A large body of evidence suggests that the synthesis1,2 and secretion3-7 of the pituitary hormone prolactin is inhibited by the hypothalamic hormone dopamine. The finding that dopamine inhibits adenylate cyclase activity of rat pituitary8 and human prolactin-secreting adenoma9 suggests that the dopaminergic inhibition of prolactin synthesis may be mediated by decreased levels of cyclic AMP. Recently, the dopaminergic inhibition of prolactin synthesis has been shownto involve decreased concentrations of prolactin mRNA2,10. Further more, monobutyryl cyclic AMP increases prolactin mRNA levels in pituitary cells treated with the potent dopaminergic agonist ergocryptine11. Such changes in prolactin mRNA levels could involve transcriptional or post-transcriptional events. Here we report that treatment of pituitary cells with ergocryptine leads to rapid inhibition of prolactin gene transcription and that addition of monobutyryl cyclic AMP to ergocryptine-pretreated cells results in a rapid stimulation of prolactin gene transcription.
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