Pathological and enzymatic features of 1,2-dimethylhydrazine induced colorectal carcinomas in rats.

Well- and moderately well-differentiated colorectal adenocarcinomas accounted for 86% of all tumors induced by 1,2-dimethylhydrazine in rats, and were distributed throughout the colorectal tract. Poorly differentiated carcinomas, 14% of all tumors, were markedly restricted to the proximal half of colon, i.e., 94% of the poorly differentiated type was found in the proximal colon and caecum. Thymidylate synthetase and thymidine kinase, key enzymes in the de novo and salvage pathways, respectively, for pyrimidine nucleotide synthesis were found to be reduced and elevated, respectively, with increasing cellular differentiation. These results suggest that biochemical differences in colorectal tumors may be associated with differences in tumor frequency, distribution, and histological type.