Immunocytochemical localization of DNA adducts in rat tissues following treatment with N-nitrosomethylbenzylamine.

Immunocytochemical visualization of O6-methylguanosine (meGua) and 7-meGua shows that DNA methylation by N-nitrosomethylbenzylamine(NMBzA) occurs not only in the target organs for tumour induction by this nitrosamine, the oesophagus and (occasionally) the tongue, but also in other tissues (liver, lung, trachea, tracheal glands and nasal cavity) for which no tumour induction by NMBzA has been reported. Thus, the organotropic carcinogenic action of NMBzA cannot be exclusively ascribed to differences in levels of DNA methylation. Additional determinants of the cancer risk in extra-oesophageal tissues could be the small size of the NMBzA-activating target cell population and a low proliferative activity.