Characterization of a cytosolic estrogen receptor and its up-regulation by17 beta-estradiol and the xenoestrogen 4-tert-octylphenol in the liver of eelpout (Zoarces viviparus)

Estrogen binding activity was revealed in the cytosolic fraction of hepatic extracts from adult male and female eelpout (Zoarces viviparus). The bindi ng moiety was characterized by a single class of high affinity binding site s (K-d = 0.59 +/- 0.05 nM in males and 1.06 +/- 0.10 nM in females). The af finity was significantly higher in males. Binding sites were satiable and b inding 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 sp ecific to known estrogens but not to other tested steroids. The binding moi ety was able to bind to DNA-cellulose and was extractable by high salt conc entrations. A time-course study of estrogen binding activity in liver cytos ol and of vitellogenin (Vtg) in plasma, after intraperitoneal (i.p.) inject ions of 17 beta-estradiol (E-2) in male eelpout, was carried out. It was sh own that both are inducible by E-2. Estrogen binding activity was significa ntly elevated 48 h and Vtg 72 h after E-2 treatment. The binding moiety was hereafter designated as a cytosolic estrogen receptor (ER). The estrogenic ity of 4-tert-octylphenol (OP) was evaluated by measuring ER and Vtg after i.p. treatment. OF-treatment increased both receptor levels and Vtg concent rations in male fish, indicating that OP acts as an estrogen in male eelpou t. (C) 2000 Elsevier Science Inc. All rights reserved.