CYTOCHROME P450E (P450IA) INDUCTION AND INHIBITION IN WINTER FLOUNDER BY 3,3',4,4'-TETRACHLOROBIPHENYL - COMPARISON OF RESPONSE IN FISH FROM GEORGES BANK AND NARRAGANSETT BAY

Induction of liver microsomal cytochrome P450 by 3,3',4,4'-tetrachlorobiphenyl (TCB) was evaluated in winter flounder from two different sites, one offshore (Georges Bank) and one coastal (Narrow River, Narragansett, Rhode Island). Immunoblot analysis of liver microsomes with monoclonal antibody 1-12-3 to scup P450E (P450IA1) revealed P450IA protein content of 0.01 nmol/mg in Georges Bank fish that were not treated with TCB. By comparison, untreated Narrow River fish had an 80-fold greater content of immunodetected P450IA protein, indicating a strong environmental induction in these fish. In Georges Bank fish the total (spectrophotometrically measured) microsomal P450 content and the content of P450IA protein were induced progressively by intraperitoneal doses of TCB ranging from 0.1 to 10.0 mg/kg. Ethoxyresorufin-O-deethylase (EROD) specific activity (activity per mg protein) was also progressively induced, but the catalytic efficiency or turnover number (i.e., activity/nmol P450IA) was less in fish given the greater doses of TCB. In Narrow River fish TCB treatment resulted in no significant change (at P less-than-or-equal-to 0.05) in total microsomal P450 content or in P450IA protein content, although they tended to be less (total P450) or greater (P450IA) in fish given the greater doses. The EROD activity per mg protein was less in Narrow River fish given greater TCB doses than it was in control fish. EROD activities per nmol of P450IA protein in control Narrow River fish were less than those in any treatment group of Georges Bank fish and tended to diminish even further with TCB treatment. The results show that 3,3',4,4'-TCB induces P450IA in winter flounder and that TCB acts in vivo to inhibit the activity of P450IA enzyme by mechanisms not yet known. The lower catalytic efficiency of P450IA enzyme in Narrow River fish than in Georges Bank fish indicates that P450IA inhibition, whether caused by TCB or some other agent, does occur in the environment. The data also indicate that prior condition, including existing environmental induction, can strongly influence the responses of P450IA protein to additional chlorobiphenyl exposure.