Differential effects of rat endothelin on regional blood flow in the cat

Regional vascular responses to rat endothelin were investigated in the anesthetized cat. Intravenous injection of the peptide in doses of 0.1-1 nmol/kg decreased arterial pressure and increased distal aortic blood flow with a small secondary reduction in flow at the high dose. Mesenteric blood flow was decreased, and the decreases in flow were proportionately greater than the decreases in pressure so that mesenteric resistance increased at all doses. The rat peptide increased blood flow or caused biphasic changes in flow in the renal vascular bed. At 0.1 and 0.3 nmol the peptide decreased renal resistance, whereas at 1 nmol a biphasic change occurred. The present data suggest that responses to rat endothelin are dependent on dose and the vascular bed studied and indicate that the peptide can cause both vasodilation and vasoconstriction.