Effect of glutamine and nucleosides on prolactin secretion in the rat

The effect of glutamine and some nucleosides (cytidine and uridine) on basal and stimulated prolactin release was investigated in vivo and in vitro. Acute injection of glutamine did not modify serum prolactin concentration, both in basal and stimulated conditions; conversely repeated administrations of the aminoacid significantly reduced (p less than 0.05) the prolactin surge which occurs at 04:00 p.m. in male rats as well as that induced by the injection of the dopamine antagonist sulpiride. The hypoprolactinemic effect of glutamine was significantly potentiated by uridine and cytidine, which per se were not effective. No significant change in prolactin release was observed when anterior pituitary glands were incubated in presence of the above mentioned drugs. However, repeated in vivo injections of glutamine, uridine and cytidine were able to potentiate the inhibitory effect of dopamine on prolactin release in vitro. These results suggest that both glutamine and the nucleosides cytidine and uridine may influence the activity of the hypothalamic-hypophyseal-prolactin axis, probably via an interference with endogenous neurotransmitters.