The aim of the present study was to investigate the possibility that catecholaminergic pathways within the central nervous system play a role in the control of renin secretion. Plasma renin activity (PRA) was measured after intravenous administration of L-dopa with and without prior inhibition of extracerebral dopa decarboxylase by carbidopa (MK-486) in pentobarbital-anesthetized dogs in which changes in renal perfusion pressure were minimized by means of a suprarenal aortic clamp. When L-dopa (20 mg/kg ) was administered intravenously without carbidopa. PRA and blood pressure increased. In contrast, administration of L-dopa (20 mg/kg i.v.) after blockade of extracerebral, but not cerebral dopa decarboxylase by intravenous carbidopa (20 mg/kg), produced significant decrease in both PRA and blood pressure. Larger doses of l-dopa (30-50) mg/kg i.v.) also lowered both PRA and blood presure in three carbidopa-treated animals, whereas a smaller dose of L-dopa (10 mg/kg i.v.) significantly lowered blood pressure but not PRA. In dogs with both kidneys acutely denervated, L-dopa (20 mg/kg i.v.) with carbidopa lowered arterial pressure but did not consistently alter PRA. These data suggest that catecholamines formed within the central nervous system can act to lower renin secretion as well as blood pressure.