Induction of the hepatic microsomal and nuclear cytochrome P-450 system by hexachlorobenzene, pentachlorophenol and...

The application of hexachlorobenzene (HCB), pentachlorophenol (PCP) and 2,4,5-trichlorophenol (TCP) to female rats led to an induction of both the microsomal and the nuclear cytochrome P-450 system in the liver. The increase of th mixed-function hydroxylase activities examined (7-ethoxycoumarin deethylase, 7-ethoxyresorufin deethylase, NADPH-dependent cytochrome c reductase, aminopyrine demethylase, benzpyrene hydroxylase) did not correlate strictly with the cytochrome P-450 content. Depending on the inducers and the substrates used, the content and the activity of the cytochrome P-450 were essentially smaller in the nuclei than in the microsomes. It was striking that in the nuclei those activities (benzpyrene hydroxylase, 7-ethoxyresorufin deethylase, 7-ethoxycoumarin deethylase) were preferably induced which can be attributed to the methyl-cholanthrene-induced form of the cytochrome P-450 (cytochrome P-448). These results suggest, also in the light of findings of other authors, the induction of different species of cytochrome P-450 in the nuclei and microsomes.