Acute changes occurring in the intestinal mucosae of rats given a single injection of 1,2 dimethylhydrazine.

In the long term, administration of dimethylhydrazine (DMH) to rats results in the development of tumours in both small intestine and colon. This study has been undertaken in order to document the sequence of changes occurring in the intestinal mucosa in the first 108 h following a single subcutaneous injection of DMH. After a lag of several hours there is evidence of damage to cells in the proliferation zone of the intestinal crypts, and a brief reduction in tritiated thymidine labelling index. A phase of compensatory regenerative activity emerges from the setting of continuing cell damage, resulting in restoration of the mucosa to normal. The severity of the toxic damage to the intestinal mucosa at various sites mirrors the vulnerability of the mucosa to the long term carcinogenic effects of DMH, suggesting that inherent properties of the mucosa may be of more importance than other cocarcinogenic influences in the ultimate development of tumours.