Effect of administration of the carcinogen dimethylnitrosamine on urinary 7-methylguanine.

1. Evidence is presented for the excretion of 7-methylguanine in normal rat urine at a rate of approx. 65mug./day. Experiments with animals in which the nucleic acids had been prelabelled by treatment of the neonatal rats with [(14)C]-formate gave evidence that the methylated base originated in the nucleic acids of the rat. 2. Injection of [(14)C]dimethylnitrosamine leads to an increased excretion of 7-methylguanine, and the base becomes labelled in the methyl group. The disappearance of labelled 7-methylguanine formed in nucleic acids of rats treated with the carcinogen therefore does not take place by an N-demethylation reaction, but by liberation of the intact methylated base.