Effect of chronic administration of dimethylnitrosamine on the excision of 06-methylguanine from rat liver DNA

Summary Rats were exposed chronically to unlabelled N , N -dimethylnitrosamine (25 ppm in the drinking water) then given a single dose of N -[ 3 H]methyl- N -nitrosourea (10 mg/kg body weight). The rates of loss of tritium-labeled 7-methylguanine, 0 6 -methylguanine and 3-methyladenine from the liver DNA in control and dimethylnitrosamine-treated rats were found not to be significantly different. Thus, under the conditions used, inhibition of the 0 6 -methylguanine excision repair system does not seem to be a factor in the induction of liver tumours by chronic DMN application.