ENDOGENOUS N-NITROSATION IN MAN ASSESSED BY MEASUREMENT OF APPARENT TOTAL N-NITROSO COMPOUNDS IN FECES

The faecal concentration of substances responding to the chemical test for N-nitroso compounds (apparent total N-nitroso compounds, ATNC) was investigated in human subjects consuming their normal free-choice diet. Concentrations ranged from 40 to 590-mu-g (N-NO)/kg faeces. To ascertain the likely relative contributions of endogenous ATNC formation and preformed, dietary ATNC, the subjects consumed a diet low in nitrate and ATNC for 8 days. At the end of this period, ATNC had decreased substantially with concentrations ranging from below the 40-mu-g (N-NO)/kg detection limit up to 143-mu-g (N-NO)/kg, mean 82-mu-g (N-NO)/kg. On supplementing this diet with 300 mg nitrate/day, faecal ATNC levels increased markedly. On the third day of this regime, values were in the range 73-714-mu-g (N-NO)/kg with a mean of 307-mu-g (N-NO)/kg. The results, together with the known limited occurrence of ATNC in the majority of foodstuffs so far tested, generally non-detectable or < 100-mu-g (N-NO)/kg, suggest that endogenous formation via species derived from dietary nitrate is likely to be an important source of ATNC in human faeces.