Bombesin enhances experimental carcinogenesis induced in rat colon by 1,2-dimethylhydrazine

The effects of bombesin on the colonic mucosa and on the incidence,number, size and histology of colon cancers induced by 1,2-dimethylhydrazine(DMH) were studied in Fischer 344 rats. In experiment 1, ratswere randomized into three groups to receive either saline orbombesin (10 or 30 µg/kg body wt) to determine the labelingindex of normal colonic mucosa. In experiment 2, rats were given20 weekly injections of DMH (20 µg/kg body wt) and receivedeither saline or bombesin (10 or 30 µg/kg body wt) everyother day for 24 weeks. Administration of bombesin significantlyincreased the labeling indices of colonic mucosa in a dose-dependentmanner. Chronic administration of bombesin at both dosages withDMH caused significant increases in the incidence, number anddepth of involvement of colon cancers; however, it did not affectthe size and histological type of colon cancers. In addition,bombesin at the dose of 30 µg/kg significantly increasedthe labeling index of colon cancer. These results suggest thatbombesin stimulates the cell proliferation of colonic mucosaand colon cancer and enhances colon carcinogenesis in rats.