ARTERIAL AND VENOUS EFFECTS OF ATRIAL-NATRIURETIC-PEPTIDE IN THE HUMAN FOREARM

Atrial natriuretic peptide (ANP) has direct vasodilating properties in addition to its diuretic and natriuretic effects. Furthermore, vascular permeability may be influenced. Because relatively little is known about the venous and capillary actions of ANP in humans, we investigated the spectrum of vascular actions of ANP in the human forearm. In seven healthy subjects, ANP was infused intraarterially in consecutive doses of 0, 10, 50, and 250 ng/100 mL tissue/min together with vehicle or norepinephrine 1 ng/kg/min. In seven other subjects, 0.5 ng/kg/min angiotensin II and 10 ng/kg/min serotonin were used as a constrictor. Venous occlusion plethysmography was used to measure forearm blood flow, venous compliance, capillary filtration rate, and maximum venous outflow. Intraarterial infusion of ANP induced a dose-dependent increase of forearm blood flow but the relative increases were not influenced by concomitant vasoconstriction. Venous compliance was not affected by the infusions, but serotonin and angiotensin II decreased the changes of both forearm volume and venous pressure. ANP antagonized these effects of angiotensin II. Capillary filtration rate was not affected by ANP infusion. ANP alone had no effect on the maximum venous outflow, but it attenuated the decrease induced by norepinephrine and angiotensin II. These results indicate that in the human forearm ANP has predominantly arterial effects, whereas the venous actions become manifest only in the presence of vasoconstriction. The venous effect of ANP may therefore gain importance in disease states with elevated levels of vasoconstrictors, for instance, in congestive heart failure.