Inhibition of the renin-angiotensin-aldosterone system by L-dopa with and without inhibition of extracerebral dopa decarboxylase in man.

1. The present study was undertaken to investigate the possibility that central nervous system mono-aminergic pathways may play a role in the control of the renin-angiotensin-aldosterone system in man. 2. 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 four doses). 3. L-Dopa administration elicited a significant fall in plasma renin activity (PRA) (P less than 0.01 at 120, 150 and 180 min) and in plasma aldosterone levels (P less than 0.05 at 90, 120, 150 and 180 min); L-dopa plus carbidopa induced a decrease in PRA (P less than 0.05 at 120 and 150 min, P less than 0.01 at 180 min) and in plasma aldosterone concentration (P less than 0.05 at 30 and 60 min, P less than 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 two regimens. 4. Since L-dopa, as well as L-dopa plus carbidopa, has been shown to augment 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 central nervous system catecholamine levels.