Germ-Free Status and Colon Tumor Induction by N-Methyl-N'-Nitro-N-Nitrosoguanidine 1

Summary Female germfree and conventional rats of 50 days of age were injected intrarectally with MNNG for 20 wk (total dose, 48 mg/rat) and autopsied 30 wk after last injection. The colon adenomas induced by MNNG were doubled in germ-free rats compared to conventional animals. However, germfree status had no effect on the incidence of adenocarcinomas. It is concluded that pharmacodynamics and metabolism of carcinogen play a role greater than the immune status of the animal in the action of carcinogens such as MNNG.