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To study the selective organospecific carcinogenesis by the specific chemical carcinogens, the breast cancer induction model by oral administration of 7, 12-dimethylbenzanthracene (DMBA) or by intravenous injection of N-methylni-trosourea (NMU) on female rats was analyzed. In the present experiment, we compared the effexts of ages on the chemical mammary carcinogenesis by studying the metabolic system of the carcinogenic activation, detoxification or DNA damage and repair. The breast tumor incidence was significantly higher in the young rats of 50 days old than in those of one year old rats. As an index of organospecific DNA damage or repair, the in vivo covalent binding index(CBI) of the specific organs by the specific chemical carcinogens was monitored. And for the analysis of carcinogenic activation, the quantity of cytochrome P450`s was determined with the respective type-specific monoclonal antibody, while the detoxication capacity was deduced by the activity monitoring of glutathione S-transferase (GST) and peroxidase. The skin tissues of the mammary region had the highest CBI with both of DMBA and NMU at 50 days of age. And there were contrasting differences in the contents of carcinogenic activation and detoxication system: that is, the content of T.C.D.D.-inducible cytochrome P450 was high, while the activities of GST and peroxidase was low in the mammary skin tissues at tumor prevalent age. These results led us to conclude that the molecular organospecific carcinogenesis, as illustrated with mammary carcinoge-nesis by DMBA and NMU, is operated probably through the differential capacity of the target tissues in the high carcinogenic activation, low detoxication and the low DNA repair function.
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