Effect of γ-Aminobutyric Acid on Growth Hormone and Prolactin Secretion in Man: Influence of Pimozide and Domperidone*

Abstract

To investigate the possibility that GH [growth hormone] release induced by .gamma.-aminobutyric acid (GABA) in man is mediated by a dopaminergic mechanism, the effect of 2 antidopaminergic compounds, pimozide and domperidone, on the plasma GH response to acute GABA administration (5 g orally) was evaluated. Only the former compound can freely cross the blood-brain barrier. In 9 normal volunteers, GABA caused a significant increase of plasma GH levels (P < 0.0001 vs. GH levels in a group of 14 controls). In these subjects, pimozide (6 mg/day orally, for 4 days) significantly blunted the GH elevation induced by GABA (P < 0.01). Unlike pimozide, in 8 additional subjects, domperidone (4 mg injected i.v. immediately before GABA administration) did not influence the GABA-induced GH response. GABA did not alter either baseline or pimozide-stimulated plasma PRL [prolactin] levels. It did not significantly modify the brisk PRL rise after domperidone injection. GABA-stimulated GH secretion apparently is mediated via dopamine release at a suprapituitary level. With regard to PRL secretion, no GABA-dopamine interactions are readily apparent.