Effects of polychlorinated biphenyls and environmental temperature on in vitro formation of benzo[ a]pyrene metabolites by liver of trout ( Salmo gairdneri)

Abstract

Rainbow trout ( Salmo gairdneri) held at 7° and 16° were given Aroclor 1254 (PCB) (10mg/kg body wt) via intraperitoneal injections. The binding of [ 3H]benzo[ a]pyrene (BaP) to deproteinized salmon sperm DNA was assayed (pmoles BaP equivalents per mg DNA per mg protein) using the post-mitochondrial supernatant (S 10) fractions from livers of fish at 24–168 hr after the PCB exposure. Liver enzymes from the untreated fish acclimated at 7° yielded an average binding value (0.37 ± 0.17) which was significantly greater (P < 0.05) than the value (0.07 ± 0.03) for untreated fish at 16°. Liver supernatant fractions from PCB-induced fish acclimated at 16° and sampled at 24–120 hr showed a substantial increase (P < 0.05) in the binding (average value 2.4 ± 1.8) compared to the value obtained with untreated fish at 16°. At 24, 48 and 120 hr after the PCB treatment of fish held at 7°, there was no significant increase in the binding value or extent of metabolism of BaP compared to that obtained with the untreated fish at 7°. However, at 168 hr, three of four fish at 7° responded to the PCB treatment with significantly (P < 0.05) increased binding values (3.3 ± 1.6). Chromatographic analyses of the ethyl acetate-soluble metabolites revealed that 3-hydroxy BaP and 7,8- and 9,10-dihydrodiols were the major metabolites; K-region metabolites were formed in trace amounts in untreated and PCB-treated fish at both temperatures. No marked qualitative differences were observed in metabolite profiles after the PCB treatment; however, overall metabolism of BaP and production of reactive metabolites by liver enzymes were considerably (P < 0.05) enhanced in the PCB-induced fish at both 7° and 16°.