Gonadotropin-Releasing Hormone Receptor Binding and Pituitary Responsiveness in Estradiol-Primed Monkeys

Anterior pituitary tissue from ovariectomized cynomolgus macaques ( Macaca fascicularis ) contains a single class of high-affinity receptor for gonadotropin-releasing hormone (GnRH). Exogenous estradiol causes a twofold increase in the tissue concentration of GnRH receptor within 36 hours without affecting receptor affinity. Release of luteinizing hormone in response to exogenous GnRH is initially suppressed by estradiol, but pituitary responsiveness is restored within 36 hours of introduction of estradiol. The pituitary tissue concentration of GnRH receptor is positively correlated with estradiol-induced release of luteinizing hormone only during the phase of potentiated response, an indication that although the augmentation of responsiveness by estradiol may reflect an increased GnRH receptor concentration, the suppression of the luteinizing hormone response by estradiol probably reflects estradiol actions at loci other than the pituitary GnRH receptor.