PROGESTERONE STIMULATES GNRH GENE-EXPRESSION IN THE HYPOTHALAMUS OF OVARIECTOMIZED, ESTROGEN-TREATED ADULT-RATS

Gonadotropin-releasing hormone (GnRH) is a major neural signal for hyp othalamic control of gonadotropin secretion which in turn influences g onadal steroid synthesis. Progesterone (P) is known to affect release and content of GnRH. The action mechanism of P on GnRH mRNA level rema ins, however, to be resolved. Here we report that P augments GnRH mRNA level in hypothalamic tissues derived from ovariectomized, estradiol- treated adult rats. The stimulatory action of P was time-dependent and lasted at least for 9 h. When RU486, a P receptor antagonist, was adm inistered 1 hr before P treatment, it clearly blocked the stimulatory action of P on GnRH mRNA level. These results strongly suggest that P regulates GnRH gene expression in the rat hypothalamus, presumably thr ough the P receptor-mediated mechanism.