REGULATION OF ANTERIOR PITUITARY FUNCTION BY POMC

The long-term objectives of this proposal are to elucidate the mechanisms by which hypothalamic beta-endorphin (beta-EP) regulates reproductive function. Beta-EP is responsible for the suppression of GnRH release which occurs under a variety of physiological and pathological conditions. The accumulatiing evidence supports a role of beta-EP in mediating the suppressive effects of sex stroids, stress, and hyperprolactinemia on GnRH and LH release. The specific aims of this proposal focus on the regulation of proopiomelanocortin (POMC) synthesis, release and processing in brain by sex steroids, corticotropin releasing hormone (CRH), and prolactin. Sex steroids appear to regulate brain beta-EP at several levels and brain beta-EP in turn participates in the feedback regulation of sex steroids on LH secretion. In the first part of this proposal the effects of sex steroids on POMC mRNA levels in the hypothalamus of individual rats will be determined by the use of a recently developed sensitive solution hybridization assay. Changes in POMC mRNA levels and POMC peptide content will be correlated with changes in the release of POMC peptides and GnRH into rat portal blood and to changes in the posttranslational processing of POMC as determined by use of HPLC and RIAs for several POMC peptides. In the second part of this proposal the effects of chronic intracerebroventricular administration of CRH on hypothalamic POMC peptide content, mRNA levels, and release of POMC peptides into portal blood will be determined in the rat and correlated with changes in hypothalamic GnRH and plasma LH levels. The ability of beta-EP antagonism to reverse any CRH- induced changes will also be studied. The demonstration of an interaction between CRH and brain POMC and GnRH would be important in furthering the understanding of the suppressive effects of stress on reproduction. Finally, the effets of experimentally induced hyperprolactinemia on POMC peptide content and mRNA levels will be studied in the hypothalamus of the rat and related to changes in GnRH and LH levels. The ability of beta-EP antagonism to reverse these changes will also be examined. In hyperprolactinemic patients the effects of chronic treatment with the long-acting oral opiate antagonist naltrexone on the pituitary-gonadal axis will be studied. In addition to providing important new information about the mechanism by which prolactin exerts its well-documented but incompletely understood inhibition of reproductive function, these studies could result in a potential new medical treatment for the hypogonadism produced by hyperprolactinemia.