Estrogen receptor expression and vitellogenin synthesis induced in hepatocytes of male frogs Rana chensinensis exposed to bisphenol A

The effects of bisphenol A (BPA) on estrogen receptor (ER) and vitellogenin (VTG) in hepatocytes of male amphibians have attracted significant attention in recent years. Adult male frogs Rana chensinensis were exposed to different concentrations of 10^-7, 10^-6 and 10^-5 mol/L BPA consecutively for 10, 20, and 30 d, respectively. We used 10^-9, 10^-8 mol/L 17β-esradiol (E₂) as positive controls. The expressions of ER mRNA in the hepatocytes were detected by in situ hybridization, and ER and VTG protein were detected by immunohistochemistry. The results showed that positive effects of ER mRNA were detected in all BPA and E₂ treatment groups. Compared with the control group, the expression level of ER and VTG protein increased significantly in the hepatocytes of R. chensinensis. Both ER and VTG expression exhibited BPA dose-dependence for the same exposure time. For the same concentration of BPA treatment, VTG synthesis markedly increased with prolonged treatment, whereas the expression of ER did not significantly fluctuate. It is suggested that BPAcaused the synthesis of VTG by inducing ER up-regulation in the hepatocytes of male R. chensinensis, but its estrogenic activity was much lower than E₂.