[Effect of age on carcinogenesis in female rats induced by methyl (acetoxymethyl) nitrosamine].

A single intraperitoneal injection of methyl-acetoxymethyl-nitrosamine produced tumors in 85.7% of 3 month-old female rats and in 62.5% of 14 month-old ones matched by 26.5% in controls. Intestinal tumors developed most frequently. Also, tumors of the pituitary, thyroid, breast, uterus as well as leukemia were detected. Multiple intestinal tumors were more frequent in the young age group (1.43 and 1.00), tumor-free interval in older animals being 217 days longer. Studies on DNA alkylation and repair were carried out using intraperitoneal injections of 14C-methyl-acetoxymethyl-nitrosamine. Young animals showed higher levels of methylpurines in organ tissues other than those of small intestine 3 hrs after treatment. The rate of methylpurine excretion in young rats was higher, too. However, liver tissue of old rats showed a higher rate of O6-methylguanine repair than that in younger ones.