Sex differences in cytochrome P4501A induction by environmental exposure and β-naphthoflavone in liver and extrahepatic organs of recrudescent winter flounder

The differences between male and female winter flounder (Pseudopleuronectes americanus) in cytochrome P4501A induction caused by environmental and experimental exposure were studied. Prespawning male and female winter flounder were collected near Cape Ann, MA, USA, a site downstream of the Merrimack River plumes, which contain various agricultural and industrial effluents. One group of these fish was given βNF (20 mg/kg i.p.) and the other was analyzed as such. The catalytic activity measurements were run along with Western blotting for CYP1A quantitation. Immunohistochemical detection of the isoenzyme was used for further characterization of the differences in various tissues and cell types. The results obtained indicated that hormonal factors (presumably estradiol) suppress CYP1A induction in liver and some extrahepatic organs of females. Furthermore, the results showing high CYP1A content in liver but not in other organs of male fish from the environment indicate differences in the response of target tissues such as liver and kidney. Whether these involve differences in the half-lives of inducers or the half-life of CYP1A in liver and other tissues remains to be determined. Experimental βNF induction clearly altered the induction pattern seen in fish.