Biochemical changes in preneoplastic rodent intestines.

Two enzymes were examined as potential indicators of early precancerous changes. Ornithine decarboxylase, an enzyme normally associated with rapid cell division, is low in the rapidly dividing, cancer-susceptible colon. The level of this enzyme was also very high in the nondividing cells of the small intestines. Administration of an intestinal carcinogen, dimethylhydrazine, led to a large increase in colonic ornithine decarboxylase but did not affect the enzyme in liver. A liver carcinogen, acetylaminofluorene, induced manyfold increases in ornithine decarboxylase of the liver but not of the colon. Studies of thymidine kinase of the gut showed that this enzyme changed quantitatively and qualitatively throughout the life of the animal, from fetal rat to newborn and adult. The tumor enzyme has many fetal-like properties. Long-term treatment with dimethylhydrazine led to changes in thymidine kinase reminiscent of the fetal enzyme. Short-term treatment caused sharp increases in the thymidine kinase of nondividing cells of the jejunum and the proximal end of the colon; similar changes in the distal end of the colon were slower in appearing and less pronounced.