EFFECT OF L-DOPA ON PLASMA-RENIN ACTIVITY WITH AND WITHOUT INHIBITION OF EXTRACEREBRAL DOPA DECARBOXYLASE IN DOGS

Abstract

Plasma renin activity (PRA) was measured after i.v. 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 suprarenal aortic clamp. When L-dopa (20 mg/kg) was administered i.v. without carbidopa, PRA and blood pressure increased. L-dopa (20 mg/kg i.v.) administration after blockade of extracerebral, but not cerebral dopa decarboxylase by i.v. carbidopa (20 mg/kg), significantly decreased PRA and blood pressure. Larger L-dopa (30-50 mg/kg i.v.) doses lowered PRA and blood pressure in 3 carbidopa-treated animals: a smaller L-dopa (10 mg/kg i.v.) dose 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. Apparently catecholamines formed within the CNS can act to lower renin secretion and blood pressure.