Estrogen enhances induction of cytochrome P-4501A1 by 2,3,7,8-tetrachlorodibenzo-p-dioxin in lives of female Long-Evans rats

A human carcinogen, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) induces live r tumors in female rats. In this study, we examined the effects of estrogen on an arylhy-drocarbon receptor (AhR)-responsible protein, CYP1A1 expressi on induced by TCDD in female rat livers. The induction of CYP1A1 by a dose of 300 ng TCDD/kg and its resultant enzymatic activity were significantly e nhanced by 5 mu g 17 beta-estradiol/kg body weight treatment to both intact and ovariectomized rats. Immunoblot analysis showed a increase in nuclear AhR due to estrogen, TCDD or both, suggesting that estrogen is involved in the activation of CYP1A1 gene after the formation of AhR-TCDD complex.