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, rats were randomized into three groups to receive either saline or bombesin (10 or 30 micrograms/kg body wt) to determine the labeling index of normal colonic mucosa. In experiment 2, rats were given 20 weekly injections of DMH (20 micrograms/kg body wt) and received either saline or bombesin (10 or 30 micrograms/kg body wt) every other day for 24 weeks. Administration of bombesin significantly increased the labeling indices of colonic mucosa in a dose-dependent manner. Chronic administration of bombesin at both dosages with DMH caused significant increases in the incidence, number and depth of involvement of colon cancers; however, it did not affect the size and histological type of colon cancers. In addition, bombesin at the dose of 30 micrograms/kg significantly increased the labeling index of colon cancer. These results suggest that bombesin stimulates the cell proliferation of colonic mucosa and colon cancer and enhances colon carcinogenesis in rats.