title: Neuroendocrine mechanisms that control seasonal changes of luteinizing hormone secretion in sheep are sexually differentiated.
abstract: The apparent earlier onset of seasonal breeding activity of adult male versus adult female sheep suggests that the neuroendocrine mechanisms that control onset of the breeding season may be sexually differentiated in this species. However, it is difficult to compare gradual onset of testicular growth to abrupt changes in ovarian activity. To determine the relative timing of seasonal transitions in neuroendocrine reproductive activity, we compared temporal changes of LH concentrations in adult, gonadectomized, estradiol (E)-treated (experiment 1), or testosterone (T)-treated (experiment 2) Suffolk male and female sheep held outdoors for 18 mo. In addition, we compared the rates at which E-treated males and females become photorefractory to a winter solstice hold (WSH) photoperiod. In all three experiments, blood samples were collected weekly. In addition, serial blood samples were collected every 12 min for 4 h at approximately 2-mo intervals for experiment 1 and at monthly intervals for experiment 2. Neither plasma E nor T concentrations differed (p > 0.05) between sexes. In E-treated animals, mean LH changed (p < 0.001) over time in both sexes, and there was a sex x time interaction (p < 0.001). LH pulse amplitude changed (p < 0.001) over time in both sexes, but there was no detectable (p > 0.05) sex x time interaction. LH pulse frequency varied significantly over time in E-treated females (p < 0.001) but not in males (p < 0.05). The amplitude of the annual oscillation of mean LH was greater (p < 0.01) in E-treated females than in males.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Veterinary Biosciences, University of Illinois at Urbana-Champaign 61801.
authors.forename: L S
authors.initials: LS
authors.lastname: Lubbers
authors.forename: G L
authors.initials: GL
authors.lastname: Jackson
mesh_terms: D000818:Animals; D004958:Estradiol / Q000097:blood / Q000494:pharmacology; D005260:Female; D007986:Luteinizing Hormone / Q000378:metabolism*; D008297:Male; D009919:Orchiectomy; D010052:Ovariectomy; D012621:Seasons; D012727:Sex Characteristics; D012756:Sheep / Q000502:physiology*; D013739:Testosterone / Q000097:blood / Q000494:pharmacology
chemical_list: D013739:Testosterone; D004958:Estradiol; D007986:Luteinizing Hormone