Studies on the microsomal cytochrome P450s in the livers of carcinogen-resistant and sensitive rats during long-term administration of 3'-methyl-4-dimethylaminoazobenzene.

Time-course studies on the microsomal cytochrome P450s in the livers of carcinogen-resistant (DRH) and sensitive (Donryu) rats were carried out during a long-term administration of 3'-methyl-4-dimethylaminoazobenzene (3'-Me-DAB). Total contents of the microsomal cytochrome P450s were gradually reduced with time in the Donryu rat livers, while those in the DRH rats did not alter significantly under these conditions. The activities of several isoforms of cytochrome P450 (CYP1A1, CYP1A2, and CYP2E1) were determined separately during these experimental periods. However, we could not obtain satisfactory evidence which may explain the different susceptibility to chemical carcinogenic actions in the livers between DRH and Donryu rats. Lower total contents of cytochrome P450s in the Donryu rats during the later stage may be due to the hepatic injuries caused by long-term administration of 3'-Me-DAB.