Renal Vascular Responses to Angiotensin and Norepinephrlne in Normal Man

The effect of sodium intake on renal vascular responses to angiotensin and norepinephrine infused intra-arterially was assessed in normal man by xenon washout. In subjects on an unrestricted diet, the dose of angiotensin inducing a 50% reduction in mean blood flow (EDS0) was 38.2 ± 12.6 ng/min, a hundredfold lower dose than that for norepinephrine. Sodium restriction reduced the sensitivity to angiotensin tenfold: the EDfi0 rose to 378 ± 12 ng/min. This diet, conversely, potentiated responses to norepinephrine: the threshold dose fell from 37 ± 10 to 3.6 ± 1.9 ng/min. Thus, the reduction in sensitivity to angiotensin induced by sodium restriction was not a nonspecific effect on the vascular smooth muscle. Sodium restriction also reduced the variability in the vascular response to angiotensin, and a close correlation was found between urine sodium content and angiotensin responsiveness. The blood vessels of the normal human kidney are remarkably sensitive to angiotensin: the threshold dose is approximately 1 ng/min for intra-arterial infusion. Circulating angiotensin may be a mediator of renal vascular tone, but circulating catecholamines probably play a minimal role.