Effects of N-methyl-D-aspartate and kainic acid on prolactin secretion in prepubertal female rats.

The control of prolactin (PRL) secretion by N-methyl-D-aspartate (NMDA) and kainic acid (KA), agonists of NMDA and kainate receptors, and the interactions between NMDA and KA with nitric oxide (NO) were analysed in prepubertal female rats. For this purpose, serum PRL concentrations and hypothalamic and pituitary dopamine (DA) and serotonin (5-HT) concentrations were measured in females injected with NMDA, KA or two blockers of NO synthase: Nw-nitro-L-arginine methyl ester (NAME) and Nw-nitro-L-arginine (NA). Also, the effects of combined administration of NMDA and KA with the blockers of NO synthase were analyzed. We found that PRL release was inhibited 15 min after NMDA and KA administration, an effect probably mediated through the release of hypothalamic DA, as shown by the higher pituitary DA concentrations after NMDA or KA administration. The inhibitory effect of NMDA was preceded by an increase in serum PRL levels, observed at 5 and 10 min after NMDA administration. Nw-Nitro-L-arginine methyl ester alone inhibited prolactin secretion, and both NAME and NA abolished the inhibitory effect of KA, but not that of NMDA. We conclude that administration of NMDA exerted a dual action on PRL secretion: initially DA release was inhibited, leading to an increase in PRL secretion that in turn stimulated DA release and decreased serum PRL concentrations. Kainic acid also inhibited PRL secretion by releasing DA, an effect blocked by NO synthase inhibitors.