The activities of microsomal enzymes were observed during perfusion of livers isolated from both normal and phenobarbital treated rats. The hydroxylation of aniline and the O-demethylation of p-nitroanisol did not decrease substantially (by 10 per cent only) in the 9000 g fraction prepared from livers perfused for 4 hr. N-demethylation of aminopyrine was reduced by 60 per cent in the same experimental conditions. A similar decrease of N-demethylation was also observed when livers were isolated from animals treated with phenobarbital. The content of cytochrome P-450 in the microsomes was stable during a 4-hr perfusion of isolated liver. The decrease of N-demethylation of aminopyrine could be partly restored by the simultaneous infusion of nicotinic acid, which is a precursor of NAD and NADP biosynthesis.
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