To investigate the role of the central and peripheral dopaminergic systems in the control of the renin-angiotensin-aldosterone system in conscious rats, dopamine or its antagonist, metoclopramide, was injected intravenously (i.v.) and intracerebroventricularly (i.c.v.). Dopamine (100 micrograms/kg), when injected i.c.v., decreased plasma renin activity (PRA) and plasma aldosterone concentration (PA), while metoclopramide (50 micrograms/kg, i.c.v.) increased both of them. Intravenous administration of dopamine (1 microgram/kg/min) did not produce significant changes in either PRA or PA. In contrast, metoclopramide (500 micrograms/kg, i.v.) increased PA, which was not accompanied by any change in PRA. Blood pressure was decreased by i.c.v. administration of dopamine and increased by i.c.v. injection of metoclopramide, whereas no change in blood pressure was observed when these compounds were administered i.v. Dopamine and metoclopramide, injected i.v. or i.c.v., did not produce significant changes in plasma sodium, potassium and corticosterone concentrations. These results suggest that the dopaminergic system in the brain regulates renin secretion, thereby changing PA. In contrast, dopamine receptors of the adrenal glands may inhibit aldosterone secretion, which is not mediated by changes in the renin-angiotensin system, plasma potassium and ACTH.