[Relationship between tissue mitotic activity, animal age and defects in the secondary structure of DNA].

The content of defects of the secondary structure of DNA native and gamma-irradiated preparations from the intestinal mucosa and liver of adult (6-8 months) and old (24-26 months) rats was studied by the kinetic formaldehyde method. The content of the native DNA secondary structure defects does not depend on the animal and tissue mitotic activity. After gamma-irradiation in vitro (60Co, 550 R/min, 3 and 6 krad) of intestinal mucosa DNA solutions (tissues with a high mitotic activity) the content of the DNA defects is higher in old animals than in young ones. The injuring effect of gamma-rays is more pronounced in experiments with intestinal mucosa DNA than with liver DNA (tissue with a low mitotic activity). In liver DNA the content of the defects caused by gamma-rays does not depend on the animal age.