The principal objectives of this proposal are to study the control of anterior pituitary function by brain pro-opiomelanocortin (POMC) derived peptides and to study the regulation of these peptides in brain by sex steroids. Specifically, the control of prolactin (PRL) and LH secretion by hypothalamic Beta-EP, Beta-EP(1-27), Alpha-MSH and CLIP will be studied and the hypothesis that some POMC fragments function as endogenous opioid antagonists will be examined. The ability of Beta-EP (1-27), Alpha-MSH and CLIP, injected intraventricularly in the rat, to competitively antagonize the stimulation of PRL or the suppression of LH produced by Beta-EP will be tested. Rats will be passively immunized with antisera to Alpha-MSH and CLIP to determine if these peptides participate in the physiological regulation of anterior pituitary function. The site of action and mechanism by which these peptides inhibit PRL release will be studied in the pituitary stalk sectioned monkey. The fact that several peptides from the same precursor have opposite effects on hormone secretion suggests that differential post-translational processing of POMC in the hypothalamus serves as an important regulator of anterior pituitary function. The regulation by sex steroids of the synthesis and post-translational processing of POMC in the hypothalamus and the secretion of POMC derived peptides into hypophyseal portal blood will therefore be studied. Beta-EP, Alpha-MSH and CLIP will be measured in monkey hypophyseal portal blood throughout the menstrual cycle and correlated with GnRH levels in portal blood. Beta-EP in monkey third ventricular CSF will be evaluated as an index of hypothalamic Beta-EP secretion and correlated with portal blood Beta-EP levels. In the rat, the effects of castration and sex steroids on Beta-EP, Alpha-MSH and CLIP concentrations will be studied in the median eminence and medial basal hypothalamus. Ion exchange chromatography will be performed to determine if sex steroids alter the processing of Beta-EP to its biologically active form. The effects of sex steroids on the synthesis of POMC will be studied by blocking axonal transport with colchicine and measuring the accumulated Beta-EP immunoactivity in parikarya in the arcuate nucleus where Beta-EP is synthesized. Alternatively, POMC biosynthesis will be studied by intraventricular infusion of labeled amino acids and immunoprecipitation. The results of these studies should clarify how Beta-EP and other POMC derived peptides interact to control PRL and LH secretion and how sex steroids may regulate LH secretion in part by affecting the synthesis and processing of POMC in the hypothalamus.
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|Wardlaw, S L; Smeal, M M; Markowitz, C E (1986) Antagonism of beta-endorphin-induced prolactin release by alpha-melanocyte-stimulating hormone and corticotropin-like intermediate lobe peptide. Endocrinology 119:112-8|
|Wardlaw, S L (1986) Regulation of beta-endorphin, corticotropin-like intermediate lobe peptide, and alpha-melanotropin-stimulating hormone in the hypothalamus by testosterone. Endocrinology 119:19-24|