A scanning electron microscopy study of changes in the colonic mucus layer during chemical carcinogenesis.

Scanning electron microscopy was used to examine the appearances of the colonic mucus layer of rats during chemical carcinogenesis with dimethylhydrazine. The normal colonic mucus layer had a dense homogeneous appearance and provided a complete cover for the mucosal epithelium. At high magnifications tiny fenestrations could be seen in this mucus layer. During carcinogenesis these fenestrations enlarged, increased in number, and coalesced, causing focal defects in the mucus layer, which eventually broke into strands and clumps of mucus. The findings indicate that the colonic mucus layer develops progressive abnormalities during carcinogenesis which result in breakdown of its integrity and exposure of the mucosal epithelium to colonic contents.