The long term objective of our studies in the understanding of the regulation of pituitary gonadotropin secretion.
The aim of the present reseach plan is to delineate the intracellular events following LHRH-receptor interaction that lead to the release of the gonadotrophins, luteinizing hormone and follicle stimulating hormone, from the pituitary gland. The primary experimental model will be the cyclic female rat adenohypophysis superfused in a continuous flow system in vitro. Concurrently the sheep adenohypophyseal pars tuberalis as an enriched gonadotrope tissue will be developed as an additional model. The physiology of immediate release of gonadotropins (secretion that occurs with minutes following LHRH-receptor interaction) will be established by determining the relative contributions made by increased flux of Ca++ across the plasma membrane and consequent increase in intracellular [Ca++] and that made by induction of a non-extracellular-Ca++ second messenger which requires Ca++ for its subsequent action. Initial biochemical characterization of the componets of this cascade will involve examination of membrane phospholipids, phospholipidactivated protein kinase and Ca-binding protein. The second or subsequent phase of the release process which occurs under certain hormonal conditions and which is temporally distinct is LHRH self-priming. We will investigate the intracellular signals resulting from LHRH-receptor interaction which elicit the increase in protein synthesis required for expression of the self-priming response. The relationship between LHRH self-priming and protein synthesis-dependent augmentation in response to cyclic nucleotides or to alterations in the ionic environment will be established in order to identify the intracellular signal(s) and the protein(s) being synthesized. For both aspects of gonadotropin secretion, i.e. immediate release and the self-priming response, analysis of changes in gonadotropin secretory rates will be a major indicator in the superfusion system. Other selected endpoints to be considered are activity changes in cyclic nucleotide- and Ca++ regulated enzymes, phosphatidylinositol turnover, changes in phospholipid activated kinase, LHRM-induced specific protein phosphorylation and ion-induced as compared to LHRH-induced changes in total protein amino acid incorporation.
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