Role of morphological methods in the analysis of chemically induced colon cancer in rats.

The role of selected histopathological methods was evaluated for the characterization of tumourous tissues resulting from chemically induced carcinogenesis in rats. Colon cancer was induced by treating rats with a direct carcinogen, N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), alone or with subsequent treatments with secondary bile acids. Morphological studies showed that the tumorigenic effect of MNNG resulted in changes in the shape of the crypts, disappearance of mucous (goblet) cells, and marked increases in the mitotic index, the size of nuclei and the number of aberrant nuclei. A significant number of lymphocytes infiltrated between the crypts and into their lumens. A sharp decrease in concentrations of neutral mucopolysaccharides and sulfomucins and an increase in the amount of vic-glycol groups and nonsulfated mucosubstances were demonstrated in tumourous epithelial cells. A moderate positive reaction to tissue polypeptide antibody was observed in these cells. The tumor-promoting effects of secondary bile acids were detected morphologically by an increase in the amount of connective tissue that infiltrated newly formed tumors. The increased number of micronuclei in otherwise histologically unaltered colon tissues adjacent to a tumor suggests that these regions represent a precancerous stage in the development of tumors. The important role of morphological methods in the evaluation of the effects of carcinogen and tumor promoters and in the detection of various phases in experimental carcinogenesis was discussed.