Renal and vascular effects of chronic endothelin receptor antagonism in malignant hypertensive rats

The effect of the combined ET_A/ET_B endothelin receptor antagonist bosentan on blood pressure, vascular hypertrophy, and pathologic renal changes was investigated in a model of malignant hypertension, severe vascular hypertrophy, and enhanced vascular expression of endothelin-1, the deoxycorticosterone acetate (DOCA), and salt-treated spontaneously hypertensive rat (SHR). DOCA-salt treated SHR received 100 mg bosentan per kilogram weight per day mixed with their food. Systolic blood pressure of untreated DOCA-salt SHR rose to 241 ± 1.5 mm Hg, whereas that of bosentan-treated rats rose to 221 ± 5.1 mm Hg (P < .01). Cardiac and conduit artery mass were not affected by treatment. Small arteries from the coronary, renal, and mesenteric circulations showed a smaller media width and cross-sectional area of the media in rats treated with bosentan than in untreated rats. The kidneys showed the presence of fibrinoid necrosis in a high percentage of afferent arterioles and glomeruli of untreated DOCA-SHR. Some kidneys of treated rats exhibited less severe vascular hypertrophy and lesser extent of vascular or glomerular fibrinoid necrosis, but the renal injury score of bosentan-treated DOCA-SHR was only at the limit of significance from that of untreated rats (P = .06). These results suggest a role for endothelin-1 in blood pressure elevation and the severe vascular hypertrophy of small arteries of the coronary, renal, and mesenteric vasculature, but not of the heart or larger conduit vessels in the malignant hypertension that SHR develop after treatment with DOCA and salt. Although some bosentan-treated rats showed fewer renal lesions, a significant effect on renal pathology could not be unambigously demonstrated. Further studies will be necessary to determine whether endothelin antagonists may indeed offer some degree of renal protection and have therapeutic potential in severe or malignant hypertension.     

Acute hemodynamic and neurohumoral effects of selective ETA receptor blockade in patients with congestive heart failure

OBJECTIVESTo investigate the hemodynamic effects of the selective endothelin (ET)_A receptor antagonist LU135252 in patients with congestive heart failure (CHF).BACKGROUNDNonselective ET_A/B receptor antagonists improve hemodynamics in patients with CHF. Since ET_B receptors mediate the release of nitric oxide and the clearance of ET-1, selective ET_A antagonists are of special interest.METHODSThe hemodynamic effects of a single oral dose of the selective ET_A receptor antagonist LU135252 (1, 10, 30, 100 or 300 mg) were investigated in a multicenter study involving 95 patients with CHF (New York Heart Association II–III) with an ejection fraction ≤35%.RESULTSBaseline ET-1 positively correlated with pulmonary vascular resistance, pulmonary capillary wedge pressure (PCWP), and mean pulmonary artery pressure (MPAP, r = 0.37–0.50, p < 0.0004) but were inversely related to cardiac index (CI; r = −0.36, p = 0.0004). LU135252 dose dependently increased CI and decreased mean arterial pressure and systemic vascular resistance (p < 0.03–0.0002), while heart rate remained constant or decreased slightly. Pulmonary capillary wedge pressure, MPAP, pulmonary vascular resistance and right atrial pressure also decreased significantly (p < 0.035–< 0.0001). Two hours after LU135252, plasma ET-1 did not significantly increase after 1 mg but did so by 23% (p = 0.003), 29% (p = 0.0018), 56% (p < 0.0001) and 101% (p < 0.0001) after 10, 30, 100 and 300 mg, respectively, while plasma catecholamines remained constant.CONCLUSIONSIn patients with CHF, a single oral dose of the selective ET_A receptor antagonist LU135252 improves hemodynamics in a dose-dependent manner without activation of other neurohumoral systems and is well tolerated over a wide dose range.     

Endothelin Antagonism in Experimental Ischemic Heart Failure: Hemodynamic, Structural and Neurohumoral Effects

Heart failure is characterized both by an activation of the endothelin system and an increased vasoconstrictor contractile response to the peptide. Given its pharmacological profile, it is likely that endothelin (ET-1) plays a deleterious role in the development of heart failure, and that blockers of the endothelin system are beneficial in this disease. Indeed, in rats with heart failure, ET_A and dual ET_A-ET_B receptor antagonists reduce arterial pressure as well as left ventricular end diastolic pressure. The same antagonists also prevent the degradation of left ventricular function, as evidenced by the increased left ventricular fractional shortening and wall thickening. ET_A and ET_A-ET_B antagonists also reduce LV dilatation and LV fibrosis, but do not affect LV hypertrophy. Moreover, comparison between selective ET_A and combined ET_A-ET_B antagonists reveal no differences in terms of their effects on blood pressure, LV hemodynamics or remodeling. However, only combined ET_A-ET_B antagonists significantly decreased heart rate. ET_B antagonists alone do not affect blood pressure or LV hemodynamics, but reduce LV fibrosis.With regard to survival, we have shown that long term treatment with the dual ET_A-ET_B antagonist bosentan increased survival to the same extent as an angiotensin converting enzyme inhibitor. However, the effect of selective ET_A antagonists on survival is more controversial, since we found that the non-peptide ET_A antagonists LU 135252 did not affect survival of rats with myocardial infarction, while others have shown that the peptide ET_A antagonist BQ-123 increased survival in the same model. These conflicting data regarding the efficacy of selective ET_A vs dual ET_A-ET_B blockade points out the need for controlled long term studies comparing the effects of theses two pharmacological approaches on survival.     

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 ET_A 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 ET_A 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 μmol/liter, P < 0.01). Treatment with the ET_A 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 μmol/liter, P < 0.05). Chronic ET_A 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 ET_A 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. ET_A receptor blockade may have therapeutic potential in patients with atherosclerosis.     

Endothelin-A Receptor Antagonism during Acute Myocardial Infarction in Rats

Endothelin levels are increased in rats with experimentally induced myocardial infarction. The purpose of this study was to determine whether endothelin-A (ET_A) receptor antagonism alters ventricular remodeling and the development of heart failure after myocardial infarction (MI). We administered 10 mg/kg/day of A-127722 to rats post-MI for 6 weeks. A hemodynamic study was performed and passive pressure-volume curves obtained. In rats without infarcts, ET_A receptor antagonist (n=8; vehicle, n = 5) had no effect. However, in rats with infarcts ET_A antagonism (n = 14, MI = 35%; vehicle: n = 19, MI = 32%) reduced systemic arterial and LV systolic (but not end-diastolic) pressures and shifted the pressure-volume relationship to the right. Because LV mass was not changed, the volume-to-mass ratio was increased and was correlated inversely with the ability of the LV to maximally develop pressure. This increase in volume at low distending pressures was also coupled with a tendency (P < 0.06) for reduced scar thickness, suggesting that early initiation of an ET_A receptor antagonism increased infarct expansion. The reduction in blood pressure offset the increase in volume such that wall stresses were unchanged, as was LV mass. The early use of ET_A receptor antagonism in the rat model of myocardial infarction did not beneficially alter LV remodeling.     

Change in pharmacological effect of endothelin receptor antagonists in rats with pulmonary hypertension: Role of ETB-receptor expression levels

Background and purposeThe endothelin (ET) system is activated in pulmonary arterial hypertension (PAH). The therapeutic value of pharmacological blockade of ET receptors has been demonstrated in various animal models and led to the current approval and continued development of these drugs for the therapy of human PAH. However, we currently incompletely comprehend what local modifications of this system occur as a consequence of PAH, particularly in small resistance arteries, and how this could affect the pharmacological response to ET receptor antagonists with various selectivities for the receptor subtypes. Therefore, the purposes of this study were to evaluate potential modifications of the pharmacology of the ET system in rat pulmonary resistance arteries from monocrotaline (MCT)-induced pulmonary arterial hypertension.Experimental approachET-1 levels were quantified by ELISA. PreproET-1, ET_A and ET_B receptor mRNA expressions were quantified in pulmonary resistance arteries using Q-PCR, while protein expression was evaluated by Western blots. Reactivity to ET-1 of isolated pulmonary resistance arteries was measured in the presence of ET_A (A-147627), ET_B (A-192621) and dual ET_A/B (bosentan) receptor antagonists.Key resultsIn rats with PAH, plasma ET-1 increased (p < 0.001) while pulmonary levels were reduced (p < 0.05). In PAH arteries, preproET-1 (p < 0.05) and ET_B receptor (p < 0.001) gene expressions were reduced, as were ET_B receptor protein levels (p < 0.05). ET-1 induced similar vasoconstrictions in both groups. In arteries from sham animals, neither bosentan nor the ET_A or the ET_B receptor antagonists modified the response. In arteries from PAH rats, however, bosentan and the ET_A receptor antagonist potently reduced the maximal contraction, while bosentan also reduced sensitivity (p < 0.01).Conclusions and implicationsThe effectiveness of both selective ET_A and dual ET_A/B receptor antagonists is markedly increased in PAH. Down-regulation of pulmonary resistance arteries ET_B receptor may contribute to this finding.     

Inhibitory effects of PPAR-γ on endothelin-1-induced inflammatory pathways in vascular smooth muscle cells from normotensive and hypertensive rats

The present study evaluated the effects of endothelin (ET)-1 and the peroxisome proliferator activated receptor γ (PPAR-γ) agonist, rosiglitazone, on inflammatory markers in vascular smooth muscle cells (VSMCs) from normotensive (WKY) and hypertensive (SHRSP) rats. Rat VSMC-derived mesenteric arteries from WKY and SHRSP were treated with ET-1 (100 mmol/L) and rosiglitazone (1μmol/L) or ET type A (ET_A) or type B (ET_B) receptor antagonists. Nuclear factor kappa-B (NFκB) binding activity was assessed by electrophoretic mobility shift assay and phospho-inhibitory κB (IκB); vascular cell adhesion molecule (VCAM)-1, intercellular adhesion molecule (ICAM)-1, and cyclooxygenase (COX)-2 expression was determined using Western blotting. ET-1 significantly increased NFκB binding, and VCAM-1, ICAM, and COX-2 expression to a greater degree in SHRSP than in WKY VSMC. These changes were associated with increased phosphorylation of IκB, thus resulting in decreased NFκB inhibition. Co-incubation with PPAR-γ activator rosiglitazone, or ET_A or ET_B receptor antagonism prevented ET-1-stimulated vascular proinflammatory effects in both WKY and SHRSP VSMC. Proinflammatory effects of ET-1 in VSMCs are mediated via both ET_A and ET_B receptor subtypes. These effects may be abrogated by the PPAR-γ activator rosiglitazone. PPAR-γ activators may thus prevent deleterious ET-1-dependent proinflammatory vascular effects in VSMC in hypertension.     

内皮素受体拮抗剂BMS-182874对高血压大鼠左心室和冠状动脉壁的影响

目的：研究内皮素受体Ａ（ＥＴＡ ）拮抗剂ＢＭＳ－１８２８７４ 对高血压大鼠左心室肥厚和冠状动脉管壁增厚的影响。　　方法：研究于１９９７ 年１月～５ 月完成。４ 周龄大鼠设３组：分别为自发性高血压大鼠（ＳＨＲ组）、ＳＨＲ口服ＢＭＳ－１８２８７４（ＳＨＲ＋ Ｂ组）和正常血压大鼠（ＷＫＹ组），饲养１２周。　　结果：ＳＨＲ＋ Ｂ组与ＳＨＲ组比较，收缩压、左心室重与体重比、冠状动脉外径大于１００ μｍ 的冠状动脉管壁横截面积及横截面积与内径比、平滑肌细胞的宽度及最大冠状动脉流量均无显著差异；冠状动脉外径小于１００ μｍ 的冠状动脉管壁横截面积及横截面积与内径比，ＳＨＲ＋ Ｂ组较ＳＨＲ组显著下降。血浆和心肌的ＥＴ含量：ＳＨＲ组与ＷＫＹ组无显著差异，ＳＨＲ＋ Ｂ组显著下降。　　结论：ＥＴＡ 拮抗剂ＢＭＳ－１８２８７４治疗能部分预防ＳＨＲ外径小于１００ μｍ 冠状动脉管壁的增厚，但对ＳＨＲ大鼠高血压的形成、左心室和外径大于１００ μｍ 冠状动脉管壁的增厚及平滑肌细胞的肥大无明显的影响。     

Prolonged Anti-Hypertensive Effects of Oral Sitaxsentan, a Selective ETA Endothelin Receptor Antagonist, in Spontaneoulsy Hypertensive Hamsters

Introduction The purpose of this study was to determine whether prolonged oral therapy with sitaxsentan, a potent selective ET_A endothelin receptor antagonist, normalizes systolic blood pressure in spontaneously hypertensive hamsters, a new rodent model of high-renin genetic hypertension. Materials and Methods Spontaneously hypertensive hamsters received either oral sitaxsentan (15 mg kg⁻¹ day⁻¹) dissolved in high purity water or saline for 7 weeks. Systolic blood pressure was monitored in lightly anesthetized animals using the leg-cuff method. Results We found that sitaxsentan elicited a significant decrease in systolic blood pressure in spontaneously hypertensive hamsters from 175 ± 6 mmHg at baseline to 109 ± 7 mmHg after 7 weeks (p < 0.05). Although treatment of spontaneously hypertensive hamsters with saline was also associated with a significant decrease in systolic blood pressure from baseline, the magnitude of response was significantly less than that observed with sitaxsentan (p < 0.05). Discussion Collectively, these proof-of-principle data indicate that prolonged oral sitaxsentan therapy normalizes systolic blood pressure in spontaneously hypertensive hamsters. We suggest that selective ET_A endothelin receptor blockade could be beneficial in the treatment of essential hypertension associated with high renin plasma levels.     

Myocardial fibrosis in DOCA-salt hypertensive rats: effect of endothelin ET(A) receptor antagonism

BACKGROUND: To test the hypothesis that endothelin-1 contributes to cardiac fibrosis, cardiac collagen deposition was studied in deoxycorticosterone acetate-salt (DOCA-salt) hypertensive rats, in which the endothelin system is activated. The effects of the ET(A)-selective endothelin receptor antagonist A-127722 were evaluated. METHODS AND RESULTS: A-127722 (30 mg/kg per day) was administered for 4 weeks. Myocardial fibrosis was evaluated after Sirius red F3BA staining. Systolic blood pressure was 103+/-1.6 mm Hg in unilaterally nephrectomized rats (Uni-Nx), 202+/-3.2 mm Hg in DOCA-salt rats (P:<0.01 versus Uni-Nx), and 182+/-3.1 mm Hg in ET(A) antagonist-treated DOCA-salt rats (P:<0.01 versus DOCA-salt or Uni-Nx). In DOCA-salt rats, interstitial and perivascular collagen density was increased in the subendocardial and midmyocardial regions of the left ventricle (3- to 4-fold, P:<0.05), whereas in subepicardial myocardium, the increase was predominantly perivascular. The ET(A) antagonist prevented cardiac fibrosis in DOCA-salt rats. Procollagen I and III mRNA, which were increased in hearts of DOCA-salt rats, were normalized by ET(A) antagonist treatment. TGF-beta(1) mRNA and TGF-beta(1) protein increased at 1 week in DOCA-salt rats and were lowered in ET(A) antagonist-treated rats. CONCLUSIONS: ET(A) receptor-mediated collagen deposition in hearts of DOCA-salt rats results from increased procollagen synthesis associated with an initial increment in expression of TGF-beta(1). These results support the hypothesis of a role for endothelin-1 in cardiac collagen deposition in mineralocorticoid hypertension, which may have pathophysiological and pharmacological implications in hypertensive heart disease.     

Different contributions of endothelin-A and endothelin-B receptors in the pathogenesis of deoxycorticosterone acetate-salt-induced hypertension in rats

We investigated the involvement of actions mediated by endothelin-A (ETA) and endothelin-B (ETB) receptors in the pathogenesis of deoxycorticosterone acetate (DOCA)-salt-induced hypertension in rats. Two weeks after the start of DOCA-salt treatment, rats were given ABT-627 (10 [mg/kg]/d), a selective ETA receptor antagonist; A-192621 (30 [mg/kg]/d), a selective ETB receptor antagonist; or their vehicle for 2 weeks. Uninephrectomized rats without DOCA-salt treatment served as controls. Treatment with DOCA and salt for 2 weeks led to a mild but significant hypertension; in vehicle-treated DOCA-salt rats, systolic blood pressure increased markedly after 3 to 4 weeks. Daily administration of ABT-627 for 2 weeks almost abolished any further increases in blood pressure, whereas A-192621 did not affect the development of DOCA-salt-induced hypertension. When the degree of vascular hypertrophy of the aorta was histochemically evaluated at 4 weeks, there were significant increases in wall thickness, wall area, and wall-to-lumen ratio in vehicle-treated DOCA-salt rats compared with uninephrectomized control rats. The development of vascular hypertrophy was markedly suppressed by ABT-627. In contrast, treatment with A-192621 significantly exaggerated these vascular changes. In vehicle-treated DOCA-salt rats, renal blood flow and creatinine clearance decreased, and urinary excretion of protein, blood urea nitrogen, fractional excretion of sodium, and urinary N-acetyl-beta-glucosaminidase activity increased. Such damage was overcome by treatment with ABT-627 but not with A-192621; indeed, the latter agent led to worsening of the renal dysfunction. Histopathologic examination of the kidney in vehicle-treated DOCA-salt rats revealed tubular dilatation and atrophy as well as thickening of small arteries. Such damage was reduced in animals given ABT-627, whereas more severe histopathologic changes were observed in A-192621-treated animals. These results strongly support the view that ETA receptor-mediated action plays an important role in the pathogenesis of DOCA-salt-induced hypertension. On the other hand, it seems likely that the ETB receptor-mediated action protects against vascular and renal injuries in this model of hypertension. A selective ETA receptor antagonist is likely to be useful for treatment of subjects with mineralocorticoid-dependent hypertension, whereas ETB-selective antagonism alone is detrimental to such cases.     

Synergistic effects of AT(1) and ET(A) receptor blockade in a transgenic, angiotensin II-dependent, rat model

Angiotensin II and endothelin may participate in increasing blood pressure and inducing end-organ damage, but the evidence is conflicting. We tested the hypothesis that endothelin(A) receptor blockade would ameliorate blood pressure and end-organ damage in a rat model of human renin-dependent hypertension. We studied rats that were transgenic for both the human renin and angiotensinogen genes. Experimental groups (n=12 each) of untreated transgenic rats, transgenic rats receiving subdepressor doses of losartan (10 mg/kg), transgenic rats receiving LU 135252 (30 mg/kg), transgenic rats receiving both drugs, and nontransgenic rats were studied between 6 to 10 weeks of age. Blood pressure was measured with tail-cuff sphygmomanometry. Gene expression for atrial natriuretic peptide, collagen III, and ACE was measured. The mortality rate in untreated transgenic rats was 42%, which is consistent with previous observations in this line. Single losartan or LU 135252 treatment reduced mortality incidence to 1 rat per group (8%), without significantly lowering blood pressure. In the combination group, blood pressure was normalized and all rats survived. The drug combination also decreased elevated water intake in transgenic rats to normal levels and significantly reduced cardiac hypertrophy. Furthermore, the combination of drugs decreased cardiac atrial natriuretic peptide, ACE gene, and renal collagen III gene expression. We suggest that endothelin participates in this model of angiotensin II-induced hypertension and end-organ damage. Our findings may have clinical implications and provide a rationale for combining angiotensin II type 1 receptor and endothelin(A) receptor blockade to obtain a synergistic effect.     

Endothelin, vascular hypertrophy, and hypertension

Summary The endothelins (ET-1,2, and 3) constitute a family of 21 amino-acid peptides with potent biological activities. They are synthesized in several tissues, including the vascular endothelium (ET-1 exclusively) and smooth muscle cells. The production and release of endothelin is stimulated by many factors, hormonal and metabolic, and by growth factors, hypoxia, and shear stress. Released endothelin binds to the endothelin receptors ET_A and ET_B, the ET_A receptors on vascular smooth muscle cells mediating vasoconstriction, and the ET_B receptors on the endothelium linked to nitric oxide (NO) and prostacyclin release. The ET_A receptors activate the PLC-IP₃-DAG transduction pathway, which through an increase in cytosolic Ca²⁺ and protein kinase C (PKC) causes vasoconstriction and stimulation of vascular smooth muscle cell growth and proliferation. In the pathogenesis of vascular hypertrophy in hypertension, there is a complex interaction between endothelin, angiotensin II, 795-1 agonists, Ca²⁺, and other growth factors. In animal models of hypertension, endothelin causes vascular hypertrophy, more pronounced in deoxycorticosterone acetate (DOCA)-salt hypertension in the rat than in the spontaneously hypertensive rat. In humans there is an increase in the plasma concentration of endothelin in severe atherosclerotic disease, but not consistently in hypertension. Evidence for the role of endothelin in the vascular hypertrophy of human hypertension is scanty, but the development of nonpeptide and receptor subtype-selective antagonists will permit meaningful studies, including clinical trials of a new class of antihypertensive agents.     

Limitation of infarct size and attenuation of myeloperoxidase activity by an endothelin A receptor antagonist following ischaemia and reperfusion

It has previously been shown that endothelin (ET) receptor antagonists limit myocardial ischaemia/reperfusion (I/R) injury. The mechanism behind this effect is still unclear. The aim of this study was to elucidate the possible relationship between cardioprotection by an ET_A receptor antagonist and inhibition of neutrophil accumulation or activation in the myocardium determined as myeloperoxidase (MPO) activity during I/R. Anaesthetised pigs were subjected to 45 min ischaemia by ligation of the left anterior descending coronary artery (LAD) followed by 4 h of reperfusion. Infiltration of MPO-containing cells, presumably neutrophils, into the ischaemic area was confirmed with an immunohistochemical technique using antibodies against porcine MPO. Vehicle (n = 7) or the selective ETA receptor antagonist LU 135252 (LU; n = 7) were given into the LAD during the last 10 min of ischaemia and the first 5 min of reperfusion. There were no significant differences in LAD flow, mean arterial pressure, heart rate, or rate pressure product between the groups during I/R. The area at risk was similar in the two groups. LU reduced the final infarct size to 40 ± 6 % of the area at risk compared to 80 ± 6 % in the vehicle group (P < 0.001). Endothelin-like immunoreactivity increased 2-fold in the ischaemic area in the vehicle group (P < 0.01), but not in the group given LU. MPO activity was higher (2.5x) in the ischaemic than in the non-ischaemic myocardium of the vehicle group. The MPO activity in the ischaemic myocardium was significantly lower in the group given LU (7.0 ± 1.2 units g⁻¹) than in the vehicle group (14.2 ± 1.9 units g⁻¹; P < 0.01). There was a significant correlation between the infarct size and MPO activity (P < 0.01, r = 0.68). In conclusion, local administration of the selective ET_A receptor antagonist LU during the last period of ischaemia and early reperfusion reduces the extent of myocardial necrosis and MPO activity. This suggests that LU may exert its cardioprotective effect by inhibiting neutrophil-mediated injury. Received: 20 November 2000, Returned for revision: 11 December 2000, Revision received: 9 February 2001, Accepted: 13 February 2001     

Effect of an ET(B)-selective and a mixed ET(A/B) endothelin receptor antagonist on venomotor tone in deoxycorticosterone-salt hypertension

OBJECTIVES: Because the ET(B) receptor is important in venoconstriction, we examined the effects of a selective ET(B) receptor antagonist (A-1 92621) and a mixed ET(A/B) receptor antagonist (A-182086) on endogenous endothelin-1 (ET-1) contributions to elevated venomotor tone in deoxycorticosterone acetate-salt (DOCA-salt) hypertension. METHODS: Changes in venomotor tone were assessed using repeated measurements of mean circulatory filling pressure (MCFP) in awake, uninephrectomized, DOCA-salt-treated rats and uninephrectomized sham rats following intravenous (i.v.) injections of the ET(B) antagonist (12 mg/kg i.v.) or the ET(A/B) antagonist (12 mg/kg i.v.) alone, or 1 h before ganglion blockade with hexamethonium (30 mg/kg i.v.). RESULTS: DOCA-salt rats were hypertensive and exhibited higher MCFP than sham normotensive rats. The ET(A/B) receptor antagonist lowered mean arterial blood pressure (MABP) in DOCA-salt and sham rats, but MCFP fell in DOCA-salt rats only. The ET(B) antagonist produced no changes in MCFP while MABP increased in both groups. Pre-treatment of DOCA-salt rats, but not sham rats, with either antagonist produced greater declines in MCFP following hexamethonium than after hexamethonium alone. CONCLUSIONS: The present study confirms previous findings of elevated MCFP in DOCA-salt hypertensive rats compared to normotensive rats, but is the first to show that venomotor tone is affected by the actions of endogenous ET-1 acting at ET(B) receptors to modulate sympathetic input to the veins, as well as direct actions of ET-1 on vascular smooth muscle (VSM) ET(A) receptors. We also showed that mixed ET(A/B) receptor antagonism was effective in lowering MCFP and MABP in DOCA-salt hypertensive rats.     

Enrasentan,an Antagonist of Endothelin Receptors

Endothelins are powerful vasoconstrictor agents produced by endothelial cells and identified by Yanagisawa et al. in 1988. Two types of receptors for endothelins have been identified: ET_A receptors are located on smooth muscle cells of the vascular wall and are responsible for endothelin‐induced vasoconstriction while ET _B receptors are located on endothelial cells and induce these cells to release NO and prostacyclin. Moreover, these peptides not only cause a potent and prolonged vasoconstriction but are also known to enhance cell proliferation and to stimulate extracellular matrix accumulation. High levels of plasma or tissue endothelins have been found in patients with heart failure, diabetes, stroke, primary pulmonary hypertension, liver cirrhosis and other diseases. Given these effects of endothelins, blocking their receptors might be a new way to reduce blood pressure and to treat other illnesses. Accordingly, many endothelin antagonists have been developed and evaluated in animals and humans. Enrasentan is a mixed ET_A and ET_B receptor antagonist with a higher affinity for ET_A receptors, although it cannot be considered a selective antagonist. In an animal model of hypertension and cardiac hypertrophy the drug has reduced blood pressure, prevented cardiac hypertrophy and preserved myocardial function. In rats with hyperinsulinemia and hypertension enrasentan normalized blood pressure and prevented cardiac and renal damage. In rats with stroke the drug reduced the ischemic area in the brain. Enrasentan has been added to conventional treatment in patients with heart failure (NYHA Class 2‐3) and no addictive effect of the drug has been observed. This is in contrast with results obtained in animal models and still has not been explained. In conclusion, many possible clinical applications can be suggested for this drug, but further studies are necessary to better evaluate its therapeutic efficacy.     

Endothelin receptor function in mesenteric veins from deoxycorticosterone acetate salt-hypertensive rats

OBJECTIVES: To identify the receptors by which endothelin-1 (ET-1) increases venomotor tone in hypertension. METHODS: Vascular reactivity to ET-1 and the selective endothelin receptor subtype B (ET(B)) agonist, sarafotoxin 6c (S6c), was studied in mesenteric blood vessels from deoxycorticosterone acetate (DOCA-salt) hypertensive and normotensive control rats. The diameter of small (< or = 280 microm) mesenteric arteries and veins was monitored in vitro using computer-assisted video microscopy. Contractions of mesenteric arteries (< or= 250 microm diameter) were also studied, using a myograph. ET-1 mRNA levels were measured in mesenteric arteries and veins using real-time RT-PCR techniques. RESULTS : ET-1-induced contractions were reduced in arteries of DOCA-salt hypertensive rats compared with those of normotensive control rats; S6c produced negligible contractions in arteries from both groups. ET-1 concentration-responses curves in arteries measured using video microscopy or a myograph were similar. ET-1 and S6c caused veins to contract, and there were no differences between responses to these agonists in tissues from DOCA-salt hypertensive rats or normotensive control rats. Studies using ET(A) and ET(B) receptor antagonists indicated that ET-1-induced venoconstriction was mediated by ET(A) receptors. Potassium chloride concentration-response curves were similar in arteries and veins from normotensive control rats and DOCA-salt hypertensive rats. ET-1 mRNA levels in DOCA-salt hypertensive rat arteries or veins were not different from those in normotensive control rat arteries and veins. CONCLUSIONS : These data indicate that ET-1 reactivity is maintained in mesenteric veins, but not arteries, in DOCA-salt hypertension. Therefore, the sustained increase in venomotor tone mediated by ET(A) receptors that is known to occur in vivo in DOCA-salt hypertensive rats is not caused by direct venoconstriction.     

Early therapeutic experience with the endothelin antagonist BQ-123 in pulmonary hypertension after congenital heart surgery

OBJECTIVE—To assess the effect of endothelin type A (ET_A) receptor antagonism in infants with pulmonary hypertension following corrective surgery for congenital heart disease.
DESIGN—Open label, preliminary study.
SETTING—Tertiary paediatric cardiothoracic surgical centre.
PATIENTS—Three infants (aged 3 weeks, 7 weeks, and 8 months) with postoperative pulmonary hypertension unresponsive to conventional treatment, including inhaled nitric oxide.
INTERVENTIONS—Patients received incremental intravenous infusions (0.1 to 0.3 mg/kg/h) of the ET_A receptor antagonist BQ-123.
MAIN OUTCOME MEASURES—The response to BQ-123 administration was determined using continuous invasive monitoring of cardiorespiratory variables.
RESULTS—BQ-123 infusion caused a reduction in the ratio of pulmonary to systemic pressures (0.62 (0.01) to 0.52 (0.03), mean (SEM)) with an accompanying decrease in right ventricular stroke work index (4.6 (0.4) to 2.5 (0.3) g/m) and a tendency for the cardiac index to rise (2.1 (0.2) to 2.7 (0.6) l/min/kg/m²). This was associated with a well tolerated fall in the arterial partial pressure of oxygen (16.5 (4.1) to 12.4 (3.3) kPa) and mean systemic arterial pressure (57 (3) to 39 (3) mm Hg).
CONCLUSIONS—ET_A receptor antagonism in infants with postoperative pulmonary hypertension after corrective surgery for congenital heart disease led to significant improvement in pulmonary haemodynamic indices. However, these benefits were associated with reductions in systemic blood pressure and arterial oxygen saturation, the latter consistent with a ventilation-perfusion mismatch. On the basis of these results, studies in pulmonary hypertension will need to proceed with caution.


Keywords: endothelin-1; pulmonary hypertension; receptor antagonism; congenital heart disease     

Improvement of renal dysfunction in rats with chronic heart failure after myocardial infarction by treatment with the endothelin A receptor antagonist, LU 135252

OBJECTIVE: To investigate the role of an activated endothelin system in the renal dysfunction observed in chronic heart failure after myocardial infarction. METHODS: In rats with heart failure after myocardial infarction and in sham-operated animals (Sham), we investigated the effect on renal function of long-term oral treatment with the selective endothelin A (ETA) receptor antagonist, LU 135252 (30 mg/kg per day; groups MI/LU and Sham/LU) or placebo (groups MI/P, Sham/P). Only animals with extensive myocardial infarction (at least 46% of the left ventricle) were included in the study. Infarct size was matched between groups MI/P and MI/LU. Endogenous creatinine clearance, fractional sodium excretion, and plasma and urinary concentrations of endothelin were determined 12 weeks after myocardial infarction. RESULTS: Endogenous creatinine clearance was significantly lower in group MI/P than in group Sham/P (MI/P: 0.64 +/- 0.05, Sham/P: 0.81 +/- 0.04 ml/min per 100 g body weight; P= 0.01 (means +/- SEM)). Treatment with LU 135252 completely prevented the decline in creatinine clearance in rats with chronic myocardial infarction (MI/LU: 0.98 +/- 0.21; Sham/LU: 0.83 +/- 0.10). Fractional sodium and protein excretion did not differ among the four groups. Group MI/P had a marked increase in plasma endothelin concentrations, which was not affected by treatment with LU 135252. Urinary endothelin excretion was significantly lower in group MI/P than in group Sham/P. In the treatment groups, no difference could be observed between animals that had suffered myocardial infarction and the sham-operated group, although LU 135252 markedly increased the urinary excretion of endothelin. CONCLUSION: Our data demonstrate a restoration of impaired renal function in chronic ischaemic heart failure by treatment with the selective ETA receptor antagonist, LU 135252. These results offer a promising therapeutic option for the treatment of renal insufficiency in patients with chronic heart failure.     

Renin–angiotensin system blockade alone or combined with ETA receptor blockade: effects on the course of chronic kidney disease in 5/6 nephrectomized Ren-2 transgenic hypertensive rats

Background: Early addition of endothelin (ET) type A (ET_A) receptor blockade to complex renin–angiotensin system (RAS) blockade has previously been shown to provide better renoprotection against progression of chronic kidney disease (CKD) in Ren-2 transgenic hypertensive rats (TGR) after 5/6 renal ablation (5/6 NX). In this study, we examined if additional protection is provided when ET_A blockade is applied in rats with already developed CKD. Methods: For complex RAS inhibition, an angiotensin-converting enzyme inhibitor along with angiotensin II type 1 receptor blocker was used. Alternatively, ET_A receptor blocker was added to the RAS blockade. The treatments were initiated 6 weeks after 5/6 NX and the follow-up period was 50 weeks. Results: When applied in established CKD, addition of ET_A receptor blockade to the complex RAS blockade brought no further improvement of the survival rate (30% in both groups); surprisingly, aggravated albuminuria (588 ± 47 vs. 245 ± 38 mg/24 h, p < 0.05) did not reduce renal glomerular injury index (1.25 ± 0.29 vs. 1.44 ± 0.26), did not prevent the decrease in creatinine clearance (203 ± 21 vs. 253 ± 17 µl/min/100 g body weight), and did not attenuate cardiac hypertrophy to a greater extent than observed in 5/6 NX TGR treated with complex RAS blockade alone. Conclusions: When applied in the advanced phase of CKD, addition of ET_A receptor blockade to the complex RAS blockade brings no further beneficial renoprotective effects on the CKD progression in 5/6 NX TGR, in addition to those seen with RAS blockade alone.