CY1P1-, CYP2B- AND CYP3A-LIKE PROTEINS IN RAINBOW-TROUT (ONCORHYNCHUS-MYKISS) LIVER - CYP1A1-SPECIFIC DOWN-REGULATION AFTER PROLONGED EXPOSURE TO PCB

Induction of cytochrome P450 1A (CYP1A) has been widely employed as a biomarker for exposure to halogenated aromatic hydrocarbons, such as c o-planar PCB, in the aquatic environment. Recently, however, non-respo nsiveness to PCB has been reported in fish collected from heavily PCB- contaminated sites in North America and Europe. In a recent study, we investigated the CYP1A1 system in juvenile rainbow trout (Oncorhynchus mykiss) after an initial intra peritoneal injection of either carrier vehicle, 3-methylcholanthrene (3-MC) or a PCB mixture (Clophen A50) i n a 20-week laboratory experiment. Furthermore, we showed that prolong ed exposure to PCB seems to impair the inducibility of the CYP1A1 syst em in rainbow trout liver (Celander & Forlin, 1995). In the present st udy, immunoblot analyses confirms that this apparent down-regulation w as specific to CYP1A1, while levels of CYP2B- and CYP3A-like proteins remained mainly unchanged. Copyright (C) 1996 Elsevier Science Ltd.