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

The effects of simultaneous iv administration of dopamine (DA) and γ-suamino butyric acid (GABA) were evaluated in 5 normal women. After injection of 50 mg GABA alone, PRL plasma concentrations showed a significant (p<0.02) rise. DA infusion (500 g/min over a 60 min period) significantly (p<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<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.