EFFECT OF AGING ON THE DEVELOPMENT OF GASTRIC CANCER IN RATS INDUCED BY N-METHYL-N'-NITRO-N-NITROSOGUANIDINE

: This experiment was carried out to see the effect of aging on the induction of gastric carcinoma in rats by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). Three groups of rats of 3 different ages, 6, 20, and 40 weeks old, were used. Comparison of incidence of gastric carcinoma in these groups revealed a significant difference. Tumor incidence of the gastrointestinal tract of rats were 94.7, 73.8, and 48.8%, resepctively, at 6, 20, and 40 weeks of age. The incidence of adenocarcinomas of glandular stomach was also significantly decreased with the advance in age. However, there was a significant difference in the intake rate of MNNG per gram body weight between the young (6 weeks of age) and old rats for the first 25 weeks during the experiment which may account for the difference in tumor incidence between young and old rats. However, even when the young rats were administered a decreased amount of MNNG, same as that in old rats, they also showed higher incidence. From these results, it was concluded that the amount of MNNG ingested was not responsible for the decreased incidence of gastric adenocarcinoma in older rats. Aging might be the primarily the cause of low incidence.