Inhibition of renin secretion by intrarenal alpha-adrenoceptor blockade.

This study was designed to determine whether renal alpha-adrenoceptors can mediate tonic neural stimulation of renin secretion. The effect of alpha-adrenoceptor blockade by phenoxybenzamine (POB) or prazosin on renin secretion rate (RSR) was studied in pentobarbital-anesthetized dogs in which renal perfusion pressure was held constant with an adjustable aortic clamp. POB alone (100 micrograms.kg-1.min-1 iv) did not change arterial plasma renin activity (PRA). However, when beta-adrenoceptors were blocked by intravenous propranolol, intravenous POB infusion (100 micrograms.kg-1.min-1) decreased PRA and RSR to 48 +/- 8 and 21 +/- 9% of previous levels within 30 min. This effect was abolished by acute bilateral renal denervation. Direct intrarenal POB infusion (10 or 3.3 micrograms.kg-1.min-1) decreased RSR, whereas intravenous POB (3.3 micrograms.kg-1.min-1) had no effect on either RSR or PRA in propranolol-pretreated dogs. Prazosin (1 microgram.kg-1.min-1 iv) also significantly decreased PRA. These data indicate that when beta-adrenoceptors are blocked by propranolol, tonic neural stimulation of renin secretion is mediated by renal alpha-adrenoceptors.