title: Estradiol and progesterone influence the synthesis of gonadotropins in the absence of gonadotropin-releasing hormone in the ewe.
abstract: Acute actions of estradiol and progesterone on synthesis and secretion of gonadotropins without the confounding effects of endogenous steroids and GnRH were examined by using the ovariectomized (OVX), hypothalamic-pituitary-disconnected (HPD) ewe. Thirty-two OVX ewes were subjected to HPD and randomly assigned to eight groups (4 ewes/group). An additional four OVX ewes served as controls. Each of 12 OVX-HPD ewes received 4 s.c. implants of estradiol 24 h after HPD (implantation was designated as Time 0 h). Sixteen OVX-HPD ewes received no treatment and served as contemporary controls. The remaining four OVX-HPD ewes received implants of estradiol for 48 h and were administered 16 mg progesterone i.m. twice daily in the last 24 h of estradiol treatment. Blood samples and pituitary glands were collected from OVX-HPD control and steroid-treated ewes at 0, 12, 24, and 48 h. Amounts of gonadotropin subunit mRNAs and serum concentrations of gonadotropins were decreased at 24 h after HPD and remained unchanged thereafter in OVX-HPD controls. Although treatment with estradiol decreased pituitary content of LH and steady-state levels of mRNA for LH beta-subunit (p < 0.05) compared to contemporary controls, serum concentrations of LH were not affected. Serum concentrations and pituitary content of FSH decreased (p < 0.05) 24 h after initiating treatment with estradiol, but steady-state levels of FSH beta-subunit mRNA were unchanged. There was a transient decrease in pituitary content of FSH at 24 h of estradiol treatment. Steady-state levels of mRNA for alpha-subunit were unaffected by estradiol.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Physiology, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins 80523, USA.
authors.forename: G B
authors.initials: GB
authors.lastname: Di Gregorio
authors.forename: T M
authors.initials: TM
authors.lastname: Nett
mesh_terms: D000818:Animals; D004958:Estradiol / Q000494:pharmacology*; D005260:Female; D005640:Follicle Stimulating Hormone / Q000235:genetics / Q000378:metabolism; D037201:Follicle Stimulating Hormone, beta Subunit; D015292:Glycoprotein Hormones, alpha Subunit / Q000235:genetics; D007987:Gonadotropin-Releasing Hormone / Q000502:physiology*; D006065:Gonadotropins, Pituitary / Q000096:biosynthesis*; D013006:Growth Hormone / Q000235:genetics; D007031:Hypothalamus / Q000502:physiology / Q000601:surgery; D007986:Luteinizing Hormone / Q000235:genetics / Q000378:metabolism; D010052:Ovariectomy; D010902:Pituitary Gland / Q000502:physiology / Q000601:surgery; D011374:Progesterone / Q000494:pharmacology*; D012333:RNA, Messenger / Q000378:metabolism; D012756:Sheep / Q000378:metabolism*
chemical_list: D037201:Follicle Stimulating Hormone, beta Subunit; D015292:Glycoprotein Hormones, alpha Subunit; D006065:Gonadotropins, Pituitary; D012333:RNA, Messenger; D007987:Gonadotropin-Releasing Hormone; D011374:Progesterone; D004958:Estradiol; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone; D013006:Growth Hormone