Renin release and pressor response to renal arterial hypotension: effect of dietary sodium

Changes in plasma renin activity (PRA) and mean arterial pressure (MAP) produced by renal arterial hypotension were studied in conscious, adrenalectomized dogs maintained on low-, normal-, or high-Na diet during constant steroid replacement therapy. In animals maintained on a low-Na diet, reduction of renal perfusion pressure to 50 mmHg for 45 min increased MAP 40 +/- 3 (SE) mmHg, while PRA rose rapidly by 36.5 +/- 6 ng ml-1 h-1. Similar renal hypotension in dogs maintained on a normal-Na diet increased MAP only 21 +/- 3 mmHg while PRA rose 5.5 +/- 0.9 ng ml-1 h-1; dogs on high-Na intake had a 6 +/- 1 mmHg pressure rise without a significant change in PRA. The rise in MAP correlated well with the log deltaPRA. Calculated open-loop gain was -1.2, -0.7, and -0.1 in dogs on low-, normal-, and high-Na diets, respectively. Nonpeptide angiotensin I converting enzyme inhibitor (CEI) reversed the elevated MAP observed during reduction of renal perfusion pressure in dogs on low- and normal-Na diets, but had little effect in dogs on high-Na intake. These observations suggest that the renin-angiotensin system becomes quantitatively more important in the regulation of blood pressure as Na intake is reduced.