Arterial and venous angiotensin II in normal subjects. Relation to plasma renin activity and plasma aldosterone concentration, and response to posture and volume changes.

Abstract

Plasma renin activity, arterial and venous angiotensin II (A II) concentrations and plasma aldosterone concentration were measured in 16 normal subjects (mean age = 34 yr) after 8 h of recumbency, following 2 h of ambulation and again 30 min after furosemide administration i.v. Measurements were obtained during periods of Na restriction and again during Na surfeit. Both arterial and venous A II exhibited a 3-fold increase from low values of 8.8 .+-. 2.5 and 8.6 .+-. 2.5 pg/ml of plasma, respectively, during recubency on high Na intake to values of 23.9 .+-. 4.1 and 26.5 .+-. 6.2 pg/ml, respectively, following i.v. furosemide during Na restriction. Corresponding values for aldosterone exhibited a 5-fold rise from 5.6 ng/100 ml to 32.0 ng/100 ml; plasma renine activity (PRA) measured by an in vitro assay exhibited a 20-fold rise from 0.6 .+-. 0.2 ng of angiotensin I (AI) generated per ml per h to 13.1 ng/ml per h. Despite the disparity in the magnitude of these increases, significant correlations were identified between all 4 of the measured parameters, indicating a major role of the renin-angiotensin system in regulating aldosterone output in response to volume and posture-related stimuli. Values of arterial and venous immunoreactive A II were closely correlated (r = +0.72, P < 0.005), but significant differences were demonstrated between low and high salt periods, suggesting that changes in metabolism of A II in the peripheral circulation may occur during Na restriction.