Effects of Hypothyroidism on Gonadal Function after Transition of Short Day Photoperiod in Male Golden Hamsters (Mesocricetus auratus)

Erina SAITA, Atsushi TOHEI, Wan Zhu JIN, Shinji TAKAHASHI, Akira K. SUZUKI, Gen WATANABE, Kazuyoshi TAYA
2005 Journal of reproduction and development  
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
more » ... rinking 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. Key words: Hypothyroidism, Male hamsters, Short day photoperiod, LH, Testosterone (J. Reprod. Dev. 51: [221][222][223][224][225][226][227][228] 2005) hyroid hormones appear to play a permissive role in the annual reproductive transition of a number of seasonal breeders in mammal and avian. I n b i r d s w h i c h a r e l o n g d a y b r e e d e r s , thyroidectomy prevents refractoriness developing a n d t h e y r e m a i n i n a b r e e d i n g c o n d i t i o n indefinitely under long days [1] [2] [3] . In mammals, the thyroid gland is necessary for seasonal reproductive suppression in the red deer [4, 5] and the sheep [6, 7] . In all these seasonal breeders, thyroidectomy results in prolongation of the breeding condition after the transition of a nonbreeding environment. Therefore, thyroid hormones are required for gonadal involution. Previous studies demonstrated that thyroid hormones need to terminate the breeding season at the appropriate time [8] [9] [10] [11] and the site which
doi:10.1262/jrd.16057 pmid:15699585 fatcat:tqhwksjvlrfyxbgjxyeqypsby4