THE EFFECTS OF THE GABAERGIC DRUG, SODIUM VALPROATE, ON PROLACTIN SECRETION IN NORMAL AND HYPERPROLACTINEMIC SUBJECTS

To find out whether the .gamma.-aminobutyric acid (GABA)ergic system affects PRL [prolactin] secretion in humans, sodium valproate (DPA or Na-dipropyl-acetate), a drug inducing increase of endogenous GABA, was administered to 20 normal and 15 hyperprolactinemic subjects. PRL circulating levels were measured by radioimmunoassay in the samples obtained after acute oral treatment with 400 mg DPA. A significant decrease (P < 0.01) in comparison with basal levels was observed in normal women from 30-180 min after drug administration. DPA treatment also lowered blood PRL levels in hyperprolactinemic subjects (7 females) without evidence of pituitary tumor. A decrease very similar to the one found in normal subjects (P < 0.05 vs. basal levels) was observed within 180 min from drug ingestion. No significant changes were found after the same treatment in hyperprolactinemic patients with evidence of prolactinoma (7 females and 1 male). Pharmacological enhancement of endogenous GABAergic tone is followed by inhibition of PRL secretion. GABA may exert an inhibitory control on PRL release in humans. In hyperprolactinemic subjects, this GABAergic control appears to be present only when a pituitary tumor cannot be demonstrated.