Induction of tumors in the stomach and nervous system of the ACI/N rat by continuous oral administration of 1-methyl-3-acetyl-1-nitrosourea.

Three groups of ACI/N rats of both sexes received continuous administration of 66 (Group I), 30 Group II), or 13(Group III) ppm solution of 1-methyl-3-acetyl-1-nitrosourea (Ac-MNU) in their drinking water. Tumors were found most frequently in the stomach and nervous system. The former was more frequently found in the male than in the female. The incidence was highest in males of Group II, 28/30 (93%), and lowest in females of Group I, 4/30 (13%). Histologically, all epithelial tumors of the stomach were benign adenomas except 5 adenocarcinomas. Neurogenous tumors were more frequently seen in the female than in the male. The incidence was highest in females of Group I, 29/30 (97%), and lowest in males of Group III, 6/28 (21%). The tumors were predominant in the central nervous system, especially in the hemispheres. Transplantation studies were done in some of these tumors. Although gastric tumors failed to get positive transplantation, all the neurogenous tumors transplanted were positive.