Gastrin has no promoting effect on chemically induced colonic tumors in Wistar rats

The effects of prolonged administration of tetragastrin from the beginning of intrarectal instillation of 1 ml of 0.25% N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) and after MNNG-treatment on the incidence and histology of colonic tumors were compared in inbred Wistar rats. In week 35 prolonged administration of testragastrin in depot form from the beginning of MNNG-treatment resulted in a significant reduction in the incidence of colonic tumors and a significant increase in the incidence of mucinous adenocarcinoma, unlike the well-differentiated adenocarcinoma produced in controls without gastrin. In contrast, prolonged administration of tetragastrin after MNNG-treatment had little or no influence on the incidence, size or histology of colonic tumors. Thus tetragastrin had no promoting effect on colonic tumors.