A scanning electron microscopy study of changes in rat colonic mucosa during carcinogenesis.

Scanning electron microscopy (SEM) has been used to examine morphological changes on the colonic mucosal surface during experimental carcinogenesis. Seventy-five rats were given weekly injections of dimethylhydrazine (DMH) and 25 rats acted as controls. Groups of DMH-treated and control rats were sacrificed at regular intervals and specimens of their colons were examined by SEM. The normal colonic mucosa had an orderly architectural pattern which remained constant throughout the experiment. Abnormalities in the mucosa of treated rats were detected as early as 6 weeks after the first injection of DMH and thereafter there was progressive distortion of the crypts, development of pericryptal fissures and mucosal surface irregularities, and eventually, formation of focal protuberances, polyps, and tumors. The findings indicate that there is a definite pattern of progressive mucosal abnormalities commencing long before the development of focal colon tumors and that SEM is useful in the detection of these abnormalities.