Prolactin stimulates [3H]dopamine release from dispersed rat tubero-infundibular dopaminergic neurons and dopamine decreases gonadotropin-releasing hormone release induced by calcium ionophore.

In order to investigate the involvement of prolactin-dopamine and dopamine-gonadotropin interactions in the hypothalamo-pituitary axis of hyperprolactinemia, in vitro studies were performed using primary cultures of dispersed rat hypothalamic heterogeneous cells containing tubero-infundibular dopaminergic neurons or gonadotropin-releasing hormone (GnRH) neurons. We observed that prolactin caused dose-dependent stimulation of [3H]dopamine release after a 16-h incubation. Staurosporin (10 nmol/l), an inhibitor of protein kinase C, significantly reduced the [3H]dopamine release induced by prolactin (1 mg/l). Incubation of tubero-infundibular dopaminergic neurons with prolactin (1 mg/l) had no effect on intracellular cyclic adenosine monophosphate accumulation. Dopamine (1 mumol/l) significantly (p < 0.01) reduced the release of GnRH induced by 50 mumol/l calcium ionophore from dispersed hypothalamic cells from the preoptic area, while prolactin had no effect on GnRH release. These data support the hypothesis that the antigonadotropic effect of prolactin on the hypothalamus is mediated by an inhibitory effect of dopamine on GnRH release.