The effect of Helicobacter pylori
infection on
N-methyl-N'-nitro-N-nitrosoguanidine (
MNNG)-induced
gastric cancer was studied using a Mongolian gerbil model. Five-week-old male Mongolian gerbils were divided into four groups of 25-30 animals each and challenged for 20 weeks with H.pylori,
MNNG, a combination of H.pylori and
MNNG, or neither of them. Four to 20 animals from each group were killed at 16, 24 and 52 weeks after H.pylori inoculation, and histopathological changes in their stomachs were examined. A well-differentiated
adenocarcinoma was first observed 24 weeks after inoculation in the combination group. At 52 weeks, only six of 15 animals were colonized with H.pylori persistently, and four of them showed well-differentiated
adenocarcinomas; on the other hand, neither of the animals with disappearance of H.pylori from the combination group showed
adenocarcinoma. At the same observation time, three of 17 animals from
MNNG group showed poorly differentiated
adenocarcinomas. The incidence of gastric
carcinoma in the combination group was significantly higher than that in the
MNNG group (P < 0.05). However, no
tumors were seen in the control and H.pylori groups. The present findings demonstrate that H.pylori
infection enhances the carcinogenic action of
MNNG.