[DNA alkylation and repair in female rats subjected to methylnitrosourea exposure at different ages].

Three- and fourteen-month old female rats received a single intravenous injection of 50 mg/kg 14C-methylnitrosourea. Peculiarities of DNA purines alkylation and repair in different organs were studied. The difference in initial methylpurine levels between the two groups appeared insignificant and did not correlate with the rate of tumor frequency registered in chronic experiments using the same mode of treatment. In young animals, the rate of O6-methylguanine repair in all tissues tested equaled or exceeded that in older ones. It is inferred that the rate and site of tumor development are influenced by alkylation level and rates of repair and proliferation in target tissues during treatment.