It is well known that a number ofcytochrome P450
(CYP or P450) subfamilies participate in steroid me- tabolism in fish (e.g. CYP2K and CYP3A; Stegeman and Hahn, 1994). In vitro and in vivo studies with mammals have also demonstrated a role ofAhR- regulated inducible CYP enzymes in E2 metabolism. For example, it was reported recently that both E2 and NP inhibited BNF-induced microsomal EROD activity in rat and fish (Lee et a!., 1996; Arukwe et a!.,
1997b). Elsewhere, TCDD, a potent CYP1A-inducer, has been shown to increase the hydroxylation of E2 at
2- and 16a-positions in human breast cancer cells
(Gierthy et a!., 1988). Hydroxylation ofE2 was also reported using purified rat CYP1A2 enzymes (Spink
et a!., 1990).