Interactions between hypothalamic and peripheral hormones in the control of prolactin secretion.

The absence of nerve terminals in the anterior pituitary gland offers the possibility of studying a pure population of dopamine (DA) receptors. This study is facilitated by the use of anterior pituitary cells in primary culture, which permit the measurement of a precise parameter under typical dopaminergic control, namely prolactin secretion. On the other hand, since DA is the main hypothalamic factor controlling prolactin secretion, in vivo changes of plasma prolactin levels can be used as an index of DA release from the hypothalamus. Treatment with estrogens not only stimulates basal prolactin secretion but also can reverse the inhibitory effect of DA on prolactin secretion in vivo and in vitro. As assessed by the increased plasma prolactin levels following administration of a maximal dose of the DA antagonist thioproperazine, estrogens increase DA release from the hypothalamus. Progesterone, although inactive alone, can reverse the effect of estrogens on prolactin secretion both in vivo and in vitro. Under the same experimental conditions, dihydrotestosterone exerts inhibitory effects on spontaneous prolactin secretion and can reverse the stimulatory effects of estrogens.