Dietary and other factors affecting nitrosomethylurea (NMU) formation in the rat stomach

Nitrosomethylurea (NMU) formation was measured radioactively in the stomach contents of rats fed 3H-methylurea and sodium nitrite, mostly in semi-synthetic diets. When methylurea and sodium nitrite were added to various diets, the NMU concentration, averaged over 1-4 hours after the food was presented, was 4.6 micrograms/kg stomach contents for low-protein, 2.7 for control semi-synthetic, 2.4 for high-fat, 1.26 for bran, 1.24 for high-protein and 0.54 for the commercial diet. With the low-protein diet, the amount of NMU after 1 hour was 36.6 micrograms, corresponding to 5.3% conversion of methylurea. The decrease in yield as protein content increased was attributed to buffering action and competition for nitrite by the protein, as well as to the effects of the latter on consistency. It may also be correlated with the observation that human gastric cancer is associated with high-starch low-protein diets. Nitrite in diet was more effective in producing NMU than the same nitrite concentration in drinking water, except with sodium nitrite concentrations less than or equal to 0.5 g/kg vehicle, where the position was reversed. Sodium ascorbate added to a semi-synthetic diet at a level of 2.9 g/kg inhibited NMU production by 50%.