Syncarcinogenesis at low exposure levels of three nitrosamines with a common target of carcinogenic action: preliminary results.

The carcinogenic activities of N-nitrosodiethylamine (NDEA), N-nitrosopyrrolidine (NPYR) and N-nitrosodiethanolamine (NDELA) and of the combination of the three nitrosamines was determined in Sprague-Dawley rats at three logarithmically spaced exposure levels. The highest doses of the individual nitrosamines and of their combination, chosen so as to induce low specific incidences of liver tumours following life-long administration, resulted in median survival times for all treated groups of more than 30 months. The macroscopically determined incidences of liver tumours were 1% in control rats, 45%, 4% and 4% following administration of NDEA, 14%, 3% and 1% following administration of NPYR, 6%, 5% and 1% following administration of NDELA and 12%, 4% and 3% following the combined administration of all three nitrosamines. These results indicate linear, additive carcinogenicity with respect to their common target organ in the dose range investigated.