Effects of changing gonadotropin-releasing hormone pulse frequency and estrogen treatment on levels of estradiol receptor-α and induction of Fos and phosphorylated cyclic adenosine monophosphate response element binding protein in pituitary gonadotropes: Studies in hypothalamo-pituitary disconnected ewes

Abstract

Estrogen receptor-α (ERα) levels in gonadotropes are increased during the follicular phase of the ovine estrous cycle, a time of increased frequency of pulsatile secretion of GnRH and elevated plasma estrogen levels. In the present study, our first aim was to determine which of these factors causes the rise in the number of gonadotropes with ERα. Ovariectomized hypothalamo-pituitary disconnected ewes (n = 4-6) received ihe following treatments: 1) no treatment, 2) injection (im) of 50 μg estradiol benzoate (EB), 3) pulses (300 ng iv) of GnRH every 3 h, 4) GnRH treatment as in group 3 and EB treatment as in group 2, 5) increased frequency of GnRH pulses commencing 20 h before termination, and..