Invitro and in vivo estrogenic effects of 17α-estradiol in medaka (Oryziaslatipes)

17α-Estradiol (17α-E2), the stereoisomer of 17β-estradiol (17β-E2), is considered a weak estrogen in mammals. However, little is known about its estrogenic potency in teleost fish, even though 17α-E2 has been frequently detected in aquatic environment. To investigate the estrogenic activity of 17α-E2, an in vitro assay based on the ligand-dependent interaction between medaka estrogen receptor alpha (med-ERα) and coactivator was conducted. Japanese medaka (Oryziaslatipes) were exposed to 1, 10, 100, 1000 and 10 000 ng L−1 17α-E2 (actual concentrations of 1.91, 12.81, 96.24, 1045.15, and 9320.81 ng L−1, respectively) for 3 weeks, and expression for vitellogenins (VTG-I), Choriogenin H (CHG-H) and estrogen receptor α (ERα) mRNA in the livers was analyzed by quantitative real-time RT-PCR (Q-RT-PCR). The in vitro study showed that the EC50 of 17α-E2 was 114.10 nM, which was 30 times less potent than that of 17β-E2 (3.80 nM). Dose-dependent induction of gene expression of VTG-I, CHG-H and ERα were observed. The benchmark dose (BMD) values for VTG-I, CHG-H and ERα were 44.16 ng L−1, 15.25 ng L−1 and 66.03 ng L−1, which were about 11-, 17- and 14-times less potent than that of 17β-E2, respectively. Comparing this study with those reported previously in mammals, it is suggested that fish species may be more susceptive to 17α-E2 than mammals.