Lack of Any Positive Effect of Intestinal Metaplasia on Induction of Gastric Tumors in Wistar Rats Treated with N‐Methyl‐N‐nitrosourea in Their Drinking Water

The influence of intestinal metaplasia on gastric cancer induction was examined in five‐week‐old male Wistan:Crj rats. The animals were first treated with two 10 Gy doses of X‐rays to the gastric region at a 3‐day interval (total 20 Gy) and then, starting two months after the irradiation, received 100 ppm N‐methyl‐N‐nitrosourea (MNU) in their drinking water for 15 weeks. Thereafter they were maintained for 37 weeks with or without a dietary 1% sodium chloride (NaCl) supplement. The incidences of gastric adenocarcinomas in the MNU or MNU plus NaCl groups were significantly higher than in animals receiving X‐rays plus MNU with or without NaCl. Intestinal metaplasias and the numbers of alkaline phosphatase(ALP)‐positive foci were significantly increased in the X‐ray irradiation groups but the numbers of ALP‐positive foci were not increased with or without 1% NaCl. An inverse relationship between incidences of gastric tumors and intestinal metaplasias was apparent. The present experiment thus showed that the presence of intestinal metaplasia does not exert a positive influence on induction of gastric neoplasia by MNU in the rat.