Changes in the effect of gamma-aminobutyric acid on prolactin secretion during sexual maturation in female rats.

To evaluate the effects of the gamma-aminobutyric acid (GABA)ergic system on PRL secretion during sexual development in female rats, aminooxyacetic acid (an inhibitor of GABA-transaminase which increases the hypothalamic GABA concentration) was administered to 12- to 16- and 30-day-old female rats. The increased GABA level in the hypothalamus was accompanied by a significant increase in the serum PRL concentration in rats 16 days of age and a decrease in the serum concentration of the hormone in 30-day-old rats. No changes in PRL levels were observed at 12 days of age. Muscimol, a GABA-A receptor agonist, increased serum PRL concentrations in 16-day-old rats. By contrast, in rats 30 days of age, muscimol induced a significant decrease in PRL levels. On the other hand, the administration of baclofen, a GABA-B receptor agonist, induced a pattern of PRL modification similar to that observed with muscimol, i.e. stimulation in rats 16 days of age and inhibition in 30-day-old rats. These findings indicate that both the stimulatory and inhibitory effects of the GABAergic system on PRL secretion during sexual maturation are mediated by GABA-A and GABA-B receptors. The present results show that during sexual maturation there is a qualitative modification of the effect of the GABAergic system on PRL secretion. These findings could be related to the complex neuroendocrine mechanisms involved in the onset of puberty in the female rat.