Short-term effects of endocrine-disrupting chemicals on the expression of estrogen-responsive genes in male medaka (Oryzias latipes)

To evaluate the estrogenic activities of selected estrogenic compounds such as estradiol-17β (E2), nonylphenol (NP), 4-(1-adamantyl)phenol (AdP), bisphenol A (BPA), BPA metabolite 4-methyl-2,4-bis(4-hydroxyphenyl)pent-1-ene (MBP) and 4,4′-dihydroxy-α-methylstilbene (DHMS) in the shortest possible time, we investigated the expression of estrogen-responsive genes such as vitellogenin I, vitellogenin II and α-type estrogen receptor genes in the liver of male medaka (Oryzias latipes) using reverse transcription-polymerase chain reaction (RT-PCR) techniques. These estrogen-responsive genes responded rapidly to selected estrogenic compounds after 8 h exposure, and the expression of hepatic vitellogenin II and estrogen receptor α mRNA was found to be more responsive than that of vitellogenin I mRNA. As a result, the relative estrogenic potencies of tested chemicals descended in the order of E2 (100) > MBP (0.38) > AdP (0.25) > DHMS (0.05) > NP (0.02) > BPA (0.001). Moreover, this preliminary study indicates that AdP and DHMS should be considered as candidate estrogenic compounds with the potential to induce hepatic estrogen-responsive genes in male medaka. These results suggest that vitellogenin I, vitellogenin II and estrogen receptor α gene expression patterns alter in male medaka treated with selected estrogenic compounds, and that these genes may be useful molecular biomarkers for screening estrogenic endocrine-disrupting chemicals in the shortest possible time.