Cardiovascular effects of endothelin

Myocardial function and effect of serum in isolated heart from hypertriglyceridemic and hypertensive rats

We evaluated the myocardial function of rats with sugar-induced hypertriglyceridemia (HTG) and hypertension, and the effect of serum on myocardial performance in the isolated heart preparation. Also, the response to reperfusion after 30 minutes of global ischemia was investigated. Hearts from HTG rats developed lower ventricular pressure (VP) and the conduction rate was higher than in hearts from control rats (CR). The recovery of VP after ischemia was significantly lower in HTG than in CR hearts (p < 0.05). The HTG sera produced a higher increase in the VP and in the perfusion pressure. During reperfusion, the incidence of premature beats, ventricular fibrillation and tachycardia in HTG hearts was increased so hypertriglyceridemia caused alterations in the mechanical and electrical conduction of the myocardium and exacerbated the injury produced by ischemia-reperfusion. Also a circulating factor in the HTG serum induced a vasoactive response of the heart which was reflected in its mechanical performance.

Captopril does not acutely modulate plasma endothelin-1 concentration in human congestive heart failure

Congestive heart failure (CHF) is a syndrome characterized by increased levels of angiotensin II (Ang II) and endothelin-1 (ET-1). In vitro, Ang II stimulates ET-1 release. The purpose of the study was to assess the effect of a single dose of an angiotensin-converting enzyme inhibitor (ACEI) captopril versus placebo on plasma endothelin concentration in human congestive heart failure. Captopril (25 mg, given orally) was compared with placebo in a group of 20 patients with systolic dysfunction in a double-blind randomized study. Plasma irET concentration was significantly increased in CHF patients compared with normal subjects (5.59 pg/ml +/- 0.35 vs. 3.58 pg/ml +/- 0.99, p < 0.0002). Despite the decrease in systolic blood pressure and the increase in plasma renin activity, suggesting a significant blockade of the renin-angiotensin system, no difference in plasma irET-1 was observed between captopril and placebo. Our results suggest that captopril does not acutely influence irET-1 plasma concentration in human CHF. These data do not support the hypothesis that the acute vasodilator effect of a single dose of 25 mg of captopril given daily orally involves modulation of the increased plasma concentration of endothelin observed in CHF.

Pathophysiological significance of plasma endothelin in peripheral circulatory disturbances

Endothelin (ET) is produced in blood vessels and is a novel potent vasoconstrictor. Although the presence of immunoreactive ET in the circulating blood suggests that ET plays an important role in the regulation of systemic and/or local hemodynamics, the role of circulating ET has not been ascertained using human populations. We examined the values of the ET level and peripheral blood flow, including other biochemical and physiological factors, in 108 healthy adults who participated in annual health examinations of Japanese adults living in a rural community in 1992 and 1993. A small change in ET after the passage of one year showed good reproducibility of the value. ET was positively correlated with diastolic blood pressure (BP) and negatively with finger skin blood flow in healthy adults. Multiple regression analysis demonstreted that the positive relationship between ET and diastolic BP was independent of other health indicators. A detailed examination using optical spectroscopy for elderly institutionalized subjects without any trouble in the activity of daily living revealed a negative correlation of ET with saturated oxygen in blood, tissue hemoglobin volume and local blood flow and a positive one with the local oxygen extraction fraction. The present study indicated that increased ET in the elderly subjects was associated with hypoxia not only in the local finger skin region, but also possibly in the arterial tissue, suggesting that ET is involved in atherosclerosis. The negative correlation between ET and finger skin blood flow seen in the healthy adults may be induced by hypoxia. Although we recognized a positive correlation between ET and BP, the increase in ET seemed to be an outcome of elevation in BP rather than a cause of hypertension.

Change in digital blood flow with simultaneous reduction in plasma endothelin induced by hand-arm vibration

Involvement of endothelium-derived relaxing factor (EDRF) or endothelium-derived constricting factor (EDCF) has been proposed as the pathophysiologic mechanism of vibration-induced white finger (VWF). Recent evidence that endothelin is a potent vasoconstrictor peptide indicates that it may play a role in vasoregulation during vibration exposure through the local actions of EDRF or EDCF. Therefore, we examined the effects of grasping (50 N) and hand-arm vibration (50 m/s2 rms, 120 Hz, x-axis) on digital blood flow (DBF) and on the level of plasma endothelin in seven healthy male office workers. Grasping decreased DBF without affecting endothelin, and vibration increased DBF with a simultaneous reduction in endothelin. The grasping-induced decrease in DBF seemed to be due to mechanical compression of the vessels. The negative correlation between DBF and endothelin during vibration exposure suggests that a reduction in release of endothelin from smooth muscle into the vessel cavity during vibration leads to vasodilatation, possibly attributable to the local axon reflex.