CENTRAL AND REGIONAL HEMODYNAMIC-EFFECTS DURING INFUSION OF BIG ENDOTHELIN-1 IN HEALTHY HUMANS

Big endothelin-1 (Big ET-1) was given intravenously to six healthy men to study uptakes and vascular effects. Blood samples were taken from systemic and pulmonary arterial and internal jugular and deep forearm venous catheters. Arterial Big ET-1-like immunoreactivity (Big ET-1-LI ) increased from 5.43 +/- 0.60 to 756 +/- 27 pmol/l, and ET-1-LI incre ased from 4.67 +/- 0.08 to 6.67 +/- 0.52 pmol/l (P < 0.001). Skeletal muscle fractional extraction of Big ET-1-LI was 15 +/- 4%. ET-1-LI rel ease did not increase in the studied vascular beds. Heart rate fell by 17% (P ( 0.001), cardiac output fell by 26% (P < 0.001), and stroke v olume fell by 11% (P < 0.05). Mean arterial blood pressure increased 1 8%, systemic vascular resistance increased 65%, and pulmonary vascular resistance increased 57% (P < 0.01-0.001). Pulmonary blood pressures, forearm blood flow, arterial pH, arterial PCO2, and systemic arterial -internal jugular venous O-2 difference remained unchanged. No specifi c Big ET-1 receptors were found in human pulmonary membranes. The half -maximal inhibitory concentration for the receptor antagonist bosentan was 181 nM. In summary, circulating Big ET-1 elicits greater increase s in mean arterial blood pressure and systemic vascular resistance and decreases in heart rate and cardiac output compared with an equimolar ET-1 infusion (26).