Butachlor causes disruption of HPG and HPT axes in adult female rare minnow (Gobiocypris rarus)

• Butachlor may disrupt sex hormones synthesis in fish.
• Butachlor could disrupt homeostasis of TH by inactive deiodinase type 3.
• Butachlor could cause a complex arrangement of interacting endocrine axes.

Butachlor is a chloroacetamide herbicide widely used in Asia, and may enter the aquatic environment through agricultural application. In this study, plasma VTG and hormone levels (E2, 11-KT, T3 and T4) were determined after the female rare minnow (Gobiocypris rarus) was exposed to butachlor at environmental relevant concentrations (0, 0.1, 1, and 10 μg/L) for 40 days. The mRNA levels of the HPG axis-related genes (gnrh, erα, vtg, star, lhr, 3β-hsd, cyp11a, cyp17, cyp19a and cyp19b), and the HPT axis-related genes (trα, dio1, dio2, and dio3) were quantified after 20 and 40 days exposure to butachlor. For the HPG axis, the plasma 11-KT was increased at exposure concentration of 10 μg/L, and VTG was significantly decreased at 1 μg/L. Functional genes like gnrh and cyp19b in the brains, star, lhr, cyp11a, 3β-hsd, and cyp19a in the ovaries, and erα and vtg in livers were up-regulated. For the HPT axis, the results showed that plasma T4 levels were significantly increased, the gene expression of dio1 was up-regulated, dio2 showed no significant variation, and dio3 was down-regulated in the livers. These results indicated that butachlor may promote the accumulation of T4 in fish through inactive deiodinase type 3. The transcription of HPG axis-related genes could serve as an auto-regulation of hormone levels after exposure to butachlor. Furthermore, the activation of gnrh may play an important role as a feed-back mechanism in the regulation of hormone levels and crosstalk of endocrine axes.