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(T/EH066) Relative estrogenic potencies of steroidal estrogens, and their interactive effects, in vivo, in fish. Thorpe, Karen1,2, Brighty, Geoff3, Cummings, Rob2, Hutchinson, Thomas2, Scholze, Martin4, Sumpter, John1, Tyler, Charles5, 1 2 3 4 5 ABSTRACT- The natural steroids, estradiol and estrone, and the synthetic steroid, ethinylestradiol, have been measured in waters receiving domestic effluents. Each of these steroids binds to the estrogen receptor and has been demonstrated to elicit estrogenic responses in a range of in vitro and in vivo assays. However, there are currently no chemical standards controlling the concentrations of these chemicals in the environment. To develop a standard for total steroidal estrogens, information is required on the relative potencies of each steroidal estrogen and their mixtures. The following study determined the relative estrogenic potencies of estradiol, estrone and ethinylestradiol and a mixture of estradiol and ethinylestradiol (equi-potent fixed ratio mixture) in a 14 day in vivo juvenile rainbow trout screening assay, using vitellogenin induction. After 14 days, plasma vitellogenin concentrations were measured and dose-response curves constructed for both the individual chemicals and the binary mixture. The observed effect for the mixture was compared with the predicted effect using the model of concentration addition. The results indicated that ethinylestradiol was approximately 25 times more potent and estrone 2.5 times less potent than estradiol in inducing vitellogenin. The binary mixture of estradiol and ethinylestradiol acted in an additive manner. These results suggest that the model of concentration addition could be used to develop an environmental quality standard for natural and synthetic steroids present in the environment. Key words: estrogen, mixture |
