INHIBITION OF THE RENIN-ANGIOTENSIN-ALDOSTERONE SYSTEM BY L-DOPA WITH AND WITHOUT INHIBITION OF EXTRA-CEREBRAL DOPA DECARBOXYLASE IN MAN

The possibility was studied that CNS mono-aminergic pathways may play a role in the control of the renin-angiotensin-aldosterone system in man. Eight normal subjects received in a randomized order placebo, L-dopa (500 mg, orally) and L-dopa (100 mg, orally) plus carbidopa (35 mg, orally) after pretreatment with carbidopa (50 mg every 6 h for 4 doses). L-Dopa administration elicited a significant fall in plasma renin activity (PRA) (P < 0.01 at 120, 150 and 180 min) and in plasma aldosterone levels (P < 0.05 at 90, 120, 150 and 180 min); L-dopa plus carbidopa induced a decrease in PRA (P < 0.05 at 120 and 150 min, P < 0.01 at 180 min) and in plasma aldosterone concentration (P < 0.05 at 30 and 60 min, P < 0.01 at 90 and 120 min), in comparison with placebo administration; between-drugs analysis revealed no difference in the decreases in PRA and plasma aldosterone levels induced by the 2 regimens. As L-dopa, and L-dopa plus carbidopa, augments catecholamine levels in the brain of various animal species, the present data suggest that in man PRA and plasma aldosterone concentration might be inhibited by increased CNS catecholamine levels.