Abstract: Xenopus tropicalis tadpoles (NF51) were exposed to TBT for 48 and 96 h, respectively. Exposures to 50 and 200 ng·L^-1 TBTCl showed no effects on the survival rate of tadpoles. The expression of TRβ and DI3 mRNA were significantly increased in the tails by 1～2.3 fold in the groups treated with 50 ng·L^-1 TBTCl. The expression of TSHβ mRNA was increased in the tails by 2 fold after 48 h of exposure. RXRα mRNA was decreased by 0.4 fold in the brains and tails, and RXRβ mRNA was increased by 5.9 fold in the tails after 96 h of exposure. MCT8 mRNA was increased by nearly 3 fold in the tails in 50 ng·L^-1 TBT treatment group and decreased by 3 fold or so in the brains in 50 ng·L^-1 TBT treatment group after 96 h of exposure. These results suggest that TBT can result in the changes of multiple mRNA expressions and show high tissue-specific differences. These mRNA are involved in the synthesis, transportations, transformations and actions, which indicate that TBT shows thyroid hormone disrupting effects. The changes of related mRNA expressions indicate that TBT might disrupt the thyroid hormone system of tadpoles by binding with retinoid X receptor. Therefore, biomarkers are not only cost-effective and sensitive endpoints in screening the thyroid disrupting chemicals but also useful in identifying the mode of action of contaminants.

Key words: Xenopus tropicalis, TBT, thyroid hormone response genes expressions