Progesterone Action on Hypothalamic Lhrh Neurons: In Vitro and In Vivo Studies
The present study examined the effect of progesterone (P) on hypothalamic luteinizing hormone-releasing hormone (LHRH) neurons, as estimated by in vitro (superfusion) and in vivo (push-pull perfusion) techniques. The administration of P unequivocally stimulated the release of LHRH from hypothalamic tissue obtained from ovariectomized, estradiol-primed (OVX + E) rats as well as proestrous rats. The salient features of these findings are summarized as follows: (1) P was capable to stimulate LHRH release only when the steroid was delivered in an intermittent mode (10 min-on, 20 min-off; 10 ng/ml). A continuous infusion of P at a similar low concentration (10 ng/ml) was ineffective in modifying the release of LHRH. (2) The estrogen-priming was an obligatory requirement for the in vitro P-stimulated LHRH release and this in vivo priming of E upon the responsiveness of the neural LHRH secretary apparatus appears to be dose-dependent. (3) During the rat estrous cycle, P stimulated LHRH release solely in hypothalamic fragments derived from proestrous, but not from the other stages of the estrous cycle, and (4) It was evident that a prostaglandin E(,2) activity and a cyclic AMP-generating system was involved in the P-stimulated LHRH release.
University of Illinois - Urbana-Champaign
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University of Illinois at Urbana-Champaign