Instability of N-nitroso compounds in gastric juice and preliminary results from analyses of fresh samples by using an improved analytical method.

Using an improved method for determination of total N-nitroso compounds (NOC), we examined the stability of those compounds in fresh gastric juice samples during storage and the effects of the addition of 2% sulphamic acid on NOC concentration in 212 samples. The NOC levels in fresh samples decreased very rapidly at -20 degrees C, especially during the first 24 hours of storage (P < 0.01), and nitrite concentration also showed a decreasing trend during storage. The addition of sulphamic acid significantly reduced NOC levels from 1.97 +/- 0.21 to 1.10 +/- 0.12 mumol/l (mean +/- SE, P < 0.01), especially in samples of initially high pH. However, in some individual samples (16.5%) the NOC levels actually increased by 14.1% (P < 0.01). The results from analysis of NOC in 212 fresh samples in relation to pH demonstrated two significantly higher peaks of NOC concentrations at intragastric pH ranges 1.1 to 2.99 (P < 0.05) and 6.0 to 7.9 (P < 0.01). There was a significant relationship between nitrite level and intragastric pH (r = 0.480, P < 0.01), the nitrite concentration increasing dramatically when the pH exceeded 6.0. The present study suggest that a major proportion of the unidentified NOC formed through intragastric nitrosation is labile NOC; if the true concentration of NOC is to be determined it is therefore essential to analyse fresh gastric juice samples directly after collection and without pretreatment. It will also be necessary to characterize those labile NOC in order to study further the mechanism of endogenous N-nitrosation in man and its relation to human carcinogenesis.