title: Effects of hypothyroidism on gonadal function after transition of short day photoperiod in male golden hamsters (Mesocricetus auratus).
abstract: Thyroid hormones permit the annual reproductive transition of seasonal breeders. Although, precise function of thyroid hormones in seasonal breeding is not well understood. In the present study, we examined effects of hypothyroidism on the hypothalamus-pituitary-gonadal axis in adult male golden hamsters after transition of the short-day photoperiod (SD; 8 h light: 16 h dark) condition. We confirmed that hypothyroid, which had been induced by administration of thiouracil in drinking water for 4 weeks, did not have direct effects on testes in male hamsters under the long-day photoperiod. Plasma concentrations of free T3 and T4 decreased 15 weeks after transition of SD condition. Plasma concentrations of testosterone in the hypothyroid group decreased earlier than in the control group after the transition from LD to SD. In animals treated with testosterone after castration, plasma concentrations of LH in the hypothyroid group decreased earlier than in the control group after the transition of SD. On the other hand, pituitary response to GnRH for LH release did not change in castrated hamsters as a result of hypothyroidism. These results suggest that thyroid hormones act the hypothalamus and might be required to maintain GnRH secretion in male golden hamsters.
authors.affiliation: Department of Basic Veterinary Science, The United Graduate School of Veterinary Sciences, Gifu University, Japan.
authors.forename: Erina
authors.initials: E
authors.lastname: Saita
authors.forename: Atsushi
authors.initials: A
authors.lastname: Tohei
authors.forename: Wan Zhu
authors.initials: WZ
authors.lastname: Jin
authors.forename: Shinji
authors.initials: S
authors.lastname: Takahashi
authors.forename: Akira K
authors.initials: AK
authors.lastname: Suzuki
authors.forename: Gen
authors.initials: G
authors.lastname: Watanabe
authors.forename: Kazuyoshi
authors.initials: K
authors.lastname: Taya
mesh_terms: D000728:Androgens / Q000097:blood / Q000494:pharmacology; D000818:Animals; D006224:Cricetinae; D005640:Follicle Stimulating Hormone / Q000097:blood; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology; D007030:Hypothalamo-Hypophyseal System / Q000502:physiology*; D007037:Hypothyroidism / Q000503:physiopathology*; D007986:Luteinizing Hormone / Q000097:blood; D008297:Male; D008647:Mesocricetus; D009919:Orchiectomy; D017440:Photoperiod; D010913:Pituitary-Adrenal System / Q000502:physiology*; D013737:Testis / Q000187:drug effects / Q000502:physiology*; D013739:Testosterone / Q000097:blood / Q000494:pharmacology; D013961:Thyroid Gland / Q000502:physiology
chemical_list: D000728:Androgens; D007987:Gonadotropin-Releasing Hormone; D013739:Testosterone; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone