[Induction of colonic carcinoma in mice using 1,2-dimethylhydrazine hydrochloride]

Weekly injections of 1,2-dimethylhydrazine-HC1 were given to female NMRI mice (Versuchstierfarm Tuttlingen, Germany). The earliest histological changes are those of focal hyperplasia and focal atypias confined to single crypts. These changes are observed as early as 5 weeks after the first injection. Serial sections of the whole colon were analyzed for localization and incidence of these lesions. Whereas after 12 weeks the number of small lesions was greater than after 36 weeks of exposure, at 36 weeks there were in situ carcinomas and carcinomas with infiltration. It appears that the focal atypias confined to single crypts may heal. With H-3-TdR labelling, it could be demonstrated that before generalized changes are observed histologically, there is a widening of the proliferative compartment. After cessation of DMH exposure, these changes continue for many weeks.