Messenger ribonucleic acid for gonadotropin-releasing hormone receptor and numbers of gonadotropin-releasing hormone receptors in ovariectomized ewes after hypothalamic-pituitary disconnection and treatment with estradiol.

To study the regulation of ovine GnRH receptors in the absence of GnRH, hypothalamic input was removed by hypothalamic-pituitary disconnection (HPD). Steady-state concentrations of GnRH receptor mRNA and numbers of GnRH receptors were measured after HPD and subsequent treatment with estradiol. Anterior pituitary glands were collected 24 (n = four), 36 (n = two), 48 (n = four), and 72 h (n = four) after HPD. An additional group of ewes received subcutaneous implants of estradiol 24 h after HPD, and pituitary glands were collected 0 (n = four), 12 (n = four), 24 (n = three), and 48 h (n = four) after exposure to estradiol. Pituitary glands were also obtained from four ovariectomized ewes that did not undergo HPD (OVX controls). At 24 h after HPD, mean number of GnRH receptors had decreased (P < .05) by 73%; however, mean concentration of GnRH receptor mRNA was not different from OVX controls. Relative to HPD ewes, treatment with estradiol increased mean concentrations of GnRH receptor mRNA and mean numbers of GnRH receptors (P < .01 and P < .001, respectively). From these data we conclude that 1) acute removal of GnRH decreases the numbers of GnRH receptors but does not affect steady-state concentrations of GnRH receptor mRNA and 2) estradiol increases the numbers of GnRH receptors and steady-state concentrations of GnRH receptor mRNA via direct effects at the level of the pituitary gland.