Endothelin-1 is produced and secreted by neonatal rat cardiac myocytes in vitro

The cardiac endothelium: cardioactive mediators

Endothelial cells within the heart release a number of substances that modulate myocardial contractile function. These agents include nitric oxide, endothelin, prostanoids, adenylpurines, and other substances that have so far been characterized only in bioassay studies. A notable feature of many of these agents is that they influence contractile behavior predominantly by modifying cardiac myofilament properties rather than altering cytosolic Ca2+ transients. A consequence of this subcellular action is often a disproportionate effect on myocardial relaxation and diastolic tone. The paracrine modulation of cardiac myocyte function by endothelial cell factors is likely to be an important mechanism contributing to the overall regulation of cardiac contractile function, both physiologically and in pathological states.

Endothelin antagonism in end-organ damage of spontaneously hypertensive rats. Comparison with angiotensin-converting enzyme inhibition and calcium antagonism

High blood pressure results in cardiac hypertrophy and fibrosis, increased thickness and stiffness of large artery walls, and decreased renal function. The objective of our study was to assess the role of endothelin, angiotensin II, and high blood pressure in the end-organ damage observed in spontaneously hypertensive rats (SHR). For this purpose, SHR were treated for 10 weeks with either a mixed endothelin-A and endothelin-B receptor antagonist, bosentan (100 mg/kg per day), an angiotensin-converting enzyme inhibitor, enalapril (10 mg/kg per day), or a long-acting calcium antagonist, mibefradil (20 mg/kg per day). A group of SHR was left untreated, and a group of normotensive Wistar rats was used as control. At the end of treatment, maximal coronary blood flow was measured in isolated perfused hearts. Cardiac hypertrophy and fibrosis, aortic medial thickness, and extracellular matrix content were evaluated by quantitative morphometry. Proteinuria and urea and creatinine clearances were measured, and renal histopathology was assessed. SHR exhibited cardiac hypertrophy, perivascular fibrosis, and decreased maximal coronary blood flow. Aortic medial thickness was increased, whereas elastin density was decreased. Finally, SHR showed decreased urinary excretion and decreased urea and creatinine clearances. No renal histological lesions were observed. Although bosentan did not affect blood pressure, it normalized renal function and slightly decreased left ventricular hypertrophy and fibrosis. Enalapril and mibefradil were both effective in significantly decreasing blood pressure, left ventricular hypertrophy, and aortic medial thickness and improving coronary blood flow, but in contrast to bosentan, they did not improve creatinine clearance. We conclude that in SHR, high blood pressure plays a major role in end-organ damage and that endothelin may partly mediate renal dysfunction and cardiac remodeling independently of a direct hemodynamic effect.

Is the heart a source for elevated circulating endothelin levels during aorta-coronary artery bypass grafting surgery in human beings?

Reports have shown increased systemic levels of endothelins during coronary artery bypass grafting in human beings. It was not known whether increased endothelin levels during coronary artery bypass grafting reflect a general systemic response to the surgical procedure or increased myocardial production of endothelins in response to ischemia and reperfusion. We therefore measured endothelin levels in the right atrium and proximal aorta of 15 patients undergoing coronary artery bypass grafting for anginal syndrome immediately before aortic crossclamping and again after cessation of cardiopulmonary bypass. In five patients, we also measured coronary sinus levels of endothelins during cardiopulmonary bypass circulation. We found that endothelin levels were elevated throughout the surgical procedure. Right atrial endothelin levels were significantly elevated after cessation of cardiopulmonary bypass circulation with respect to values immediately before aortic crossclamping (11.1 +/- 3.1 vs 14.2 +/- 3.7 pg/ml, p = 0.008), whereas endothelin levels in the proximal aorta did not rise significantly (10.5 +/- 2.3 vs 11.6 +/- 2.4 pg/ml, p > 0.5). Coronary sinus endothelin levels tended to decline temporarily during cardiopulmonary bypass circulation (11.1 +/- 2.1 pg/ml before aortic crossclamping, 7.9 +/- 1.9 1 minute after release of aortic crossclamp, and 9.9 +/- 2.1 pg/ml after release of partial aortic crossclamping, p = 0.06). We conclude that the rise in right atrial endothelin levels during coronary artery bypass grafting reflects systemic production and secretion of endothelins, probably by vasculature or organs distal to the proximal aorta, and is not the result of increased myocardial production and secretion of endothelins.

Effects of the endothelin ETA-receptor antagonist FR139317 on development of hypertension and cardiovascular hypertrophy in deoxycorticosterone acetate-salt hypertensive rats

We investigated the role of endothelin-1 (ET-1) in the development of hypertension and cardiovascular hypertrophy in deoxycorticosterone acetate (DOCA)-salt hypertensive rats. Two weeks after the start of DOCA-salt treatment, the rats were divided into two groups and were given FR139317 [(R)2-[(R)-2-[(S)-2-[[1-(hexahydro-1H-azepinyl)]- carbonyl]amino-4-methyl-pentanoyl]amino-3-[3-(1-methyl-1H-indolyl)] propionyl]amino-3-(2-pyridyl) propionic acid], a specific ETA-receptor antagonist, or its vehicle for 2 weeks. Uninephrectomized rats without DOCA-salt treatment served as controls. Vehicle-treated DOCA-salt rats developed marked hypertension after 4 weeks. FR139317 significantly suppressed the increase in systolic blood pressure with values averaging 163 +/- 8 mmHg (P < 0.05 vs DOCA-salt rats receiving vehicle, 195 +/- 9 mmHg). Morphological studies in the rats given the vehicle showed vascular medial hypertrophy, with a significant increase in the wall area and wall-to-lumen ratio. A marked decrease in vascular wall hypertrophy was observed in the FR139317-treated DOCA-salt rats. The cardiac hypertrophy in DOCA-salt hypertensive rats was also significantly reduced by FR139317. Therefore, these results suggest that ET-1 plays an important role in the development of DOCA-salt hypertension presumably by stimulating the ETA receptor. In addition, we found that an ETA-receptor antagonist effectively reduced cardiovascular hypertrophy in the rats, so the cardiovascular hypertrophy noted in DOCA-salt hypertensive rats may be related to ET-1.

Elevation of endothelin biosynthesis in human endothelial cells with mycoplasma infection

The effects of mycoplasma infection on the biosynthesis of endothelin-1 (ET-1) in cultured human vascular endothelial cell lines were examined to understand regulatory mechanisms of ET-1 biosynthesis and causes of angiopathy due to mycoplasma infection. The growth of normal endothelial cells from the umbilical cord vein and of an immortal endothelial cell line transfected with prepro ET-1 cDNA was decreased, while the secretion of ET-1 into the culture medium was enhanced by mycoplasma infection. However, the rate of ET-1 production in these cell cultures was much higher at the growing phase than at the stationary phase. Immunocytochemical studies with anti-ET-1 antibody and an autoradiographic examination of the labeled nuclei with 3H-TdR revealed that mycoplasma infection induced an elevation of ET-1 production in both S and non-S phase cells. The expression of prepro ET-1 mRNA as examined by in situ hybridization and by RNase protection assay was not altered by mycoplasma infection. Thus, the biosynthesis of ET-1 in vascular endothelial cells may be regulated at the posttranscriptional level.

Cardiac endothelin-1 content and receptor subtype in spontaneously hypertensive rats

Endothelin-1 (ET-1), a newly discovered peptide with potent vasoconstrictor and growth-promoting effects, has been implicated in high blood pressure and cardiac hypertrophy in the spontaneously hypertensive rat (SHR). In the present study, we measured plasma ET-1 levels and tissue ET-1 concentrations in the four cardiac chambers of 17- to 18-week-old SHR and their normotensive controls. Wistar Kyoto (WKY) rats. SHR had slightly but significantly higher plasma ET-1 levels than WKY. The ventricles had the highest ET-1 content and the atria in both strains had the highest ET-1 concentrations. ET receptor subtypes were analysed by radiogand binding with ET-1, BQ-123 and IRL 1620 in crude membrane preparations of the four cardiac chambers. No differences in receptor subtype densities or affinities were apparent between the two strains. ET(A) represented 75 to 85% of both ET receptors. Competition analysis revealed that in both strains left ventricular tissue had lower receptor densities and higher affinities than the atria. These results suggest that ET-1 and its receptor although contributing in the maintenance of high blood pressure may not be an important factor during stable cardiac hypertrophy in adult SHR. The differential distribution of ET-1 content and receptor densities favoring the atria in both strains suggest that this peptide may have a different physiological role in the atria from that in the ventricles.

Increased endothelin-1 gene expression in the endothelium of coronary arteries and endocardium in the DOCA-salt hypertensive rat

Endothelin-1 (ET-1) is a potent vasoconstrictor and inotropic agent which may also induce cell hypertrophy. The role of ET-1 in ventricular hypertrophy in hypertension is unknown. We investigated ET-1 gene expression and immunoreactive ET-1 (ir-ET-1) concentration in the heart of deoxycorticosterone acetate (DOCA)-salt hypertensive rats. To identify the cellular sites of ET-1 production in the heart, we performed in situ hybridization histochemistry. DOCA-treated rats which underwent unilateral nephrectomy (Uni-Nx) or not, exhibited mild systolic blood pressure elevation and ventricular hypertrophy. Blood pressure elevation and cardiac hypertrophy were more severe in DOCA-salt hypertensive rats. Ventricular ET-1 mRNA was similar in Uni-Nx control and DOCA-treated rats by Northern blot analysis, whereas in DOCA-salt hypertensive rats it was significantly increased. Ir-ET-1 concentration was also enhanced in ventricles from DOCA-salt hypertensive rats compared with Uni-Nx control rats. In situ hybridization histochemistry using a 35S-labelled complementary RNA ET-1 probe demonstrated that the level of ET-1 mRNA transcripts was increased exclusively in endothelial cells of large epicardial and small intramyocardial coronary arteries and in areas of the endocardium, but not significantly in myocardial cells of either the atria or ventricles. Enhanced ET-1 production may contribute to vascular changes, both structural and functional, in the heart in this model of hypertension in the rat, but probably does not contribute to the severe cardiac hypertrophy found in DOCA-salt hypertensive rats.

Increased in vivo expression and production of endothelin-1 by porcine cardiomyocytes subjected to ischemia

Circulating levels of the endothelium-derived vasoconstrictor peptide endothelin-1 (ET-1) are increased in association with myocardial ischemia and infarction. The present study investigates whether ET-1 is synthesized and produced locally in the ischemic heart. Sixteen pigs were divided into three groups. In the first group, the left anterior descending coronary artery was occluded for 90 minutes, followed by 150 minutes of reperfusion (group A, n = 8). Two additional groups were subjected to 90 minutes (group B, n = 4) or 240 minutes (group C, n = 4) of ischemia without reperfusion. Biopsies from the nonischemic and ischemic myocardium were rapidly obtained from the beating heart and subsequently examined by Northern blot, in situ hybridization, and immunohistochemistry. Arterial plasma ET-1 was measured before ischemia and at the end of the experiments. Northern blot revealed a twofold increase in ET-1 mRNA in the ischemic myocardium compared with the nonischemic myocardium. In situ hybridization showed a considerable increase in ET-1 mRNA over the ischemic cardiomyocytes. Substantial ET-1-like immunoreactivity (ET-1-ir) was detected in cardiomyocytes in the ischemic region. In contrast, little or no ET-1-ir or mRNA was detected in nonischemic cardiomyocytes. Both in the ischemic and nonischemic regions, little ET-1-ir was detected in vascular endothelial cells or vascular smooth muscle cells. There was no difference in the intensity and distribution of ET-1 mRNA expression or ET-1-ir among experimental groups A, B, and C. Arterial plasma ET-1 was increased only in group A, the reperfused group.(ABSTRACT TRUNCATED AT 250 WORDS)

Selectivity of [125I]-PD151242 for human, rat and porcine endothelin ETA receptors in the heart

1. Endothelin-1 binds with high affinity to heart where it acts as a potent positive inotropic agent. Our aim was to characterize the labelled and unlabelled ETA-selective antagonist PD151242 in heart tissues derived from man, rat and pigs by use of radioligand binding techniques. 2. Binding of [125I]-PD151242 to sections of human left ventricle was time-dependent and reached equilibrium after 120 min at 23 degrees C with an association rate constant of 0.0235 min-1 nM-1. The binding was reversible at 23 degrees C with a dissociation rate constant of 0.00144 min-1. 3. Saturation binding assays with [125I]-PD151242 revealed a single population of high affinity ET receptors in human left ventricle (KD = 1.07 +/- 0.08 nM; Bmax = 29.8 +/- 4.2 fmol mg-1 protein), porcine left ventricle (KD = 1.92 +/- 0.27 nM; Bmax = 493 +/- 248 fmol mg-1 protein), and rat heart (KD = 0.64 +/- 0.08 nM; Bmax = 82.34.7 fmol mg-1 protein). 4. Unlabelled PD151242 competed with specific [125I]-ET-1 binding to human left ventricle tissue in a biphasic manner with high affinity binding to the ETA-site (KD = 7.21 +/- 2.83 nM) and lower affinity for the ETB-subtype (KD = 104 +/- 23 microM), indicating a greater than 10000 fold selectivity to the high affinity site. 5. The ETA-selective ligand FR139317 competed for [125I]-PD151242 binding in human left ventricle with nanomolar affinity (KD = 0.37 +/- 0.10 nM), whereas the ETB-selective compound, BQ3020, competed with only micromolar affinity (KD = 1.5 +/- 0.26 microM). 6. The novel ETA-selective radioligand [125I]-PD151242 binds with high affinity to human, rat and porcine heart. In human tissue, binding was shown to be reversible and highly selective for the ETA-subtype making [1251]-PD151242 a useful selective radioligand for further characterization of the ETA-receptor in human tissue.

Role of Na(+)-H+ exchange in mediating effects of endothelin-1 on normal and ischemic/reperfused hearts

Endothelin (ET) has been shown to be elevated under conditions of cardiac pathology and to produce diverse cardiac effects, including coronary constriction and a positive inotropic influence. We characterized the concentration- and time-dependent effects of the most potent of the ET isoforms, ET-1 (0.4, 2, and 4 nmol/L), on myocardial contractility and coronary resistance and assessed its effects on the ischemic and reperfused heart. Because ET-1 has been shown to activate the Na(+)-H+ exchanger in cardiac myocytes, we determined the contribution of the antiport by examining the effects of ET-1 in the presence of the Na(+)-H+ exchange inhibitor methylisobutyl amiloride (MIA). At all three concentrations, ET-1 produced an initial positive inotropic effect that was reversed with continued perfusion, the degree of the reversal being dependent on ET-1 concentration. With 0.4 nmol/L, contractility returned to pre-ET-1 values, whereas after 75 minutes of perfusion with 4 nmol/L ET-1, contractility was depressed by 75%. At all concentrations, ET-1 produced a coronary-constricting effect, whereas an elevation in resting tension was observed only with 4 nmol/L ET-1. MIA significantly prevented the positive inotropic effect of ET-1 but had no effect on loss in function or elevation in resting tension produced by 4 nmol/L ET-1. Furthermore, MIA partially, but not significantly, attenuated the constricting effects of all ET-1 concentrations. In the ischemic heart, 0.4 nmol/L ET-1 appeared to delay the loss in contractility produced by cessation of flow, although the effect was not significant. Higher concentrations of ET-1 were without effect on ischemia-induced contractile depression, although their presence produced a marked elevation in resting tension during ischemia that was attenuated by MIA. Recovery in contractility was reduced by all concentrations of ET-1, although the effects of the lowest concentration were associated primarily with defective relaxation. The depressant effects of ET-1 either in normal or ischemic/reperfused hearts were irreversible. The inhibitory effects of ET-1 on contractile recovery were associated with diminished tissue glycogen and elevated lactate levels. High-energy phosphates after reperfusion were depressed in hearts treated with 4 nmol/L ET-1. The attenuation in contractile recovery and alterations in metabolite content were prevented by MIA. These results provide evidence that ET-1 produces complex effects on heart function that are likely mediated via different mechanisms and demonstrate its ability to aggravate ischemic and reperfusion injury through a mechanism possibly involving Na(+)-H+ exchange activation.

Endothelin and myocardial ischemia

Endothelin is a potent vasoconstrictor with a wide range of effects on the heart. Changes in myocardial and circulating levels of endothelin have been described in various experimental models of myocardial ischemia, and in humans with acute myocardial infarction and different forms of angina pectoris. The role played by endothelin in the different states of myocardial ischemia is unclear. However, myocardial damage has been shown to be reduced in several experimental models of myocardial infarction by administering agents that block the action of endothelin. The aim of this review article is to present the current literature concerning the interaction between endothelin and the various forms of myocardial ischemia, and to explore the significance of such interactions.

Increased production of endothelin-1 in the hypertrophied rat heart due to pressure overload

Endothelin-1 (ET-1) has been demonstrated to induce hypertrophy in cultured cardiac myocytes. We investigated the production of ET-1 in the heart of aorta-banded rats in vivo. Seven days after the banding of the abdominal aorta, rats developed a significant left ventricular hypertrophy. The tissue content of mature ET-1 and the level of expression of prepro ET-1 mRNA were higher in the left ventricle of aorta-banded rats than in those of sham-operated rats. The expression of prepro ET-1 mRNA in the right ventricle was not different between the two groups. These findings indicate that the production of ET-1 increased in the hypertrophied left ventricle, thereby suggesting the possible involvement of endogenous ET-1 in the development of cardiac hypertrophy due to pressure overload.