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2L - Immunotoxicity - genotoxicity - ED (WEP/111) Effects of the antithyroid agent propylthiouracil in zebrafish (Danio rerio). van der Ven, Leo1, van den Brandhof, Evert-Jan2, Vos, José2, Power, Deborah3, Wester, Piet1, 1 RIVM, Lab. for Pathology and Immunobiology, Bilthoven, the Netherlands2 RIVM, Lab. of Ecotoxicology, Bilthoven, the Netherlands3 Universidade do Algarve, Faro, Portugal ABSTRACT- Some high production volume pollutants of the aquatic environment, such as PCBs or other organochlorine chemicals and polyhalogenated aromatic hydrocarbons, may disrupt the thyroid hormone system. In a partial life cycle assay with zebrafish, the effects of the reference compound propylthiouracil (PTU, 1, 10 and 100 mg/L) on reproduction, growth and development, as well as on histopathology of some target tissues were studied and compared to plasma thyroid hormone levels. PTU induced a concentration dependent increase of egg production, but had no effect on fertilisation rate or hatching. Lethal dysmorphogenesis was found in 8.1% of 4 dph larvae after parental exposure at the highest PTU level tested, and there was a dose-dependent decrease in body length and weight at 42 dph. At this time, there was also a concentration dependent decreased scale thickness, suggesting inhibited metamorphosis. PTU also induced activation of the thyroid follicles in a concentration dependent way, hyperaemia in the thyroid area in juveniles, and depletion of liver glycogen. Effects in adults were associated with decreased circulating levels of the thyroid hormones T3 and T4. These observations suggest that in these aquatic organisms, the most serious effect of disruption of the thyroid hormone system is an impairment of normal development. In the low and mid PTU concentration range used in this protocol, the impact of this effect seems, however, limited. The zebrafish model may assist in the identification of thyroid hormone disrupting activity in water samples, and also in the interpretation of (histo-)morphological observations in free-ranging fish species. Illustrations of these effects are available in the toxicological pathology atlas of zebrafish at http://arch.rivm.nl/milieu/rivmzfatlas/fishtoxpat/fishtoxpat/index.htm. Key words: thyroid hormones, endocrine disruption, zebrafish (danio rerio), histology |
