Intestinal tumors induced by a single intraperitoneal injection of methyl(acetoxymethyl)nitrosamine in three strains of rats.

Methyl(acetoxymethyl)nitrosamine (DMN-OAc) when in jected i.p. in Sprague-Dawley Charles River CD rats selectively induces epithelial tumors of the intestines. Males are more severely affected than females. To determine whether the strain of rat determines the quantity or type of tumors induced, 5week-old male and female rats of Sprague-Dawley (SD), Buffalo (BUF) and Fischer (F344) strains were given a single i.p. injection of DMN-OAc. The dose used, 13 mg (0.1 mmol)/kg body weight, was one-half of the acute i.p. median lethal dose determined for 5-week-old male SD rats. In each strain treated with DMN-OAc, a large number of intestinal epithelial tumors developed. The histological features of these tumors were the same in all strains and both sexes. In each strain, females had fewer induced tumors of the small and large intestines than had males of the same strain. The greatest difference between males and females in frequency of small intestine tumors in duced was observed in F344 rats. There were 1.7 small intes tine tumors/male F344 rat and only 0.2 small intestine tumors/ female F344 rat. The lowest induced tumor incidence was seen in BUF rats (0.3 small intestine tumors/male rat and 0.2 small intestine tumors/female rat). In SD rats, there were 2.0 small intestine tumors/male and 1.3 small intestine tumors/female. In all strains and both sexes, there were many more small intestine tumors induced than tumors of the large intestine. Tumors occurred throughout the small intestine and colon and in the cecum, with a tendency to occur most frequently in the distal ileum. Localization was the same in all strains and sexes studied. Other tumors induced with high frequency by i.p. administration of DMN-OAc were schwannomas (primary in peritoneum), testicular mesotheliomas, and splenic angiosar comas.