Stimulation of renin secretion by alpha-adrenoceptor agonists.

This study was designed to determine whether stimulation of intrarenal alpha-adrenoceptors can increase renin secretion rate (RSR) in the absence of increased renal vascular resistance and to identify the accompanying changes in renal function. Experiments were performed in pentobarbital-anesthetized dogs in which renal perfusion pressure was maintained at approximately 90 mmHg and the infused kidney was acutely denervated. Renal artery infusion of the alpha-adrenoceptor agonist methoxamine (0.5 microgram X kg-1 X min-1 for 30 min) increased RSR from 160 +/- 95 to 1,376 +/- 385 ng ANG I/min (P = 0.01) but did not decrease renal blood flow (RBF); the same dose infused intravenously had no effect on RSR or RBF. Intra-arterial phenylephrine infusion (0.5 microgram X kg-1 X min-1 for 9 min) increased RSR by 500 +/- 157 ng ANG I/min (P less than 0.01) and decreased both inulin clearance (Cin) and urinary sodium excretion (UNaV) by 25% but did not affect RBF. At a lower concentration of phenylephrine (0.2 microgram X kg-1 X min-1 for 9 min), RSR increased by 318 +/- 103 ng ANG I/min (P less than 0.01) and RBF, Cin, and UNaV did not change. The increase in RSR was completely blocked by prazosin but was unaffected by propranolol. In summary, renin secretion can be stimulated by activation of intrarenal alpha-adrenoceptors even in the absence of increased renal vascular resistance.