Endothelin induces an initial increase in cardiac output associated with selective vasodilation in rats

The systemic and regional hemodynamic effects of endothelin (ET), a novel endothelial derived vasoconstrictor peptide were studied in Wistar Kyoto rats. A bolus of 1 nmol/Kg ET intravenously induced a transient 43% decrease in blood pressure associated with a 57% decrease in systemic resistance and a 30% increase in cardiac output (p<0.01 for all parameters). This was followed by an increase of 20% in arterial pressure and of 71% in systemic resistance and a decrease of 30% in cardiac output at 10 minutes. The initial fall in blood pressure was not abolished by pretreatment with verapamil, captopril, indomethacin, ketanserin, atropine, methylene blue or ethanol. Verapamil abolished the hypertensive phase by markedly decreasing cardiac output. ET had selective effects on the arterial tree; during the hypotensive phase it caused a transient increase in blood flow in the carotid and femoral arteries (+41% and +83% respectively, p<0.01) but a decrease in flow in the renal and mesenteric arteries (-53% and -44% respectively, p<0.05). Accordingly, there was a decrease in resistance in the carotid and femoral beds (-55% and -67% respectively, p<0.01) and an increase in resistance in the renal and mesenteric beds (+102 %; p<0.01 and +23%; p= N.S. respectively). Subsequently there was an increase in resistance in all vascular beds to variable degrees. The maximal increase in resistance was in the renal bed (+156 %). Thus, ET causes initally a potent systematic vasorelaxation and an increase in cardiac output later progressing to systemic vasoconstriction and a decrease in cardiac output. The initial vasolidation is selective, appearing in musculocutaneous beds but not in visceral beds.