Nitrate as a precursor of the in-vivo formation of N-nitrosomorpholine in the stomach of guinea-pigs.

Reduction of nitrates to nitrites and formation of the carcinogen N-nitrosomorpholine (NMOR) was investigated in the stomach of guinea-pigs. A semisynthetic diet with nitrate plus morpholine was administered intragastrically after a 24-h fast; after treatment, the animals were killed and stomach nitrite contents were determined 6, 12, 18, 24 and 30 min after the treatment using a colorimetric method. NMOR content was determined 18 min after treatment with nitrate plus morpholine using gas chromatography-thermal energy analysis. Reduction of nitrates to nitrites in the stomach was observed that was sufficient to synthesize NMOR in guinea-pigs under the conditions of this experiment.