Study of the carcinogenicity of large doses of dimethylnitramine, N-nitroso-L-proline, and sodium nitrite administered in drinking water to rats.

Large doses of dimethylnitramine (DMNM), N-nitroso-L-proline (NPRO), and sodium nitrite were administered in the drinking water to MRC Wistar rats for at least 1 year, and the rats were maintained for life. DMNM (total dose, 20 g/kg) produced liver tumors in 25 (69%) of the 36 rats and nasal cavity tumors in 9 (25%) of the rats. NPRO (total dose, 36 g/kg) induced no tumors in 37 treated rats. In the group receiving NaNO2 (3.0 g/liter drinking water; total dose, 63 g/kg), 8 (18%) of 45 rats had forestomach squamous papillomas. The tumor incidence in the NaNO2-treated group was significantly greater than that of 2% in a control group started 11 months earlier, which suggested that the NaNO2 was tumorigenic in this experiment.