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

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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.