NITRITE SOURCES AND NITROSAMINE FORMATION INVITRO AND INVIVO

The ingestion by normal adults of a meal including vegetables rich in nitrate led to a rapid increase in the salivary nitrite concentration. This was followed by a fall towards the fasting nitrite levels, although the concentration in the saliva remained elevated for as long as 21 hr. Using foods as sources of nitrosatable amines, studies have been made both in vitro and in vivo on the formation of N-nitroso compounds under the conditions encountered in the human stomach, with special reference to the different thiocyanate concentrations in smokers and non-smokers. The nitrite level and pH of gastric contents increased markedly following the consumption of a meal containing nitrite, reaching maxima within about 45 min and then returning towards fasting levels. N-Nitrosopiperidine (NPIP) and N-nitrosopyrrolidine were the major volatile nitrosamines produced when foods were incubated with nitrite under acid conditions in vitro. At the nitrite concentrations likely to occur in the stomach, nitrosamine formation was reduced and was significantly lower in the absence of thiocyanate than in its presence at levels of 0·2-3 mm. Trace amounts of NPIP were detected occasionally in the gastric contents of volunteers after ingestion of homogenized foods containing nitrite. Both volatile and non-volatile N-nitroso compounds were obtained from a tobacco-smoke condensate following incubations in vitro simulating those likely to occur within the human stomach. Under the same conditions, N-nitrosation occurred in incubations containing the antidepressant nortriptyline, but this was greatly reduced in the presence of ascorbic acid. © 1971.