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(T/FF217) Estrogenic effects of phthalates in fish: an example of multiple modes of action. Tollefsen, Knut-Erik1,2, Frydenlund, Jorid2, Meys, Joris2, Stenersen, Jørgen2, 1 2 ABSTRACT- Phthalates (phthalate esters), which is a group of industrial plasticizers found abundantly as contaminants in the aquatic environment, have been suspected of being estrogenic. Although the phthalates have displayed estrogenic properties in several in vitro bioassays, the in vivo estrogenic activity of these chemicals are largely unknown under environmentally realistic exposure conditions. In this study, the in vitro and in vivo estrogenic activity of n-butyl benzyl phthalate (BBP), di-(n-butyl) phthalate (DBP) and di-(2-ethylhexyl) phthalate (DEHP) was assessed using the estrogen receptor (ER)-mediated production of the yolk precursor protein vitellogenin (Vtg) and eggshell zona radiata (Zr) proteins as biomarkers for estrogenic effects in Atlantic salmon (Salmo salar). The result from the studies show that both BBP and DBP are acting as estrogenic agonists under in vitro exposure conditions, whereas only BBP was estrogenic under flow through exposure conditions. DEHP was not found to be estrogenic, neither in vitro nor in vivo. Although BBP and DBP was found to be weakly estrogenic or non-estrogenic in vivo, these chemicals were able to interact with the plasma sex steroid-binding proteins (SBP) and alter the production of the plasma SBP in low ug/l concentrations. The SBP are believed to be involved in the regulation of circulating endogenous sex steroids as well as cellular signal transduction to nuclear steroid receptors. In conjunction with the reported anti-androgenic properties of some phthalates, our findings suggest that these chemicals are able to modulate the endocrine system by multiple modes of action, which may work in concert to produce "estrogen-like" effects in fish. Key words: endocrine disrupters, vitellogenin, sex steroid-binding proteins, Atlantic salmon |
