Ovariectomy-Evoked Increase in Gonadotropin Releasing Hormone Receptor Parallels Its Messenger RNA Level, but Does not Correlate with Stimulated Gonadotropin Release

Abstract

The amount of gonadotropin releasing hormone receptor (GnRH-R) in the anterior pituitary changes during the rat estrous cycle; in addition, it is chronically increased for several weeks in response to ovariectomy. The present study was undertaken to investigate these changes in relation to the concentrations of GnRH-R mRNA, gonadotropins and luteinizing hormone-β (LH-β) subunit in serum and the pituitary gland, as well as hypothalamic GnRH. GnRH-R concentrations on the day of estrus were significantly lower than that at diestrus (30% lower during 2d), its mRNA decreased even further (by 60%), but there were no significant changes in gonadotropin. Ovariectomy increased GnRH-R significantly (by 30% during 2wk) in parallel with receptor mRNA and with pituitary LH and LH-β, but induced an earlier increase in serum gonadotropins. Our results suggest that transcriptional activity is more intimately linked to the number of GnRH-R in the long-term increase after ovariectomy than in the short-term change during the estrous cycle, and that the increased GnRH-R is not a major factor in ovariectomy-stimulated gonadotropin release.