Characterization of a cytosolic estrogen receptor and its up-regulation by 17β-estradiol and the xenoestrogen 4 -tert-octylphenol in the liver of eelpout ( Zoarces viviparus)

Abstract

Estrogen binding activity was revealed in the cytosolic fraction of hepatic extracts from adult male and female eelpout ( Zoarces viviparus). The binding moiety was characterized by a single class of high affinity binding sites ( K d=0.59±0.05 nM in males and 1.06±0.10 nM in females). The affinity was significantly higher in males. Binding sites were satiable and binding capacity was significantly elevated in vitellogenic females (2.92±0.28 pmol/g) compared to males (1.67±0.11 pmol/g). The binding was specific to known estrogens but not to other tested steroids. The binding moiety was able to bind to DNA–cellulose and was extractable by high salt concentrations. A time-course study of estrogen binding activity in liver cytosol and of vitellogenin (Vtg) in plasma, after intraperitoneal (i.p.) injections of 17β-estradiol (E 2) in male eelpout, was carried out. It was shown that both are inducible by E 2. Estrogen binding activity was significantly elevated 48 h and Vtg 72 h after E 2 treatment. The binding moiety was hereafter designated as a cytosolic estrogen receptor (ER). The estrogenicity of 4- tert-octylphenol (OP) was evaluated by measuring ER and Vtg after i.p. treatment. OP-treatment increased both receptor levels and Vtg concentrations in male fish, indicating that OP acts as an estrogen in male eelpout.