Decrease in the activity of hepatic microsomal drug-metabolizing enzymes in tumor-bearing nude mice.

The activities of hepatic microsomal drug-metabolizing enzymes in nude mice (BALB/c-nu/nu) bearing tumors of human or nude mouse origin were studied. The content of cytochrome P-450 and the activities of cyclophosphamide oxidase, benzo[a]pyrene hydroxylase, aniline hydroxylase and benzphetamine N-demethylase were markedly decreased in tumor-bearing nude mice in accordance with previous observations in tumor-bearing rats and mice. These results indicate that decreases in the activities of hepatic microsomal drug-metabolizing enzymes are not the consequence of an immunoreactive process or cachexia.