INDUCTION OF CYTOCHROME P450-ASSOCIATED MONOOXYGENASES IN NORTHERN LEOPARD FROGS, RANA-PIPIENS, BY 3,3',4,4',5-PENTACHLOROBIPHENYL

Northern leopard frogs (Rana pipiens) were injected intraperitoneally either with a solution of polychlorinated biphenyl (PCB) 126 in corn o il at a concentration of 0.2, 0.7, 2.3, or 7.8 mg/kg body weight or wi th corn oil alone. Appropriate assay conditions with hepatic microsome s were determined for four cytochrome P450-associated monooxygenases: ethoxyresorufin-O-dealkylase (EROD), methoxy-ROD (MROD), benzyloxy-ROD (BROD), and pentoxy-ROD (PROD). One week after PCB administration. th e specific activities of EROD, MROD, BROD, and PROD were not elevated at doses less than or equal to 0.7 mg/kg (p > 0.05) but were significa ntly increased at doses greater than or equal to 2.3 mg/kg compared to the control groups (p < 0.05). The increased activities of these four enzymes were 3 to 6.4 times those in the control groups. The increase d activities were maintained for at least 4 weeks. Because of a lack o f induction at low doses of PCB 126, which were still relatively high compared to currently known environmental concentrations, we suspect t hat EROD, MROD, BROD, and PROD activities are not sensitive biomarkers for coplanar PCB exposure in leopard frogs.