Mechanism of action of luteinizing hormone-releasing hormone in rat ovarian cells

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Abstract
The initial step in the signal transduction of luteinizing hormone-releasing hormone (LHRH) in rat ovarian cells is the hydrolysis of membrane polyphosphoinositides into inositol phosphates and 1,2-diacylglycerol. The former compounds, especially inositol 1,4,5-triphosphate, are known to cause the release of calcium from intracellular stores, while diacylglycerol is a potent activator of protein kinase C. LHRH causes a rapid and transient increase in intracellular concentrations of free calcium ions, by approximately 4.5-fold, in the majority of granulosa cells as assessed by fura-2 microspectrofluorimetry. Like LHRH, a calcium ionophore (A23187) and activators of protein kinase C attenuate the steroidogenic response of the cells to follicle-stimulating hormone, but enhance the formation of gonadotropin-induced prostaglandin formation. These results support the concept that stimulation of polyphosphoinositide hydrolysis is intimitely involved in the direct action of LHRH at the level of the ovary.Key words: signal transduction, calcium, protein kinase C, ovary, steroid hormones.

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