title: Roles of estradiol and gonadotropin-releasing hormone in controlling negative and positive feedback associated with the luteinizing hormone surge in ovariectomized pigs.
abstract: Ovariectomized gilts (n = 63) were given estradiol benzoate (estradiol), antiserum to neutralize endogenous GnRH, and pulses of a GnRH agonist (GnRH-A) to stimulate release of LH. GnRH-A was given as 200-ng pulses hourly from 0 to 54 h and as 100- or 200-ng pulses every 30 or 60 min from 54 to 96 h after estradiol. Estradiol alone suppressed LH from 6 to 54 h and elicited an LH surge that peaked at 72 h. When GnRH-A was given every 30-60 min from 0 to 96 h, estradiol suppressed LH for 6-12 h, but then LH returned to pre-estradiol concentrations. When pulses of GnRH-A were given only between 54 and 96 h after estradiol, the surge of LH was related positively to dose and frequency of GnRH-A. We conclude that 1) estrogen acts at the hypothalamus to inhibit release of GnRH for 54 h and then causes a synchronous release of GnRH; 2) estrogen acts at the pituitary to block its response to GnRH for 6-12 h and enhances the accumulation of releasable LH; and 3) magnitude of the LH surge is dependent on the amount of GnRH stimulation.
authors.affiliation: Department of Animal Science, North Carolina State University, Raleigh 27695-7621.
authors.forename: J H
authors.initials: JH
authors.lastname: Britt
authors.forename: K L
authors.initials: KL
authors.lastname: Esbenshade
authors.forename: A J
authors.initials: AJ
authors.lastname: Ziecik
mesh_terms: D000818:Animals; D004958:Estradiol / Q000097:blood / Q000494:pharmacology*; D005246:Feedback; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000031:analogs & derivatives* / Q000276:immunology / Q000494:pharmacology / Q000502:physiology*; D007116:Immunization, Passive; D007700:Kinetics; D007986:Luteinizing Hormone / Q000378:metabolism*; D010052:Ovariectomy; D013552:Swine / Q000502:physiology*
chemical_list: D007987:Gonadotropin-Releasing Hormone; D004958:Estradiol; D007986:Luteinizing Hormone