithelial interaction, leads to decreased AFR by a mechanism involving activation of endothelial ETB receptors and NO generation leading to alveolar epithelial Na,K-ATPase down-regulation in a cGMP-independent manner.

Inhalation of endothelin receptor blockers in pulmonary hypertension

Endothelin 1 (ET-1) is a potent pulmonary vasoconstrictor and mediator of lung diseases. Antagonism of the ET-1-mediated effects has become an important therapeutic approach. ET-1 (A and B) receptors are differentially distributed in the lung vasculature. Whereas the ET(A) receptors mainly mediate vasoconstriction, the endothelial ET(B) receptor seems to have vasodilative properties. We sought to determine if antagonism of ET receptors can be achieved by inhalation of specific blockers in a model of ET-1-mediated pulmonary hypertension.

Endothelin 1 Decreases Lung Edema Clearance in Alveolar Epithelial Cells via Endothelial Et-B Receptor Activation and Nitric Oxide Generation

Restricted accessAbstractFirst published March 2007Endothelin 1 Decreases Lung Edema Clearance in Alveolar Epithelial Cells via Endothelial Et-B Receptor Activation and Nitric Oxide GenerationA. Comellas, A. Briva, […], M. Butti, J. Chen, J. Litvan, Z. Azzam, E. Lecuona, L. Pesce, M. Yanagisawa, and J.I. Sznajder+7-7View all authors and affiliationsVolume 55, Issue 2https://doi.org/10.1177/108155890705500232

Renal function during normal pregnancy and preeclampsia

Glomerular filtration rate and renal plasma flow increase by 40 to 65 and 50 to 85%, respectively, during normal pregnancy in women. Studies using the gravid rat as a model have greatly enhanced our understanding of mechanisms underlying these remarkable changes in the renal circulation during gestation. Hyperfiltration is largely due to increased renal plasma flow, the latter attributable to profound reductions in both the renal afferent and efferent arteriolar resistances. The ovarian hormone, relaxin, mediates renal vasodilation during pregnancy. Relaxin increases vascular gelatinase activity, thereby converting big ET to ET(1-32), which leads to renal vasodilation, hyperfiltration and reduced myogenic reactivity of small renal arteries via the endothelial ET(B) receptor and nitric oxide. Serum concentration of uric acid falls during normal pregnancy as a consequence of increased GFR and/or reduced proximal tubular reabsorption. The elevated urinary excretion of protein during pregnancy is secondary to increased GFR, reduced proximal tubular reabsorption, and perhaps alteration in the electrostatic charge of the glomerular filter. Whether the tubular secretion of Tamm-Horsfall protein increases during normal pregnancy is uncertain. In most women with preeclampsia, renal plasma flow and glomerular filtration rate are at most only modestly decreased as a consequence of increased afferent arteriolar resistance and/or reduced ultrafiltration coefficient. Serum uric acid concentrations are increased mainly as a consequence of reduced renal clearance. Reduced GFR leads to decreased filtered load of uric acid, and plasma volume contraction contributes to increased proximal tubular reabsorption coupled to sodium. The increase in urinary protein excretion in preeclampsia occurs secondary to alterations in the size and/or charge selectivity of the glomerular filter, possible increases in glomerular capillary pressure, and compromise of proximal tubular reabsorption. The renal histologic lesion characteristic of preeclampsia is termed "glomerular endotheliosis". Recent evidence suggests that anti-angiogenic factors emanating from the placenta in preeclampsia contribute to glomerular endotheliosis, proteinuria, and hypertension during disease.

Endothelin receptors as drug targets in chronic cardiovascular diseases: the rationale for dual antagonism

AbstractEndothelin has been described as the most potent vasoconstrictor known. Recent research shows that it is also a growth factor, a promoter of fibrosis and inflammation, and a key initiator of endothelial dysfunction. Endothelin becomes, therefore, a candidate in the pathogenesis of many chronic cardiovascular and fibrotic diseases, and inhibition of endothelin function is a potential therapeutic approach for those diseases. Endothelin receptor antagonists are now established therapy in the treatment of pulmonary arterial hypertension, and present promising perspectives in diabetic nephropathy, peripheral arterial disease, hypertension, heart failure, and pulmonary diseases. Endothelin binds to two endothelin receptors, ETA and ETB, and their respective roles are actively debated. A major challenge lies in the understanding of what is the preferred profile for new drugs: selective ETA antagonism or dual ETA and ETB receptor antagonism. A number of cardiovascular diseases are characterized by an up‐regulation of smooth muscle cell ETB receptors mediating vasoconstriction and proliferation, and a down‐regulation of endothelial ETB receptors, as compared to the physiological state, creating a situation where both ETA and ETB receptors contribute to vasoconstriction and remodeling. When these two receptor subtypes co‐exist, a cross‐talk between them, probably a result of receptor heterodimerization, suggests that dual ETA/ETB receptor antagonism may be necessary to obtain maximal efficacy. Drug Dev. Res. 67:825–834, 2006. © 2007 Wiley‐Liss, Inc.

ETBreceptor dependent alteration in aortic responses to ET-1 in the cardiomyopathic hamsterThis paper is one of a selection of papers published in this Special issue, entitled Second Messengers and Phosphoproteins—12th International Conference.

The aim of this study was to verify whether an alteration in the aortic endothelin-1 (ET-1) response takes place in UM-X7.1 cardiomyopathic hamsters. Our results showed that ET-1 (10(-12) - 10(-5) mol/L) induces dose-dependent sustained increases in tension in the intact and endothelium denuded aortas from both normal and cardiomyopathic hamsters. The EC50 values of ET-1 of both intact and endothelium denuded aortas of normal hamsters were similar (2.2 x 10(-9) mol/L and 1.8 x 10(-9) mol/L, respectively). However, in cardiomyopathic hamsters, the EC50 of ET-1 in intact aortas was higher (1.5 x 10(-8) mol/L) than that of the endothelium denuded preparations (2.7 x 10(-9) mol/L). The EC50 of ET-1 in normal and cardiomyopathic hamster denuded aortas were similar. However, the EC50 of ET-1 in intact aortas of cardiomyopathic hamster was higher (1.5 x 10(-8) mol/L) than that of normal hamsters (2.2 x 10(-9) mol/L). Pre-treatment with the ETA receptor antagonist ABT-627 (10(-5)mol/L) of intact and endothelium denuded aortas from both normal and cardiomyopathic hamsters significantly prevented ET-1 (10(-7) mol/L) from inducing an increase in tension. Pre-treatment with the ETB receptor antagonist A-192621 (10(-5) mol/L) had no effect on the ET-1-induced increase in tension in endothelium denuded aortas of both normal and cardiomyopathic hamsters, as well as in intact preparations of normal animals. However, blockade of the ETB receptors in intact aortas of cardiomyopathic hamsters significantly (p < 0.001) potentiated the ET-1-induced increase in tension. In summary, an attenuation of the contraction response to ET-1 was found in UM-X7.1 cardiomyopathic hamsters when compared with normal age-matched hamsters. This alteration of the ET-1 effect in the aortas of cardiomyopathic hamsters seems to be dependent on the presence of the endothelium and could be due, in part, to an increase in the contribution of endothelial ETB receptors to relaxation, which in turn acts as a physiological depressor of ET-1 vasoconstriction. Our results suggest that an increase in the endothelium ETB receptor density may play a role in the development of hypotension in UM-X7.1 cardiomyopathic hamsters.

The role of endothelin-1 in vascular remodeling in vivo

See article by Dao et al. [4] (pages 61–68) in this issue. Vascular smooth muscle cells (VSMCs) are a major component of the arterial wall and play a critical role in the development of occlusive vascular lesions. In normal vessels, VSMCs are quiescent, differentiated, and contractile and function to maintain vascular tone and blood pressure. In pathological processes such as the response to vascular injury, VSMCs undergo a phenotypic transition whereby they proliferate, migrate from the medial to the intimal layer, and lead to neointimal formation and subsequent vascular remodeling. These resultant vascular changes contribute to the pathological basis of atherosclerosis and restenosis that occur after revascularization procedures such as angioplasty, stenting, and bypass grafting. Endothelin-1 (ET-1) is a potent 21-amino acid vasoconstrictor peptide. ET-1 is mainly generated from the endothelium of blood vessels and functions in a paracrine or autocrine manner on ETA and ETB receptors. These receptors present on VSMCs have been shown to induce contraction and stimulate cell hypertrophy and/or hyperplasia, while endothelial ETB receptors stimulate the production of nitric oxide and prostacyclin and accordingly elicit vasorelaxation. Accumulating evidence indicates that endogenous ET-1 is involved in the vascular remodeling in cardiovascular diseases. For example, local ET-1 production has been shown to be increased in vascular lesions, in neointimal formation after vascular injury, and in atherosclerosis, hypercholesterolemia, and hypertension. Indeed, the administration of ET receptor antagonists reduced the neointimal formation after vascular injury and prevented vascular remodeling in deoxycorticosterone acetate (DOCA)-salt hypertensive rats; this suggested the possibility that ET-1 induces VSMC hyperplasia in this process in vivo. However, several studies using cultured VSMCs showed that ET-1 stimulates VSMC hypertrophy but not hyperplasia in vitro [1–3]. Therefore, it is necessary to develop an understanding of the effect of ET-1 on VSMC hypertrophy and/or hyperplasia in vivo. In the current issue of Cardiovascular Research, Dao et al. [4] have examined the mitogenic or trophic effect of ET-1 in rat small mesenteric arteries in vivo and demonstrated that administration of low doses of ET-1 stimulated protein synthesis (hypertrophy) in the arteries, whereas high doses stimulated both protein and DNA synthesis (hyperplasia).

Etiology-Specific Endothelin-1 Clearance in Human Precapillary Pulmonary Hypertension

Endothelin (ET)-1 is a mediator of vascular remodeling seen in human pulmonary hypertension (PH), and it is normally cleared via endothelial ET-B receptors. Increased levels of ET-1 are found in precapillary PH, partly from increased synthesis. We hypothesized that the endothelial dysfunction and vascular remodeling seen in human precapillary PH would also reduce ET-1 clearance. Case series from a single institutional PH center. Thirty-four patients with pulmonary arterial hypertension (PAH; idiopathic [IPAH], n = 19; connective tissue disease [CTD], n = 15) and 11 patients with chronic thromboembolic PH were studied. Using indicator dilution methods, the first-pass extraction of radiolabeled ET-1 through the pulmonary circulation, and permeability surface (PS) area, an index of functional microvascular surface available for ET-1 clearance, were determined. Mean extraction for IPAH and thromboembolic PH groups was normal, but it was reduced in PAH from CTD; 69% of all patients studied had normal extraction. The mean PS product was reduced significantly for all three etiologies as compared to normal, but 58% of IPAH patients and 40% of CTD-related PAH patients had normal PS products. Receptor-mediated ET-1 extraction and functional vascular surface area for clearance vary between etiologies of PAH. However, contrary to our hypothesis, endothelial ET-B receptor-mediated extraction is preserved in many patients. The scientifically significant finding of our study is that high ET-1 levels seen in patients with PAH must be predominantly due to excess synthesis rather than reduced clearance. The finding that endothelial ET-B receptors are still present and functional in PAH may also be of relevance to the choice of selective vs nonselective ET receptor antagonists.