1,2-Dimethylhydrazine-induced nuclear aberrations in A/J and C57BL/6J mouse colonic crypts.

A single exposure to 1,2-dimethylhydrazine [(DMH) CAS: 540-73-8] produces several forms of aberrant nuclei in the crypts of the murine colon. The frequency of nuclear aberrations (NAs) was examined in the distal colonic crypts in DMH-sensitive A/J mice and relatively DMH-resistant C57BL/6J mice before and after a single exposure to DMH. NAs, mitotic figures, and crypt column heights were scored for all animals as a function of time following administration of DMH. In both strains there was a significant increase in the absolute and relative frequency of NAs by 12 hours, with a corresponding drop and subsequent overshoot in the mitotic index by 48 hours after DMH. The temporal changes in crypt column height correlate closely with the temporal changes in frequency of NAs in both strains. The results showed that both inbred strains respond to acute DMH exposure in a similar and parallel fashion over time. It was concluded that the NA index assay is a sensitive method for detecting early DMH exposure. However, this assay does not relate to ultimate outcome after chronic DMH exposure and should not be used as a predictor of eventual neoplastic transformation of colonic mucosa with this carcinogen.