Induction of xenobiotic metabolism in rats by brominated diphenyl ethers administered for 90 days.

The administration of doses as low as 0.78 mu mol/kg/day p.o. for 90 dys of the commercial fire retardants pentabromodiphenyl ehter and octabromodiphenyl ether to rats resulted in increased O-ethyl O-p-nitrophenyl phenylphosphonothioate (EPN) detoxification and p-nitroanisole demethylation. This dose of pentabromodiphenyl ehter and higher doses of octabromodiphenyl ether also increased cytochrome P-450 and NADPH cytochrome c reductase. Measurements made at 30 and 60 days after the last dose showed that these indicators of induced xenobiotic metabolism return to control levels slowly. The results demonstrate that these inducers are not only potent but that their effects may be long-lasting.