Germ-free status and colon tumor induction by N-methyl-N'-nitro-N-nitrosoguanidine

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 germfree 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.