GnRH-MEDIATED DESENSITIZATION OF THE PITUITARY GONADOTROPE IS NOT CALCIUM DEPENDENT

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Abstract
In the present work we describe homologous desensitization of gonadotropin release from pituitary cells in response to short-term exposure to GnRH. Like the release process itself, desensitization requires receptor occupancy by an agonist. In contrast, however, inhibition of LH release by chelation of extracellular calcium or blockade of the calcium ion channel does not inhibit desensitization. Further, stimulation of gonadotropin release by ionophore A23187 (which mobilizes calcium without GnRH receptor occupancy) does not lead to desensitization. These findings indicate that the decrease in pituitary sensitivity to GnRH due to an initial exposure to the peptide can be uncoupled from LH release. The data provide the first evidence of a calciumindependent biological effect of the releasing hormone in cultured pituitary cells.