In vivo formation of N-nitroso compounds and detection of their mutagenic activity in the host-mediated assay.

The formation of /V-nitroso compounds in mouse stom ach from equimolar doses of sodium nitrite and secondary amines or alkylurea derivatives given simultaneously by a stomach tube was estimated by measuring the mutagenic activity of the compounds in the i.p. host-mediated assay with the use of Salmonella typhimurium TA1950 as genetic indicator system. A mutagenic response in the bacteria was found after administration of the cyclic amines piperazine dihydrochloride, morpholine, and amitrole. The high est mutagenicity was exerted by piperazine dihydrochloride plus nitrite, while amitrole plus nitrite was only weakly mutagenic. No mutagenic activity was observed for equi molar doses of sodium nitrite plus dimethylamine hydrochloride, diphenylamine. methylbenzylamine hydrochloride, and phenmetrazine hydrochloride. All /V-alkylurea de rivatives tested were found to yield significant amounts of /V-nitroso compounds, which allowed detection of their mutagenic activity in the host-mediated assay. The highest activity was shown by nitrite plus ethylenebis(thiourea), while methylurea and ethylurea were found to be less active in combination with nitrite. Dose-response curves for the mutagenic activity of /V-nitrosamines were used to estimate the amounts of /V-nitroso derivatives formed in vivo from the precursors after acute treatment of the mice. In the case of piperazine dihydrochloride, nitrosation of 50 to 70% was estimated, while for morpholine nitrosation ranged from 1 to 3%. The results are compared with those obtained in long-term carcinogenesis studies with sodium nitrite plus amines.