title: Gonadotroph responsiveness in orchidectomized sheep: IV. Effect of estradiol infusion during the breeding and anestrous seasons.
abstract: The interaction between estradiol (E2) and season on gonadotroph function was assessed in orchidectomized sheep (wethers). Wethers in the breeding (November) or anestrous (May) season received E2 (in 20% ethanol-saline [vehicle]) by continuous infusion at rates of 0.31, 1.25, 5, or 20 micrograms/h (n = 6 wethers/group). Controls received vehicle alone. Gonadotroph responsiveness (LH release induced by 500 ng GnRH, i.v.) was assessed at the end of the 48-h infusion period. Mean serum concentrations of E2 at the end of infusion were < 0.6 pg/ml in animals receiving vehicle, and 2.5 +/- 0.3, 10.7 +/- 0.4, 35.1 +/- 0.9, and 86.1 +/- 4.1 pg/ml in animals receiving 0.31, 1.25, 5, and 20 micrograms E2/h, respectively. Mean serum concentrations of LH and FSH, the amplitude and frequency of LH secretion, and gonadotroph responsiveness did not differ (p > 0.05) with season in controls. Infusion of E2 at 5 or 20 micrograms/h decreased (p < 0.05) serum concentrations of LH and FSH and eliminated episodic secretion of LH, regardless of season. Conversely, E2 infusion at 0.31 microgram/h resulted in significant suppression of gonadotropin secretion in May, but not November. Similarly, the reduction in serum concentrations of LH and FSH induced by E2 infusion at 1.25 micrograms/h was more pronounced (p < 0.05) in May than November. Compared to gonadotroph responsiveness in controls, responsiveness in the breeding, but not the anestrous, season increased (p < 0.05) after infusion of 0.31 microgram E2/h.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Animal Science, University of California, Davis 95616-8521, USA.
authors.forename: H
authors.initials: H
authors.lastname: Sakurai
authors.forename: B M
authors.initials: BM
authors.lastname: Adams
authors.forename: T E
authors.initials: TE
authors.lastname: Adams
mesh_terms: D000780:Anestrus; D000818:Animals; D004958:Estradiol / Q000097:blood / Q000494:pharmacology*; D005260:Female; D005640:Follicle Stimulating Hormone / Q000097:blood* / Q000235:genetics; D037201:Follicle Stimulating Hormone, beta Subunit; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology; D007986:Luteinizing Hormone / Q000097:blood* / Q000235:genetics / Q000378:metabolism; D008297:Male; D009919:Orchiectomy; D010902:Pituitary Gland / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D011966:Receptors, LHRH / Q000378:metabolism; D012098:Reproduction; D012621:Seasons; D012756:Sheep
chemical_list: D037201:Follicle Stimulating Hormone, beta Subunit; D012333:RNA, Messenger; D011966:Receptors, LHRH; D007987:Gonadotropin-Releasing Hormone; D004958:Estradiol; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone