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, diureticstimulated, 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.

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