Effect of repeated doses of L-5-hydroxytryptophan and carbidopa on prolactin and aldosterone secretion in man.

To evaluate changes in serum prolactin and plasma and urine aldosterone after a serotonergic challenge, 8 healthy men (19 to 42 yr), taking dexamethasone (0.75 mg qid), received the serotonin precursor L-5-hydroxytryptophan (L5HTP; 100 mg qid) with the peripheral decarboxylase inhibitor carbidopa (C; 50 mq qid) or matching placebos in a randomized, crossover manner. Serum prolactin concentration increased in all subjects after L5HTP/C in comparison to placebo, mean (SD) prolactin (ng/ml) at 8 h after dosing was 19.8 ± 6.3 after L5HTP/C and 12.0 ± 3.1 after placebo (p < 0.05). In contrast, in comparison to values on placebo, L5HTP/C had no apparent effect on mean plasma concentration at all observation times; mean (SD) aldosterone (ng/dl) at 8 h after dosing was 12.0 ± 5.1 and 12.0 ± 3.8 after placebo (NS). Mean (SD) urinary aldosterone (μg/24 h), Na+(mEq/24 h) and K+(mEq/24 h) excretion were 7.0 ± 4.4,49.3 ± 30.6, 30.1 ±11.2, after L5HTP/C and 7.4 ± 5.8, 59.7 ± 23.9, 33.3 ± 7.4 after placebo (NS). Under these study conditions, subacute serotonergic stimulation with oral L5HTP/C resulted in prolactin but not aldosterone release.