Induction of hepatic xenobiotic biotransformation enzymes in rainbow trout by β-naphthoflavone. Time-course studies

Abstract

1. 1. Hepatic microsomal cytochrome P-450 and b 5 contents, and ethoxyresorufin- O-deethylase (EROD), UDP glucuronyltransferase (UDPGT) and cytosolic glutathione transferase (GSHT) activities were maximally induced after various periods of time following a single i.p. injection of BNF (50 mg/kg) in rainbow trout. 2. 2. Cytochrome P-450 content and EROD and UDPGT activities were significantly elevated 3 days after treatment while GSHT activity did not reach significantly higher levels until 14 days had elapsed. 3. 3. NADPH cytorchome c reductase activity was not affected by the treatment. 4. 4. After 59 days, there was no significant differences between control and treated groups in cytochrome P-450 and b 5 contents, whereas GSHT activity, EROD and UDPGT activities were still significantly elevated. 5. 5. The second treatment with BNF resulted in an additional elevation of cytochrome P-450 content and EROD activity, but no effect on the induced cytochrome b 5 content and UDPGT activity, whereas it inhibited the induced GSHT activity. 6. 6. A single injection of a low dose of BNF (50 μg/kg) did not result in any apparent effects on the cytochrome P-450 and cytorchome b 5 contents whereas the activity of EROD was significantly elevated at 12, 24, 48 and 96 hr after treatment. 7. 7. In addition, ECOD activity was elevated 48 hr after treatment. At the send of the experiment (192 hr post-injection) no differences in enzyme activity were observed. 8. 8. The study demonstrates that BNF-induced xenobiotic biotransformation enzymes in fish return to basal levels after a recovery period.