RENAL AND ENDOCRINE RESPONSES TO A RENIN INHIBITOR, ENALKIREN, IN NORMAL HUMANS

Interpretation of renin-angiotensin blockade with angiotensin coverting enzyme inhibitors is potentially confounded by their multiple effects. We used a selective renin inhibitor (enalkiren, A-64662) to explore the renal and endocrine effects of angiotensin II in healthy men. Each received 90-minute enalkiren infusions at 2-day intervals, on a low (10 mmol, 16 subjects) and high (200 mmol, 12 subjects) salt diet. Plasma renin activity, immunoreactive plasma angiotensin II and aldosterone concentrations, inulin, and p-aminohippurate clearance were measured by standard methods. Plasma renin activity fell at 0.1-mu-g/kg, but the threshold for biologic effect was 256-mu-g/kg, where plasma immunoreactive angiotensin II and aldosterone concentration fell, and renal plasma flow rose (p < 0.01). The maximal renal vascular response (+152 +/- 23 ml/min/1.73 m2) occurred at 512-mu-g/kg (p < 0.01). Diastolic and mean blood pressure fell modestly but significantly (p < 0.05). Responses were limited on a high salt diet. We confirm that conventional plasma renin activity measurement is misleading in humans receiving a renin inhibitor. The renal vascular response to renin inhibition in this study appeared to substantially exceed reported responses to angiotensin converting enzyme inhibition, perhaps reflecting a crucial and relatively inaccessible intrarenal locus.