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Effects of waterborne exposure of octylphenol and oestrogen on pregnant viviparous eelpout (Zoarces viviparus) and her embryos in ovario
1 Institute of Biology, University of Southern Denmark, Odense,
Denmark
2 Lab. of Pathology and Immunobiology, National Institute of Public Health
and the Environment (RIVM), Bilthoven, The Netherlands
* Author for correspondence (e-mail: tinac{at}biology.sdu.dk)
Accepted 16 September 2002
Exposure to oestrogenic chemicals (xeno-oestrogens) may have severe effects on embryonic development. The present study investigates whether the oestrogenic endocrine disruptor 4-tert-octylphenol (4-tOP) or 17ß-oestradiol (E2) is accumulated in the viviparous fish the eelpout (Zoarces viviparus) and transferred to the embryos in ovario and subsequently affects embryonic development, including gonadal differentiation. Pregnant eelpouts were exposed to nominal concentrations of 25 µgl-1 or 100 µgl-1 4-tOP (OP25 or OP100, respectively) or 0.5 µgl-1 E2 in water. During 4-tOP exposure, the compound accumulated in both plasma and ovarian fluid in a concentration-dependent manner. In the mother fish, the oestrogenic biomarkers, vitellogenin (Vtg) in plasma, Vtg mRNA in liver and oestrogen-binding activity in liver, were all induced by 4-tOP (and by E2) at an actual concentration of 14 µgl-1. E2 and 4-tOP were examined for their potency to disturb the maternal—foetal trophic relationship by disturbing the physiology of the ovary and by changing the distribution of essential nutrients normally transported to embryos during pregnancy. After exposure to E2 or 4-tOP, calcium was depleted from the ovarian fluid and the level of free amino acids available in maternal plasma was decreased. A marked overall effect on ovarian components, including the ovarian sac, ovarian fluid and embryonic mass, was evident. Embryonic growth was significantly decreased, which might in part be attributed to disturbances of the maternal—foetal trophic relationship. Marked inductions of Vtg mRNA and Vtg protein, determined by RT-PCR and immunohistochemistry, respectively, were found in embryos from the OP100 group — the only group to show considerable accumulation of an oestrogenic compound in the ovarian fluid. A different pattern of gonadal development was found in embryos from the OP100 group compared with embryos from the control, OP25 or E2 groups, in which approximately 50% had normal ovaries and 50% had normal presmptive male gonads. In the OP100 group, 46% had normal ovaries but, in contrast to controls, only 22% had normal presumptive male gonads, whereas the remaining 32% had abnormal male gonads with structures resembling the endo-ovarian cavity of a female gonad. As oestrogen receptor (ER) expression was detected by in situ hybridisation in early differentiating gonads, these effects could be mediated by direct interaction of the xeno-oestrogens with gonadal ER. In conclusion, this study indicates that the xeno-oestrogen 4-tOP can be transferred from the water via the mother fish to the ovarian fluid and can subsequently disturb the maternal—foetal trophic relationship and cause severe effects on embryonic development, including gonadal differentiation in ovario.
Key words: development, embryo, endocrine disrupter, oestrogen, fish, gonad, histology, maternal—foetal relationship, alkylphenol, oestrogen receptor, sex differentiation, vitellogenin mRNA, immunohistochemistry, xeno-oestrogen, viviparous, Zoarces viviparus, eelpout
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