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

Plasma renin activity, arterial and venous angiotensin II (A II) concentrations, and plasma aldosterone concentration were measured in 16 normal subjects (mean age = 34 years) after 8 hours of recumbency, following 2 hours of ambulation, and again 30 minutes after administration of furosemide intravenously. Measurements were obtained during periods of sodium restriction and again during sodium 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 recumbency on high sodium intake to values of 23.9 +/- 4.1 and 26.5 +/- 6.2 pg/ml, respectively, following intravenous furosemide during sodium restriction. Corresponding values for aldosterone exhibited a 5-fold rise from 5.6 ng/100 ml to 32.0 ng/100 ml, whereas plasma renin 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 hour to 13.1 ng/ml per hour. Despite the disparity in the magnitude of these increases, significant correlations were identified between all four 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 less than 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 sodium restriction.