INDUCTION OF CYTOCHROME P450-1A1 AND CONJUGATING ENZYMES IN RAINBOW-TROUT (ONCORHYNCHUS-MYKISS) LIVER - A TIME-COURSE STUDY

1. The effects of i.p. injections of isosafrole (ISF) or beta-naphthoflavone (beta-NF) on the cytochrome P450 (CYP) 1A1 system and conjugating enzymes were investigated in livers from juvenile rainbow trout in a time course study employing catalytic, immunochemical and cDNA probes. 2. Beta-NF treatment resulted in a rapid rise in CYP1A1 mRNA followed by accumulation of P450 1A1 protein and P450 1A1 mediated enzyme activity measured as ethoxyresorufin-0-deethylase (EROD) activity. 3. ISF treatment resulted in a comparatively weak induction of CYP1A1 mRNA and P450 1A1 protein levels whilst EROD activity was markedly induced; thus when expressed on the basis of immunoquantified P450 1A1 protein, the specific EROD activity was significantly higher in ISF than beta-NF treated fish. 4. In vitro inhibition studies revealed that ISF inhibited EROD activity to a far lesser extent than beta-NF. 5. Conjugation enzymes represented by phenol UDP-glucuronosyltransferase and glutathione S-transferase (GST) activities, were induced by beta-NF, whereas ISF treatment had no effect on these enzyme activities. 6. Immunoblotting using antibodies raised against rat GST7-7 showed that a Pi class trout GST enzyme was induced by beta-NF treatment.