Thyroid endocrine disruption in zebrafish larvae following exposure to hexaconazole and tebuconazole

The widely used triazole fungicides have the potential to disrupt endocrine system, but little is known of such effects or underlying mechanisms of hexaconazole (HEX) and tebuconazole (TEB) in fish. In the present study, zebrafish (Danio redo) embryos were exposed to various concentrations of HEX (0.625, 1.25 and 2.5 mg/L) and TEB (1, 2 and 4 mg/L) from fertilization to 120 h. post-fertilization (hpf). The whole body content of thyroid hormone and transcription of genes in the hypothalamic-pituitary-thyroid (HPT) axis were analyzed. The results showed that thyroxine (T4) levels were significantly decreased, while triiodothyronine (T3) concentrations were significantly increased after exposure to HEX and TEB, indicating thyroid endocrine disruption. Exposure to HEX significantly induced the transcription of all the measured genes (i.e., corticotrophin-releasing hormone (CRH), thyroid-stimulating hormone (TSH beta), sodium/iodide symporter (NIS), transthyretin (TTR), uridine diphosphate glucuronosyltransferase (UGTlab), thyronine deiodinase (Dio1 and Dio2), thyroid hormone receptors (TR alpha and TR beta)) in the HPT axis, but did not affect the transcription of thyroglobulin (TG). However, TEE exposure resulted in the upregulation of all the measured genes, excepting that TG, Dio1 and TRa had not changed significantly. The overall results indicated that exposure to HEX and TEB could alter thyroid hormone levels as well as gene transcription in the HPT axis in zebrafish larvae. (C) 2013 The Authors. Published by Elsevier B.V. All rights reserved.