Production of intestinal and other tumors by 1, 2-dimethylhydrazine dihydrochloride in mice. I. A light and transmission electron microscopic study of colonic neoplasms.

Single or ten weekly subcutaneous injection(s) of 1, 2-dimethylhydrazine dihydrochloride were administered separately to Swiss mice. The repeated application gave rise mainly to high incidences of tumors in the large intestine. These neoplasms occurred most frequently in the colorectal area and in cecum adjacent to ileum. Light microscopically, these lesions were classified as polypoid adenomas and adenocarcinomas. Most of the adenocarcinomas were highly invasive, although they metastasized rarely. The fine structure of the malignant cells exhibited features typical of columnar absorptive cells. A distinctive alteration was the disorderly arrangement and abnormal size and shape of the microvilli. In addition, the cells exhibited numerous free ribosomes, little RER, priminent Golgi bodies, and uniformly dispersed nuclear chromatin. Morphologically, the intestinal tumors were similar to those found in man. In addition, the repeated administration of 1, 2-DMH also induced significant incidences of neoplasms in blood vessels, lungs, anus, and kidneys while the single application produced tumors in blood vessels and liver. The main hypotheses attempting to explain the selective induction of large intestinal neoplasms are discussed.