Carcinogenicity of deuterium-labeled N-nitroso-N-methylcyclohexylamine in rats.

F344 rats were treated with both unlabeled N-nitroso-N-methylcyclohexylamine (NMC) and deuterium-labeled NMC (NMC-d3) in the methyl group. Both compounds were administered in the drinking water at concentrations of 50 and 12.5 mg/liter. The NMC-d3 was not less carcinogenic than the unlabeled NMC, which suggested that oxidation of the methyl group is not a rate-limiting step in the induction of esophageal tumors.