LHRH ACTION: ROLES OF CA2+, PHOSPHOLIPIDS, AND ARACHIDO

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The stimulation of LH and FSH secretion by LHRH is the result of a complex series of biochemical reactions. Some of these are known, but the integration of these events is incomplete. Recently, LHRH has been shown to stimulate the series of biochemical reactions designated as the phosphatidylinositol (PI) cycle. Moreover, recently there have been reports that are suggestive that LHRH-stimulated LH secretion requires the formation of oxygenated metabolites of arachidonic acid (AA). This project has been designed to investigate specifically the LHRH-induced biochemstry and physiological consequences of the stimulation of the PI cycle and AA metabolism. In addition, the studies described in this proposal will consider the interrelation of the PI cycle and its metabolites. AA and its metabolites and other LHRH-related intracellular events such as Ca2+ mobilization and protein phosphorylation. All of these biochemical and physiological events lead to secretion of LH from the gonadotroph. These studies should provide insight into the control of hormone secretion in general as well as open new directions for research into the physiology and metabolism and the eicosanoids. The study proposed uses both biochemical and physiological methodologies to accomplish its primary goal of relating the biochemical mechanisms involved in the physiological response (LH secretion) to LHRH stimulation of LH and FSH secretion. Anterior pituitary cells are to be studied in a short cell culture (1 to 4 days). During the culture period the cells will be used to study the effects of LHRH on PI metabolism, AA metabolism, Ca2+ homeostasis and protein phosphorylation. Two primary metabolites of the PI cycle, appear from preliminary experiments, to be key for study: 1) diacylglycerol (DAG) and 2) AA. The involvement of DAG will be sutdied with respect to its roles in 1) the PI cycle; 2) protein kinase C activation and 3) as a source of AA. Arachidonic acid metabolism will be investigated to ascertain its LHRH-induced epoxygenation products and their roles in Ca2+ homeostasis and LH secretion. In particular, new AA-derived compounds which are apparently produced only during LHRH-stimulation of the gonadotroph will be structurally identified and their physiological importance ascertained. In summary this proposal approaches the study of hormone secretion of both the physiological and biochemical levels with a goal of adding information to pre-existing knowledge of the mechanism of LHRH-stimulated LH secretion.