Studies on the effect of feeding nitrite and secondary amines to Wistar rats.

1. When 1 000 mg/l sodium nitrite are added to drinking-water, nitrosamines are formed in the stomachs of Wistar rats at levels greater than the background only if the concentrations of added DMA or pyrrolidine exceed 1 000 mg/kg. Once this concentration is exceeded there is a rapid increase in nitrosamine formation up to 2 000 mg/kg added amine; however, for pyrrolidine, the rate of increase of NPy decreases when the dietary level of amine exceeds 2 000 mg/kg. This threshold level of 1 000 mg/kg amine is one which is rarely reached in normal human dietary patterns. 2. Due to the presence of this threshold it is unrealistic to extrapolate from high experimental dietary concentrations of secondary amines to those found in practice when considering nitrosamine formation in vivo. 3.The concentration of dietary amine has a greater influence on nitrosamine formation in the stomachs of rats than does the concentration of nitrite in drinking-water (up to 1 000 mg/l). This finding is in contradiction to the current kinetic theory of nitrosamine formation, in which formation is predicted to be proportional to the square of the nitrite concentration.