Transient structural change in hepatic DNA of rats chronically exposed to dimethylnitrosamine.

Structural analysis by chromatography on benzoylated-DEAE-cellulose (BD-cellulose) has been made of hepatic DNA from rats treated for up to 21 weeks with dimethylnitrosamine (DMN). The carcinogen (1 mg/kg body wt) was administered on a daily basis by intraperitoneal injection. By comparison with preparations from saline-treated controls, the proportion of DNA retained by benzoylated-DEAE-cellulose in the presence of 1.0 M NaCl was increased by administration of the carcinogen. Variation in the result, dependent upon the time after the final dose, suggested a complex relationship between structural damage to DNA and duration of treatment. Structural damage was confirmed by S1 nuclease digestion. The observations imply that in the course of chronic administration, increasing time is required to complete DNA repair processes operative in rat liver.