BOMBESIN ENHANCES EXPERIMENTAL CARCINOGENESIS INDUCED IN RAT COLON BY1,2-DIMETHYLHYDRAZINE

The effects of bombesin on the colonic mucosa and on the incidence, nu mber, size and histology of colon cancers induced by 1,2-dimethylhydra zine (DMH) were studied in Fischer 344 rats. In experiment 1, rats wer e randomized into three groups to receive either saline or bombesin (1 0 or 30 mu g/kg body wt) to determine the labeling index of normal col onic mucosa. In experiment 2, rats were given 20 weekly injections of DMH (20 mu g/kg body wt) and received either saline or bombesin (10 or 30 mu g/kg body wt) every other day for 24 weeks. Administration of b ombesin significantly increased the labeling indices of colonic mucosa in a dose-dependent manner. Chronic administration of bombesin at bot h dosages with DMH caused significant increases in the incidence, numb er and depth of involvement of colon cancers; however, it did not affe ct the size and histological type of colon cancers. In addition, bombe sin at the dose of 30 mu g/kg significantly increased the labeling ind ex of colon cancer. These results suggest that bombesin stimulates the cell proliferation of colonic mucosa and colon cancer and enhances co lon carcinogenesis in rats.