College of Biological and Environmental Engineering, Zhejiang University of Technology, Hangzhou 310032, China.
Gen Comp Endocrinol. 2011 Feb 1;170(3):487-93. doi: 10.1016/j.ygcen.2010.11.001. Epub 2010 Nov 21.
Metolachlor (MT) is one of the most important pesticides applied to corn and other crops for controlling broadleaf and grass weeds. However, the effects of MT on the thyroid system in fish remain to be elucidated. In the present experiment, transcription of genes related to the thyroid system, including thyrotropin releasing hormone (Trh), deiodinase 2 (Dio2), thyroid hormone receptor α (Thrα), and thyroid hormone receptor β (Thrβ), were induced by MT in a sex-, developmental stage-, and tissue- specific manner when medaka were exposed to various concentrations of MT for 14 days. The transcriptional levels of the genes were only significantly altered in both juvenile and adult female medaka in response to MT exposure. And the lowest concentrations able to significantly induce transcription of the selected genes were 10 and 100 μg/L in juvenile and adult female medaka, respectively. In adult female medaka, a significant up-regulation of these genes was detected only in the brain, with little or no effect in the liver. Furthermore, MT-induced (100 μg/L) transcription of thyroid system-related genes was enhanced significantly in male juvenile medaka in the presence of estrogen (E2) (50 and 100 ng/L). Moreover, the mRNA levels of Thrα and Thrβ in males increase with the combined treatments of 100 μg/L MT and 100 ng/L E2. Dio2 increased when exposed to 100 μg/L MT and 50 or 100 ng/L E2. The information obtained in the present study suggests that MT has the potential to influence several steps of the hypothalamus-pituitary-thyroid (HPT) axis homeostasis and to disrupt the thyroid system in medaka.
甲草胺（MT）是一种重要的玉米和其他作物用农药，用于防治阔叶杂草和禾本科杂草。然而，MT 对鱼类甲状腺系统的影响仍需阐明。在本实验中，当鱼类在不同浓度的 MT 中暴露 14 天时，MT 以性别、发育阶段和组织特异性的方式诱导甲状腺系统相关基因的转录，包括促甲状腺激素释放激素（Trh）、脱碘酶 2（Dio2）、甲状腺激素受体α（Thrα）和甲状腺激素受体β（Thrβ）。只有在幼鱼和成年雌鱼中，这些基因的转录水平才会因 MT 暴露而显著改变。能够显著诱导所选基因转录的最低浓度分别为幼鱼和成年雌鱼 10 和 100μg/L。在成年雌鱼中，这些基因在大脑中显著上调，而在肝脏中几乎没有或没有影响。此外，在存在雌激素（E2）（50 和 100ng/L）的情况下，MT 诱导（100μg/L）的甲状腺系统相关基因转录在雄性幼鱼中显著增强。此外，随着 100μg/L MT 和 100ng/L E2 的联合处理，雄性鱼类中 Thrα 和 Thrβ 的 mRNA 水平增加。当暴露于 100μg/L MT 和 50 或 100ng/L E2 时，Dio2 增加。本研究获得的信息表明，MT 有可能影响下丘脑-垂体-甲状腺（HPT）轴稳态的几个步骤，并破坏鱼类的甲状腺系统。
