In the present study we investigated the effect of stress and cortisol on cytochrome P450 (CYP) expression in Arctic charr exposed to benzo[a]pyrene (BaP). Expression of hepatic CYP1A and CYP3A was monitored 8 d after a single oral dose of BaP (10 mg/kg fish) and compared to that in unexposed fish. During this period the fish were subjected to one of the following stress regimes: no stress, no stress and cortisol implantation, 10 min of daily handling and confinement stress, and confinement stress during the last 6 h before sampling. In BaP-exposed fish daily stress resulted in significantly lower (53%) CYP1A protein levels as compared to those in unstressed fish. For CYP1A catalytic activity (measured as 7-ethoxyresorufin-O-deethylase [EROD] activity), the suppressive response to stress was less pronounced. These results contrast to previous findings of a potentiation by corticosteroids on xenobiotic-dependent CYP1A induction in vitro in cultured fish hepatic cells. No effects of high cortisol levels or BaP were found on the steroid-metabolizing CYP3A enzyme levels. The lack of any alterations in the CYP3A protein level indicates that CYP3A expression is not inducible by cortisol in the Arctic charr under the conditions used here. The conclusion was made that short-term stress associated with sampling (i.e., 6 h of confinement stress before sampling) of wild charr does not compromise the EROD activity as a reliable biomarker.
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