Ultrastructure of 1,2-Dimethylhydrazine-Induced Adenocarcinomas in Rat Colon2

Abstract

The ultrastructure of 1,2-dimethylhydrazine-induced adenocarcinomas In the SD rat colon was examined with the use of transmission electron microscopy of thin sections. The ultrastructure of tumor cells in colon adenocarcinomas and the ultrastructure of epithelial cells in the normal colon were compared. In addition, the ultrastructure of tumor cells In the S-phase was examined by means of tritiated thymidine and electron microscope autoradiography. The results showed that most tumor cells morphologically resembled undifferentiated crypt cells of normal colon epithelium, and a minority of tumor cells closely resembled, and were often Indistinguishable from, differentiated colon epithelial cells. Consistent abnormalities In the morphology of the basal lamina at the Interface between tumor epithelium and adjacent lamina propria mucosae were observed. In some sections examined, most tumor cells showed ultrastructural but not light microscopic evidence of degeneration. Comparisons between the morphology of colon tumor cells and normal colon epithelial cells failed to reveal a single morphologic feature characteristic of tumor cells. Electron microscope autoradiography of sections of colon adenocarcinomas revealed that tumor cells having widely divergent morphologic appearancei were capable of thymidine uptake; these tumor cells Included “dark” cells and cells showing morphologic changes usually associated with necrosis.