Enhancement by vasoactive intestinal peptide of experimental carcinogenesis induced by azoxymethane in rat colon.

The effects of vasoactive intestinal peptide (VIP) on the incidence and histology of colonic tumors induced by azoxymethane (AOM) were investigated in Wistar rats. Rats were given 20 micrograms/kg body weight of VIP every other day for 12 weeks and from experimental week 3, were given 10 weekly injections of 7.4 mg/kg body weight of AOM. The administration of VIP before and during AOM treatment resulted in a significant increase in the incidence of colonic tumors in week 40. Furthermore, it caused a significant increase in the labeling index of the colonic mucosa during AOM treatment. These findings indicate that VIP enhanced the development of colonic tumors. This effect may have been related to its effect in increasing proliferation of cells in the colonic mucosa during administration of the carcinogen.