DOI: 10.13671/j.hjkxxb.2018.0464
"In this study, fluoride exposure showed a short-term inhibitory and long-term inducing effect on the expression of dio1 and dio2 genes, consistent with the trend of T4 content changes. Moreover, after 90 days of exposure, the T3 content increased significantly, which may be due to the enhanced expression of deiodinase genes induced by fluoride."
(Note time and dose-dependent bi-phasic effects)
To investigate the interfering effect of fluoride on the thyroid endocrine function of zebrafish, this study used adult female zebrafish as the research subjects. Different concentrations of fluoride (0, 20, 40, and 80 mg·L⁻¹) were exposed for 45 and 90 days. The growth and development index of the zebrafish was measured, and the thyroid tissue structure was observed microscopically using histological methods. The levels of T3 and T4 hormones in plasma were detected by enzyme-linked immunosorbent assay (ELISA), and the expression of endocrine-related genes on the HPT axis was detected by real-time quantitative PCR. The results showed that, compared with the control group, the growth and development index of female zebrafish in the fluoride-exposed group decreased with increasing exposure concentration and time (p<0.05); the severity of thyroid tissue lesions increased with increasing fluoride exposure concentration and duration; after 45 days of fluoride exposure, T3 and T4 levels increased, while after 90 days, T4 levels decreased, with a significant decrease in the 80 mg·L⁻¹ group (p<0.05); after 45 days of fluoride exposure, the expression levels of trh, tshβ, tg, nis, tpo, dio1, dio2, ttr and ugt1ab mRNA in the 40 mg·L⁻¹ and 80 mg·L⁻¹ fluoride exposure groups were significantly increased (p<0.05); after 90 days of exposure, the expression of all mRNAs except crh was significantly decreased in the 40 mg·L⁻¹ group (p<0.05), and the expression of all mRNAs except tg, nis, and ttr was significantly decreased in the 80 mg·L⁻¹ group (p<0.05). After 90 days of exposure, the mRNA expression levels of tg, dio1, and dio2 were significantly increased in both the 40 mg·L⁻¹ and 80 mg·L⁻¹ groups (p<0.05), while the expression of ugt1ab mRNA was significantly decreased in the 80 mg·L⁻¹ group (p<0.05). In conclusion, fluoride can interfere with the thyroid endocrine function of female zebrafish by affecting their growth and development, thyroid tissue structure, hormone levels, and the expression of endocrine-related genes along the HPT axis, thereby affecting the organism's growth and development. The results of this study provide theoretical data for the ecotoxicological effects and risk assessment of fluoride in aquatic environments.