17-BETA-ESTRADIOL INHIBITS THE PRODUCTION OF DOPAMINE BY THE TUBEROINFUNDIBULAR DOPAMINERGIC-NEURONS OF THE MALE-RAT

Previous work in our laboratory suggests that the indirect stimulation of prolactin gene transcription observed in male rats between 3 and 6 h following estrogen injection results from an inhibition of dopamine release from the tuberoinfundibular dopaminergic neurons. To evaluate further the role of dopamine in the regulation of prolactin gene tran scription by estrogens, we have examined the acute effects of 17 beta- estradiol (E(2)) on dihydroxyphenylalanine accumulation in the arcuate median eminence region and the amount of dopamine associated with the arcuate median eminence region. Dihydroxyphenylalanine accumulation i n the arcuate median eminence region was unaffected when examined 2 h following a single injection of E(2) (10 mu g), and was reduced by 60% when examined 4 h following E(2) treatment. When examined 4 h after E (2) injection, dopamine content in the arcuate median eminence region was significantly increased. These data suggest that estrogens exert a cute inhibitory effects on the tuberoinfundibular dopaminergic neurons of the male rat, and further support the assertion that the indirect stimulatory actions of estrogens on prolactin gene transcription resul t from inhibition of hypothalamic dopamine production.