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INHIBIN INCREASES AND PROGESTERONE DECREASES RECEPTORS FOR GONADOTROPIN-RELEASING HORMONE IN OVINE PITUITARY CULTURE
Citation:
Laws, S., M. Beggs, AND W. Miller. INHIBIN INCREASES AND PROGESTERONE DECREASES RECEPTORS FOR GONADOTROPIN-RELEASING HORMONE IN OVINE PITUITARY CULTURE. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/J-90/178.
Description:
The effects of progesterone (P4) and inhibin on gonadotropin-releasing hormone receptor number (GnRH-R) and binding affinity were investigated using ovine pituitary cells in culture. ollowing treatment with P4 or porcine inhibin, GnRH binding was analyzed using a radioligand-receptor assay with des-Gly10-[D-Ala6]-LHRH-ethylamide (GnRH-A) as the radiolabeled GnRH superagonist analog and as competing ligand. retreatment of cultures with P4 for 24 or 48 h decreased GnRH-A binding by 44% and 72%, respectively. reatment with enriched porcine inhibin (ED50 = 0.8 ug/ml) or highly purified bovine inhibin (ED50 = 0.6 ng/ml) increased GnRH-A binding greater than 2-fold. his increase correlated with an increased LH response to GnRH and was reversed within 24 h of inhibin removal. catchard analysis indicated that GnRH-R binding affinity was not changed by inhibin after 48 h (K9 = 4 + 1 x 10 9 M-1) as compared with the control (Ka = 8 + 4 x 10 9 M-1)> owever, GnRH-R number was significantly increased (16 x 10 3 GnRH-R/gonadotroph) when compared with the control (2 x 10 3 GnRH-R/gonadotroph). hese data indicate the (1) treatment of ovine pituitary cultures with P4 and inhibin can modulate GnRh binding by as much as 8-fold, and (2) changes in GnRH binding appear to account for changes observed in GnRH responsiveness in ovine pituitary cultures after P4 or inhibin treatment. herefore, these in vitro studies suggest a potential mechanism by which endogenous P4 and inhibin may play a role in the regulation of GnRH action in vivo.