Thyroid endocrine disruption of acetochlor on zebrafish (Danio rerio) larvae

The herbicide acetochlor is widely used and detected in the environment and biota, and has been suspected to disrupt the thyroid endocrine system, but underlying mechanisms have not yet been clarified. In the present study, zebrafish larvae (7days post-fertilization) were exposed to a series concentration of acetochlor (0, 1, 3, 10, 30, 100 and 300 mu gl(-1)) within a 14-day window until 21days post-fertilization. Thyroid hormones and mRNA expression profiles of genes involved in the hypothalamic-pituitary-thyroid (HPT) axis were analyzed. Exposure to the positive control, 3,5,3-triiodothyronine (T-3), altered the mRNA expression, suggesting that the HPT axis in the critical window of zebrafish responded to chemical exposure and could be used to evaluate the effects of chemicals on the thyroid endocrine system. The mRNA expressions of genes involved in thyroid hormone synthesis (tsh, slc5a5 and tpo) were upregulated significantly with acetochlor treatment, which might be responsible for the increased thyroxine concentrations. The downregulation of genes related to thyroid hormone metabolism (dio1 and ugt1ab) and transport (ttr) in zebrafish larvae exposed to acetochlor might further explain the increased thyroxine levels and decreased T-3 levels. The mRNA expression of the thyroid hormone receptor (tr) was also upregulated upon acetochlor exposure. Results suggested that acetochlor altered mRNA expression of the HPT axis-related genes and changed the whole body thyroid hormone levels in zebrafish larvae. It demonstrated that acetochlor could cause endocrine disruption of the thyroid system by simulating the biological activity of T-3. Copyright (c) 2015 John Wiley & Sons, Ltd. Herbicide acetochlor has been suspected to disturb the thyroid endocrine system, but the underlying mechanisms have not yet been clarified. The present study suggested that zebrafish larvae in the time window could be used as a model for assessment of the thyroid endocrine disruption effects of pesticides. Acetochlor altered the mRNA expression of the hypothalamic-pituitary-thyroid axis-related genes and changed whole body thyroid hormone levels in zebrafish larvae, causing endocrine disruption of the thyroid system by simulating the biological activity of 3,5,3-triiodothyronine.