Reciprocal Influence of Salt Intake on Adrenal Glomerulosa and Renal Vascular Responses to Angiotensin II in Normal Man

Abstract

The adrenal glomerulosa cell and the renal vasculature respond to similar arterial angiotensin II (A II) levels. We have assessed the effect of decreased sodium intake on their responses to A II in man. Studies were performed in 42 normal subjects in balance on a daily intake of 100 meq potassium and either 200 or 10 meq sodium/day. Renal blood flow was measured with (133)Xe and arterial A II, renin and aldosterone concentrations by radioimmunoassay. A II was infused intravenously (1, 3, or 10 ng/kg/min) for 40-60 min; 14 subjects received graded doses. The A II level increased linearly with dose and plateaued within 3 min; blood pressure and renal vascular resistance showed a similar time-course. Aldosterone rose within 10 and plateaued within 20 min. Dose-response relationships were established between the rate of A II infusion and the adrenal, the renal vascular, and pressor responses. Sodium restriction reduced the pressor (P < 0.01) and the renal vascular response (P < 0.01), but potentiated the adrenal response to A II (P < 0.01). An excellent correlation was found between the plasma A II and aldosterone levels, but the slope of their regression relationship on a high (y = 0.13x + 6) and low salt intake (y = 0.32x + 14) differed significantly (P < 0.0005). Thus, sodium intake reciprocally influences vascular and adrenal responses to A II: salt restriction blunts the vascular response and potentiates the adrenal's, a physiologically important influence in view of aldosterone's role in sodium conservation.