Effects of estrogen on prolactin and tuberoinfundibular dopaminergic neurons.

Serum prolactin concentrations and dopamine turnover in the striatum and median eminence were studied in male rats after the administration of estradiol benzoate. The alpha-methyltyrosine-induced reduction of dopamine concentrations in these brain regions was used to evaluate relative rates of turnover. Steady state dopamine concentrations in the median eminence and striatum were not altered by 1, 3 or 5 days of estradiol treatment. However, 3 or 5 days of estradiol administration enhanced dopamine turnover in the median eminence but not in the striatum. Estradiol treatment failed to alter dopamine turnover in the median eminence of hypophysectomized rats. Estradiol increased serum prolactin concentrations at all of the times examined. Although alpha-methyltyrosine also increased serum prolactin, this increase was further enhanced in estradiol-treated rats. The increased prolactin response to alpha-methyltyrosine and increased dopamine turnover in the median eminence of estradiol-treated rats suggests that tuberoinfundibular dopaminergic neurons may be part of a hormonal-neuronal negative feedback loop which functions to regulate prolactin secretion.