No Effect of Short Term Angiotensin II Infusion on Plasma Renin Substrate Levels in Man*

Abstract

We studied the effect of angiotensin II (A-II) infusion (4 ng/kg BW.min) on plasma renin substrate (RS) levels and PRA in five normal men during normal, diuretic-stimulated, and enalapril-interrupted function of the renin-angiotensin system. A-II infusion increased (15-25%) both systolic and diastolic blood pressure in the normal state and during angiotensin-converting enzyme inhibition, whereas the increase during diuretic-stimulated renin-angiotensin system function was less. The plasma RS concentration was measured by both direct and indirect RIA. The mean basal plasma RS levels, measured with direct assay, were 1516 +/- 150 (SE) in the normal state, 1566 +/- 150 after diuretic administration, and 1650 +/- 133 nmol/L after enalapril administration. The corresponding mean basal plasma RS levels measured with the indirect assay were 1073 +/- 100, 1031 +/- 57, and 902 +/- 78 nmol/L, respectively. Plasma RS levels did not change during or after the A-II infusions, whereas PRA decreased significantly in all experimental conditions. The results suggest that A-II exerts no direct stimulatory effect on hepatic release of RS. Thus, A-II appears not to be important in the short term regulation of plasma RS levels.