Effects of cimetidine and indomethacin on the growth of dimethylhydrazine-induced or transplanted intestinal cancers in the rat.

The effects of cimetidine and indomethacin on the growth of dimethylhydrazine induced or transplanted intestinal tumours in the rat have been studied. Cimetidine is a histamine type 2 receptor antagonist and indomethacin is an inhibitor of prostaglandin synthesis. Two models of rat intestinal tumours were used: a colon carcinoma line transplantable in syngeneic animals and intestinal tumours induced by dimethylhydrazine treatment of Sprague-Dawley rats. Cimetidine and indomethacin were given in drinking water, alone or in combination. Cimetidine had no effect on the growth of transplanted colon cancer but significantly increased the incidence of chemically-induced tumours, with a tendency toward more invasive and metastatic tumours than in the control animals. Indomethacin did not significantly modify the incidence or other characteristics of the tumours in any of the models. This result is at variance with a protective effect of indomethacin on chemically-induced rat colon cancer previously reported by others.