Nonselective Endothelin Receptor Research Articles

Angiotensin II‐induced increase in myocardial distensibility and its modulation by the endocardial endothelium in the rabbit heart

As recently demonstrated, angiotensin II (Ang II) induces an increase in myocardial distensibility. Although endothelin-1 and the endocardial endothelium (EE) also modulate myocardial diastolic properties, their interaction with Ang II at this level has not yet been investigated. Increasing concentrations of Ang II (from 10(-8) to 10(-5) M) were studied in rabbit right papillary muscles in the following conditions: (1) baseline; (2) after selective removal of EE with Triton X-100; and (3) with intact EE in presence of a non-selective endothelin receptor antagonist (PD-145065), a selective endothelin type A receptor antagonist (BQ-123), an inhibitor of nitric oxide synthesis (N(G)-nitro-L-arginine (L-NA) or an inhibitor of the NAD(P)H oxidase (apocynin). At baseline, Ang II induced a concentration-dependent positive inotropic effect and an increase in passive muscle length (L) up to 1.020 +/- 0.004 L/L(max). After restoring muscle length to maximal physiological length (L(max)), passive tension decreased by 46.1 +/- 4.0%. When the EE was removed, the effect on myocardial distensibility was abolished. With intact EE in presence of PD-145065, BQ-123 or L-NA, the effects of Ang II on myocardial distensibility were attenuated, with a maximal increase in passive muscle length of 1.0087 +/- 0.0012, 1.0068 +/- 0.0022 and 1.0066 +/- 0.0020 L/L(max) and a decrease in resting tension of 22.6 +/- 3.6, 16.1 +/- 6.0 and 20.4 +/- 5.6%, respectively. In the presence of apocynin, the effect on myocardial distensibility was abolished. In conclusion, the Ang II-dependent acute increase in myocardial distensibility is abolished by the selective removal of the EE and attenuated in the presence of endothelin-1 receptor antagonists, an inhibitor of nitric oxide synthesis or an inhibitor of NAD(P)H oxidase.

Inhomogeneous vasomotor effects of moderate selective and non-selective endothelin-receptor blockade in stable coronary artery disease

Objective:To explore the morphological and functional effect of selective and non-selective endothelin (ET)-receptor blockade in coronary artery disease (CAD).Design:Prospective randomised controlled trial.Setting:University hospital.Patients:26 patients with stable CAD.Interventions:Intracoronary infusion (30 minutes)...

Endothelin receptor antagonists in preclinical models of pulmonary hypertension

Pulmonary hypertension (PH), a chronic disorder of the pulmonary vasculature, is characterized by progressive elevation in pulmonary artery pressure and the ultimate development of right-sided heart failure and death. Being a rapidly progressive disease with limited therapeutic options, the pathogenesis of PH is complex and multifactorial. The pathogenesis may result from a combination of vasoconstriction, inward vascular wall remodelling and in situ thrombosis that involves dysfunction of underlying cellular pathways and mediators. Among these, the activation of endothelin (ET) system has been shown to be important in the development and perpetuation of PH. Endothelin-1 (ET-1), a potent vasoconstrictor and mitogen, exerts its biological effects by binding to two G-protein-coupled receptor isoforms, endothelin A (ETA) receptor and endothelin B (ETB) receptor. These two receptors are nonredundant and unique because of distinct localization, unique binding locations and affinities for the endothelin peptide and activation of distinct signalling pathways. Importantly, there is now substantial evidence that direct antagonism of ET receptors that can block either ETA- or ETA- and ETB receptors can be beneficial for the treatment of PH in both preclinical and clinical setting. This review provides an overview of endothelin biology, various preclinical models that have been widely used to investigate the pathophysiology of PH as well as the individual roles of the ET receptors (ETA and ETB) and their regulation in disease pathogenesis. We also review current data on the use of selective and nonselective ET receptor antagonism in the preclinical PH models.

Potential Role of Endothelin in Patients with Acute Pulmonary Embolism and Chronic Thromboembolic Pulmonary Hypertension

Endothelins (ET), a family of three peptides of strong vasoconstrictive properties, participate in the regulation of vascular tone and blood flow. The synthesis and degradation of the ET predominantly take place in the pulmonary vasculature. Elevated plasma ET levels were reported in various forms of arterial pulmonary hypertension including chronic thromboembolic pulmonary hypertension (CTEPH). Moreover, clinical studies with nonselective ET receptor antagonist - bosentan reported improvement in functional class in patients with CTEPH. It has been suggested that endothelins may play an important role in acute pulmonary thromboembolism (APE). However, further studies are necessary to verify these observations. In the current paper we discuss a potential role of endothelins in CTEPH and APE.

Successful switch to sitaxsentan in a patient with HIV-related pulmonary arterial hypertension and late intolerance to nonselective endothelin receptor blockade

Pulmonary arterial hypertension [PAH] is a rare but well-known cardiovascular condition potentially associated with human immunodeficiency virus [HIV] infection and is currently recognized to be one of the most ominous noninfectious HIV complications. Although there is no clear evidence supporting the use of any medication for the treatment of HIV-related PAH, many of the currently available agents have been shown to exert some clinical benefits HIV-PAH patients. To date, no data are available regarding the potential effects of sitaxsentan, a selective endothelin type-A receptor antagonist, in this peculiar patient population. We report the case of a successful switch to sitaxsentan in a HIV-infected patient with PAH initially receiving bosentan who developed a late treatment-related side-effect.

Abstract 1499: Angiotensin And Endothelin Systems - Important Players In Urotensin II Induced Myocardial Distensibility

Objective: Urotensin II (U-II) is a vasoactive peptide with important actions in the cardiovascular system. It was recently shown that it acutely decreases myocardial stiffness. Although angiotensin II (AngII) and endothelin-1 (ET-1) also modulate myocardial diastolic properties, their interaction with U-II at this level has not yet been investigated. Methods: Effects of increasing concentrations of U-II (10 – 8–10 – 6M) were studied in rabbit papillary muscles immersed in a modified Krebs solution (0.6Hz;1.8mM Ca2+;35°C) in the absence (n=12) and in presence of losartan, a selective competitive antagonist of AngII receptor type 1 (10 – 6M;n=8) or PD-145065, a nonselective endothelin receptor antagonist (10 – 6M;n=6). Calculated parameters: passive tension (PT), active tension (AT), maximum velocity of tension rise and decline (dT/dtmax and dT/dtmin, respectively) and muscle length. Results presented as mean±SEM (p<0.05). Results: U-II induced a concentration dependent negative inotropic and lusitropic effects, decreasing at 10 – 6M 15.8±5.6%AT, 13.5±5.4%dT/dtmax and 18.1±4.5%%dT/dtmin. This effect was inhibited by losartan or PD-145065. Additionally, U-II induced a concentration dependent increase in passive muscle length of 1.0081±0.002L/ Lmax. Restoring muscle length to Lmax decreased 19.5±3.5%PT, indicating increased myocardial distensibility. In the presence of PD-145065, the maximal concentration of U-II only increased muscle length to 1.004±0.002%L/Lmax, which corresponded to a decrease of PT of just 11.6±2.7%. With losartan these effects of U-II were abolished. Conclusion: The acute increase in myocardial distensibility induced by U-II is attenuated by ET-1 receptor blockade and completely abolished in the presence of an AT1 antagonist. This interaction between U-II, AngII and ET-1 is a novel finding with potential pathophysiologic and therapeutic implications in heart failure that deserves further investigation.

Medikamentöse Therapie des Lungenhochdrucks bei Patienten mit angeborenen Herzfehlern

The development of drugs for lowering pressures in pulmonary arterial hypertension (PHT) has provided possible therapeutic application in patients with pulmonary hypertension associated with congenital heart disease (CHD). Prostanoids, both nonselective and selective endothelin-receptor antagonists and phosphodiesterase-V inhibitors have been used for this purpose. The efficacy of these drugs - from different classes of bioactivity - in this context have been shown in several studies. However, the long-term effects of drug treatment on prognosis and course of PHT have not yet been adequately investigated. The current status of drug treatment of PHT in patients with CHD is reviewed in this article.

Evaluation of bosentan for idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a quality-of-life-altering and life-shortening lung disease manifested by physiologic restriction, hypoxemia and progressive shortness of breath. Despite nearly 30 years of investigation, the median survival for patients with this disease remains dismal at approximately 3 years from the time of diagnosis. Recent investigations have identified a number of potential molecular therapeutic targets for IPF that include endothelin-1 and other fibrogenic cytokines. Bosentan, a nonselective endothelin receptor antagonist approved in the USA and Europe for the treatment of patients with pulmonary arterial hypertension, is currently undergoing evaluation as a potential therapy for IPF. A recently completed multinational, placebo-controlled trial failed to show a beneficial impact of bosentan on the primary end point, but results from a hypothesis-generating, post hoc analysis of data from this trial have prompted an assessment of the drug for efficacy in a selected subgroup of IPF patients – those with biopsy-proven IPF and little radiographic honeycombing. Results from this trial are anticipated in 2009.

Endothelin receptor antagonists in pulmonary arterial hypertension

The endothelin (ET) system, especially ET-1 and the ET(A) and ET(B) receptors, has been implicated in the pathogenesis of pulmonary arterial hypertension (PAH). Together with prostanoids and phosphodiesterase 5 inhibitors, ET receptor antagonists have become mainstays in the current treatment of PAH. Three substances are currently available for the treatment of PAH. One of these substances, bosentan, blocks both ET(A) and ET(B) receptors, whereas the two other compounds, sitaxsentan and ambrisentan, are more selective blockers of the ET(A) receptor. There is ongoing debate as to whether selective or nonselective ET receptor blockade is advantageous in the setting of PAH, although there is no clear evidence that receptor selectivity is relevant with regard to the clinical effects of these drugs. For the time being, other features, such as safety profiles and the potential for pharmacokinetic interactions with other drugs used in the treatment of PAH, may be more important than selectivity or nonselectivity when selecting treatments for individual patients.

Effects of nonselective endothelin-1 receptor antagonism on cardiac mast cell-mediated ventricular remodeling in rats

The objective of this study was to investigate the effect a nonselective endothelin-1 (ET-1) receptor antagonist (bosentan) had on the acute myocardial remodeling process including left ventricular (LV) mast cells and matrix metalloproteinase (MMP) activity secondary to volume overload. Additionally, we investigated the overall functional outcome of preventative endothelin receptor antagonism during 14 days of chronic volume overload. LV tissue from sham-operated (Sham), untreated-fistula (Fist), and bosentan (100 mg.kg(-1).day(-1))-treated animals (Fist + Bos) was analyzed for mast cell density, MMP activity, and myocardial collagen volume fraction at 1 and 5 days after the creation of an aortocaval fistula. When compared with untreated fistulas, bosentan treatment prevented the marked increase in LV mast cell density at 1 day postfistula (3.1 +/- 0.3 vs. 1.3 +/- 0.3 LV mast cells/mm2, Fist vs. Fist + Bos, P <or= 0.01). Additionally, the substantial increase in MMP-2 activation in the untreated fistula at 1 day was prevented following bosentan treatment (1.6 +/- 0.3 vs. 0.9 +/- 0.1 arbitrary activity units, Fist vs. Fist + Bos, P <or= 0.01). The marked decrease in collagen volume fraction seen in the Fist group (1.4 +/- 0.1 vs. 0.8 +/- 0.1% myocardial tissue, Sham vs. Fist, P <or= 0.01) was significantly attenuated following bosentan treatment at both the 1- and 5-day time points. Lastly, a 2-wk preventative treatment with bosentan resulted in significant attenuation of the increase in LV end-systolic and -diastolic volumes compared with those in untreated fistula hearts. In summary, nonselective ET-1 antagonism prevents the acute increases in cardiac mast cell density and MMP activation induced secondary to chronic volume overload. By preventing these events, ET-1 antagonism was efficacious in attenuating ventricular dilatation and limiting the development of structural and functional deficits in the first 2 wk of chronic volume overload. Accordingly, these results are the first to demonstrate that cardiac mast cells are responsive to the endogenous endothelin system in vivo. Another novel finding from this study is that chronic nonspecific endothelin antagonism may inadvertently potentiate ET-1-mediated signaling.

Lack of renal improvement with nonselective endothelin antagonism with tezosentan in type 2 hepatorenal syndrome

Renal vasoconstriction is a key factor in the development of hepatorenal syndrome (HRS) and may be secondary to increased activities of endothelin-1, a potent renal vasoconstrictor. To assess the effects of tezosentan, a nonselective endothelin receptor antagonist, on renal function in patients with type 2 HRS, six male patients, 56.3 +/- 2.5 years old, with cirrhosis and type 2 HRS were treated with tezosentan; ascending doses of 0.3, 1.0, and 3.0 mg/hour, each for 24 hours, were used for the initial 2 patients, but a constant dose of 0.3 mg/hour for up to 7 days was used for the remaining 4 patients. The glomerular filtration rate, renal plasma flow, 24-hour urinary volume, mean arterial pressure (MAP), heart rate, tezosentan levels, and vasoactive hormones were measured daily. Albumin was given as required. The study was stopped early because of concerns about the safety of tezosentan in type 2 HRS. Five patients discontinued the study early; one stopped within 4 hours because of systemic hypotension (MAP < 70 mm Hg), and 4 patients stopped at approximately 4 days because of concerns about worsening renal function (serum creatinine increased from 180 +/- 21 to 222 +/- 58 micromol/L, P > 0.05) and decreasing urine volume (P = 0.03) but without a significant change in MAP. The plasma tezosentan concentrations were 79 +/- 34 ng/mL at a steady state during infusion at 0.3 mg/hour. The plasma endothelin-1 concentrations increased from 2.7 +/- 0.3 pg/mL at the baseline to 19.1 +/- 7.3 pg/mL (P < 0.05). An endothelin receptor blockade potentially can cause a deterioration in renal function in patients with cirrhosis and type 2 HRS. Caution should be taken in future studies using endothelin receptor antagonists in these patients.

Interactive modulation of renal myogenic autoregulation by nitric oxide and endothelin acting through ET-B receptors

In rats, nitric oxide modulates renal autoregulation in steady-state experiments and the myogenic mechanism in dynamic studies. Interactive modulation of autoregulation by nitric oxide and endothelin-1, predominantly involving endothelin B receptors, has been reported although it remains unclear whether the interaction is synergistic or obligatory or whether it affects the myogenic component of autoregulation. Nonselective inhibition of nitric oxide synthase (L(omega)-nitro-l-arginine methyl-ester; l-NAME) with endothelin A and B selective receptor antagonists BQ-123 and BQ-788, all infused into the renal artery, plus time series analysis were used to test the interactive actions of nitric oxide and endothelin on renal vascular conductance and on autoregulation. Nonselective endothelin receptor antagonism blunted the constrictor response to subsequent l-NAME but had no effect on previously established l-NAME-induced vasoconstriction. BQ-123 did not affect conductance and caused only minor reduction in myogenic autoregulatory efficiency. Responses to BQ-123 and l-NAME were additive and not interactive. BQ-788 and l-NAME each caused strong vasoconstriction alone and in the presence of the other, indicating that coupling between nitric oxide- and endothelin B-mediated events is not obligatory. l-NAME augmented myogenic autoregulation, and subsequent BQ-788 did not alter this response. However, BQ-788 infused alone also enhanced myogenic autoregulation but resulted in significant impairment of myogenic autoregulation by subsequent l-NAME. Thus the interaction between nitric oxide and endothelin is clearly nonadditive and, because it is asymmetrical, cannot be explained simply by convergence on a common signal pathway. Instead one must postulate some degree of hierarchical organization and that nitric oxide acts downstream to endothelin B activation.

Endothelin receptors, localized in sympathetic nerve terminals of the heart, modulate norepinephrine release and reperfusion arrhythmias

Endothelin (ET)-1 is an endogenous vasoconstrictor which modulates norepinephrine (NE) release in myocardial ischemia reperfusion. Recent studies have demonstrated the pro- or anti-arrhythmic effects in reperfusion. The present studies were undertaken to test the hypothesis that ET receptors located in sympathetic nerve terminals modulate NE release associated with reperfusion arrhythmias (ventricular fibrillation; VF). Immunohistochemical studies showed that both ETA and ETB receptors exist in the sympathetic nerve varicosities, which were stained positive for tyrosine hydroxylase (TH) in the left ventricular wall in guinea pigs. Isolated guinea pig hearts were subjected to 20 min of normothermic global ischemia followed by 30 min reperfusion. Exogenously applied ET-1 (0.1 and 1 nM) dose-dependently increased NE release and the duration of VF, but these responses were significantly suppressed with the Na(+)/H(+) exchanger inhibitor, 5-(N-ethyl-N-isopropyl)-amiloride (10 microM). The ETA receptor antagonist (BQ123, 1 microM) and nonselective ET receptor antagonist (PD142893, 1 microM) significantly attenuated NE release and VF, whereas the ETB receptor antagonist (BQ788,300 nM) markedly elevated NE release but did not affect VF. These studies provide the first evidence that both ETA and ETB receptors, located in the sympathetic nerve varicosities, modulate NE release, at least in part, in association with reperfusion arrhythmias.

Role of endothelin and endothelin receptor antagonists in renal disease

Endothelin (ET)-1 is a potent vasoconstrictor peptide with pro-inflammatory, mitogenic, and pro-fibrotic properties that is closely involved in both normal renal physiology and pathology. ET-1 exerts a wide variety of biological effects, including constriction of cortical and medullary vessels, mesangial cell contraction, stimulation of extracellular matrix production, and inhibition of sodium and water reabsorption along the collecting duct, effects that are primarily mediated in an autocrine/paracrine manner. Increasing evidence indicates that the ET system is involved in an array of renal disorders. These comprise chronic proteinuric states associated with progressive glomerular and tubulointerstitial fibrosis, including diabetic and hypertensive nephropathy, glomerulonephritis and others. In addition, ET-1 is causally linked to renal disorders characterized by increased renal vascular resistance, including acute ischaemic renal failure, calcineurin inhibitor toxicity, endotoxaemia, hepatorenal syndrome and others. Furthermore, derangement of the ET system may be involved in conditions associated with inappropriate sodium and water retention; for example, in congestive heart failure and hepatic cirrhosis. Both selective and non-selective ET receptor antagonist have been developed and tested in animal models with promising results. As key events in progressive renal injury like inflammation and fibrosis are mediated via both ET(A) and ET(B) receptors, while constrictor effects are primarily transduced by ET(A) receptors, dual ET receptor blockade may be superior over selective ET(A) antagonism. Several compounds have been developed with remarkable effects in several models of acute and progressive renal injury. Thus, clinical studies are required to assess whether these results can be confirmed in humans, hopefully leading to novel and effective therapeutic options with few side effects.

Effect of endothelin-1 on erythropoietin production in a rat model under normoxia and functional carbon monoxide-induced hypoxia

It has been hypothesized that autacoids, such as endothelin-1 (ET), may modulate erythropoietin (Epo) secretion. Therefore, we studied the effect of ET-1 infusion and of a nonselective ET(A/B) receptor antagonist on Epo secretion under carbon monoxide (CO) exposure. Anesthetized rats were supplied with room temperature air containing increasing concentrations of CO by an aerating cap. A CO-Epo dose-response curve over the range of 0.02-0.14 vol% CO was conducted. Subpressor doses of ET-1 (3 pmol/min/kg BW) and the ET(A/B) receptor antagonist LU302872 (LU; 30 mg/kg) were applied to anaesthetized rats under normoxia (controls CON, ET, LU) and following hypoxia (CO exposure; H-CON, H-ET, H-LU). Mean arterial blood pressure (MAP), glomerular filtration rate (GFR, inulin clearance), Epo and ET-1 serum concentrations (ELISA) and renal Epo mRNA (Light Cycler) were determined. The EC50 value for CO was 0.1 vol% with a 70-fold increase in Epo serum concentrations. CO exposure increased Epo serum and Epo mRNA concentrations in the expected range in all groups. None of the treatments with ET or LU influenced the effect of hypoxia on Epo serum concentrations and renal Epo mRNA content. Under hypoxia, administration of ET-1 as well as LU prevented the hypoxia-induced decrease in MAP (p<0.05). Under hypoxia, GFR was reduced by 50% except for H-LU with values comparable to normoxia. Taken together, the influence of hypoxia exceeds by far the effect of ET-1 on Epo production, irrespective of the presence or absence of exogenous ET-1. Thus, ET-1 does not appear to be a major modulator of Epo production.

Contribution of endothelin-1 to the enhanced carotid body chemosensory responses induced by chronic intermittent hypoxia

Chronic intermittent hypoxia (CIH) enhances carotid body (CB) chemosensory responses to acute hypoxia. We tested the hypothesis that endothelin-1 (ET-1), an excitatory modulator of CB chemoreception may contribute to the enhanced CB chemosensory responses in cats exposed to cyclic hypoxic episodes repeated during 8 h for 4 days. Accordingly, we measured the ET-1 immunoreactivity (ET-ir) in the CB and plasma. Using a perfused CB preparation, we studied the effects of exogenous ET-1 and bosentan, a non-selective endothelin receptor type A and B antagonist, on the frequency of chemosensory discharges ( ƒ x ) during normoxia, mild and severe hypoxia. We found that CIH increased ET-ir in the CB by ∼10-fold leaving ET-1 plasma levels unchanged. Application of ET-1 to control and CIH-treated CBs produced long-lasting dose-dependent increases in ƒ x , although the dose–response curve showed a rightward-shift in the CIH-treated CBs. CIH increased baseline ƒ x and hypoxic chemosensory responses, which were reduced by 50 μM bosentan in CBs from CIH-treated cats. Present results suggest that a local increase of ET-1 in the CB may contribute to the enhanced chemosensory responses induced by CIH predominantly through a vasomotor mechanism.

Contrast-induced nephropathy: Pharmacological prophylaxis

Contrast media-associated acute renal failure represents the third most common cause of in-hospital renal function deterioration after decreased renal perfusion and post-operative renal insufficiency. Although generally benign, this complication is associated with a mortality rate ranging from 3.8 to 64%, depending on the increase of creatinine concentration. Multiple drugs have been tested in an attempt to prevent this complication. Central to the pathophysiology of contrast-induced nephrotoxicity (CIN) is an alteration in renal hemodynamics. In an effort to reverse these hemodynamic changes, vasodilators and diuretics have been tested as prophylactic drugs. However, their effectiveness has not been confirmed. Recently, considerable interest has resulted from the initial positive data on the effectiveness of prophylactic administration of antioxidant compounds, such as acetylcysteine and ascorbic acid. In this review, we focus on the effectiveness of pharmacologic therapies for preventing CIN.

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.

Carbon monoxide, but not endothelin-1, plays a major role for the hepatic microcirculation in a murine model of early systemic inflammation

Endothelin-1 and carbon monoxide play a major role in the regulation of liver microcirculation in numerous disease states. During sepsis and endotoxemia, elevated formation of endothelin-1 results in reduced sinusoidal blood flow. However, the role of carbon monoxide and endothelin-1 and its receptors endothelin receptor A and endothelin receptor B in the deranged liver microcirculation during early systemic inflammation remains unclear. Prospective, randomized, controlled experiment. University animal laboratory. Male C57/BL6 mice, weighing 23-27 g. To induce a systemic inflammation, mice were treated with 1 hr of bilateral hind limb ischemia followed by 3 hrs or 6 hrs of reperfusion. Animals were randomly exposed to the nonselective endothelin receptor antagonist Ro-61-6612 (Tezosentan) and/or a continuous endothelin-1 infusion. Different animals were randomized to methylene chloride gavage or carbon monoxide inhalation during the reperfusion period. After ischemia/reperfusion, endothelin-1 plasma concentrations, endothelin-1 messenger RNA expression, and endothelin receptor A and B messenger RNA expression revealed no significant changes when compared with sham animals. After 6 hrs of ischemia/reperfusion, hepatic microcirculatory variables (sinusoidal density, sinusoidal diameter, and red blood cell velocity) deteriorated. Tezosentan after 6 hrs of ischemia/reperfusion did not improve the liver microcirculation, whereas the continuous infusion of endothelin-1 after 6 hrs of ischemia/reperfusion further impaired sinusoidal blood flow. Tezosentan treatment did not produce any alterations in hepatocellular injury or hepatic redox status when compared with the untreated animals receiving 6 hrs of ischemia/reperfusion. Animals receiving 6 hrs of ischemia/reperfusion and exposed to methylene chloride gavage or inhaled carbon monoxide during limb reperfusion showed significantly improved microcirculatory variables, hepatic redox status, and attenuated hepatocellular injury. These data suggest that endothelin-1 and the endothelin receptors A and B are not responsible for the observed hepatic microcirculatory and cellular dysfunction during early systemic inflammation, but exposure to exogenous carbon monoxide protected the hepatic microcirculation and improved the impaired hepatic cellular integrity and the hepatocellular redox status.

Bosentan, an endothelin receptor antagonist, reduces leucocyte adhesion and inflammation in a murine model of inflammatory bowel disease

Endothelins, a group of polyfunctional cytokines, induce the adhesion of circulating leucocytes to venous endothelium, an initial step in the pathogenesis of a cellular infiltrate in inflammatory bowel disease (IBD). The effect of bosentan, a non-selective endothelin receptor antagonist, on leucocyte adhesion and inflammation in a murine model of IBD was studied. Thirty BALB/c mice were divided into three groups of 10 animals: untreated controls, chronic colitis [dextran sodium sulphate (DSS), 3% w/v for 30 days], and treatment with bosentan (30 mg/kg i.p. daily on days 26-30). On day 30, adherent and rolling leucocytes and the average rolling velocity were assessed by intravital microscopy. Clinical and histological activity of inflammation were assessed by the disease activity index and modified Dieleman score, respectively. Kruskal-Wallis test was used, followed by Dunn's method. A value of p<0.05 was considered significant. Compared to healthy controls, mice treated with DSS showed pronounced clinical and histological inflammation, and a higher number of rolling and adhering leucocytes in colonic submucosal venules. Therapy with bosentan significantly reduced clinical and histological inflammation. Adherent leucocyte levels were markedly lower (1.2+/-0.3 vs 23.7+/-2.8 adherent cells per 0.01 mm2, p<0.05). The number of rolling leucocytes was lower but not significantly different. However, rolling velocity was significantly higher (91.5+/-14.0 vs 19.0+/-1.6 microm/s, p<0.05). Bosentan reduces the adhesion of leucocytes in colonic submucosal venules and reduces inflammation in this mouse model of IBD. By inhibiting leucocyte adhesion, a crucial step in the recruitment of leucocytes to the inflamed tissue, bosentan is a potent therapeutic drug in this animal model. Further studies are necessary to investigate the role of bosentan as a novel drug in human IBD.