The effect of in vivo co-exposure to estrone and AhR-ligands on estrogenic effect to vitellogenin production and EROD activity

We evaluated the effect of combination chemical exposure on estrogenic activity, in vivo using Japanese medaka (Oryzias latipes) during co-exposure to estrone (E1) and β-naphthoflavone (βNF) or α-naphthoflavone (αNF). We used E1 because which is one of the major estrogenic substances in the environment, and βNF or αNF are both AhR-ligands and usually used as a model substance of common environmental pollutants such as PAHs from physiological response standpoint. The results of present study demonstrate that both βNF and αNF inhibit the E1-induced production of plasma VTG in a concentration-dependent manner. These results indicate that estrogenic activity is suppressed by AhR-ligands in aquatic environment. At the same time, significant increase of EROD was observed in groups of βNF co-exposed with E1, conversely no significant alteration of EROD was observed in groups of αNF co-exposed with E1. Therefore, we conclude that the inhibition of VTG synthesis effect was not directly related to EROD.