EXPOSURE OF KILLIFISH TO BENZO[A]PYRENE - COMPARATIVE METABOLISM, DNAADDUCT FORMATION AND ARYL-HYDROCARBON (AH) RECEPTOR AGONIST ACTIVITIES

Benzo[a]pyrene (BaP) elicited a dose-response induction of hepatic CYP 1A1 gene expression in killifish characterized by increased CYP1A1 mRN A levels, ethoxyresorufin O-deethylase (EROD) and aryl hydrocarbon hyd roxylase (AHH) activities. There were marked differences in the maxima lly-induced EROD (1529 pmol mg(-1) min(-1)) and AHH (377 pmol mg(-1) m in(-1)) activities and these differences were observed at all time poi nts and at concentrations of BaP from 1 to 50 mg/kg, Treatment of kill ifish with BaP did not significantly affect binding of [I-125]epiderma l growth factor (EGF) to hepatic plasma membranes containing the EGF r eceptor. There was a dose-dependent increase in formation of DNA adduc ts in killifish treated with 1-50 mg/kg of BaP. Two-dimensional thin-l ayer chromatographic analysis of the [P-32] labeled adducted nucleotid es revealed one major spot. In a time course study over a period of 2- 14 days, the relative DNA adduct levels in fish treated with 5 mg/kg B aP were constant. The most sensitive indicator of exposure to BaP was the dose-dependent formation of biliary metabolites in which there was a > 40-fold increase (compared to untreated animals) in fluorescent m etabolites formed at the lowest dose of BaP (1 mg/kg) used in this stu dy. Killifish expressed relatively high levels (203 fmol/mg) of the nu clear aryl hydrocarbon (Ah) receptor which was isolated from nuclear e xtracts of fish treated with [H-3]-2,3,7,8-tetrachlorodibenzo-p-dioxin . The nuclear Ah receptor complex sedimented at 6.0 S which was simila r to that observed in other animal species. Based on their CYP1A1 indu ction response to BaP and Ah receptor levels, the results of this stud y indicate that killifish are highly Ah-responsive.