Individual susceptibility of mice to a mutagen in both germ and somatic cells

Male Swiss mice received simultaneously, by gavage, 500 mg methylurea/kg body weight and 25 mg sodium nitrite/kg body weight, and in a further experiment 330 mg of methylurea/kg and 17 mg sodium nitrite/kg, for 5 consecutive days. This treatment resulted in a dose-dependent mutagenic effect in both the dominant-lethal and the micro-nucleus tests. Furthermore, in both mammalian tests, some animals were more susceptible to the mutagenic compounds than were others. However, the liver microsomal metabolizing system did not seem to be responsible for this variation of mutagenic induction.