Interference of dopamine infusion on gamma-amino butyric acid (GABA)-stimulated prolactin increase.

The effects of simultaneous iv administration of dopamine (DA) and gamma-amino butyric acid (GABA) were evaluated in 5 normal women. After injection of 50 mg GABA alone, PRL plasma concentrations showed a significant (p less than 0.02) rise. DA infusion (500 g/min over a 60 min period) significantly (p less than 0.02) decreased PRL plasma levels. When GABA was administered intravenously during DA infusion, the rise of PRL plasma concentrations, which was observed after injection of GABA alone, was suppressed. PRL circulating levels significantly (p less than 0.02) decreased as during infusion with DA alone. These results seem to support the hypothesis that stimulatory effects of GABA or its analogues on in vivo PRL secretion could be due to an inhibitory effect of these drugs on endogenous DA.