Key Laboratory of Animal Physiology, Biochemistry and Molecular Biology of Hebei Province, College of Life Sciences, Hebei Normal University, Shijiazhuang, China.
Functional Laboratory, Experimental Center for Teaching, Hebei Medical University, Shijiazhuang, China.
Front Endocrinol (Lausanne). 2020 May 29;11:303. doi: 10.3389/fendo.2020.00303. eCollection 2020.
Reproduction is an energetically costly phenomenon. Therefore, to optimize reproductive success, male birds invest enough energetic resources for maintaining well-developed testes. The hypothalamic-pituitary-thyroid (HPT) axis in birds can crosstalk with the hypothalamic-pituitary-gonadal (HPG) axis, thus orchestrating both the reproduction and metabolism. However, until now, how the free-living birds timely optimize both the energy metabolism and reproduction via HPT-axis is not understood. To uncover this physiological mechanism, we investigated the relationships among body mass, testis size, plasma hormones including thyroid-stimulating hormone (TSH), thyroxine (T), triiodothyronine (T), metabolites including glucose (Glu), triglyceride (TG), total cholesterol (TC), uric acid (UA), diencephalon mRNA expressions of type 2 () and 3 () iodothyronine deiodinase enzymes, thyrotropin-releasing hormone (), thyroid-stimulating hormone (, gonadotropin-releasing hormone (, and gonadotropin-inhibitory hormone () in a male Eurasian tree sparrow (ETS, ). We found significantly larger testis size; elevated diencephalon and mRNA expressions, plasma T, and UA levels; and significantly lowered Glu, TG, and TC levels during mating relative to the non-mating stages in male ETSs. However, , and mRNA expression did not vary with the stage. Furthermore, life-history stage dependent variation in plasma T had both direct effects on the available energy substrates and indirect effects on body mass and testis size, indicating a complex regulation of metabolic pathways through the HPT- and HPG-axes. The identified differences and relationships in mRNA expression, plasma T and metabolites, and testis size in male ETSs contribute to our understanding how free-living birds adjust their molecular, endocrinal, and biochemical features to orchestrate their reproductive physiology and metabolism for the maintenance of well-developed testes.
繁殖是一个能量消耗巨大的现象。因此，为了优化繁殖成功率，雄性鸟类会投入足够的能量资源来维持发育良好的睾丸。鸟类的下丘脑-垂体-甲状腺（HPT）轴可以与下丘脑-垂体-性腺（HPG）轴相互作用，从而协调生殖和代谢。然而，到目前为止，自由生活的鸟类如何通过 HPT 轴及时优化能量代谢和生殖还不得而知。为了揭示这一生理机制，我们研究了体重、睾丸大小、包括促甲状腺激素（TSH）、甲状腺素（T）、三碘甲状腺原氨酸（T）在内的血浆激素、包括葡萄糖（Glu）、甘油三酯（TG）、总胆固醇（TC）、尿酸（UA）在内的代谢物、二叠体 2 型（）和 3 型（）甲状腺素脱碘酶酶的 mRNA 表达、促甲状腺激素释放激素（）、促甲状腺激素（，促性腺激素释放激素 （，和促性腺激素抑制激素（）在雄性欧亚树麻雀（ETS，）中的关系。我们发现，在交配期间，雄性 ETS 的睾丸大小显著增大；二叠体 和 mRNA 表达、血浆 T 和 UA 水平升高；而 Glu、TG 和 TC 水平显著降低。然而， 和 mRNA 表达并没有随着阶段的变化而变化。此外，血浆 T 的生活史阶段依赖性变化对可用能量底物既有直接影响，又对体重和睾丸大小有间接影响，表明通过 HPT 和 HPG 轴对代谢途径进行了复杂的调节。雄性 ETS 中 mRNA 表达、血浆 T 和代谢物以及睾丸大小的差异和关系有助于我们理解自由生活的鸟类如何调整其分子、内分泌和生化特征，以协调其生殖生理学和代谢，维持发育良好的睾丸。
