THE RELATIONSHIP BETWEEN MEGACOLON AND CARCINOMA OF THE COLON - AN EXPERIMENTAL APPROACH

'Carcinoma of the colon does not occur in cases of megacolon' is an ax iom held by Brazilian physicians working in endemic areas for Chagas' disease. The objective of the present study was to test this axiom exp erimentally by submitting rats with experimental megacolon to a carcin ogen which causes carcinoma of the colon. Eighty young male Wistar rat s received serosal application of either saline (0.9% NaCl) or 2 mM be nzalkonium chloride (BAG) to the distal colon. Ten months later random ly chosen saline and BAC rats were injected weekly with dimethylhydraz ine (DMH) for 20 weeks. Non-DMH-treated rats from both original groups were maintained, for a total of four experimental groups. Three month s after the injections all surviving rats were killed. At autopsy the presence or absence of carcinomas along the colon was recorded. The in duction of megacolon was evaluated by morphometry of the wall from the distal colon and myenteric denervation was assessed by neuron counts. An increase of at least 2-fold in distal colon wall thickness confirm ed the induction of megacolon in BAG-treated rats. Neuronal counts fro m BAG and control rats not treated with DMH showed an average denervat ion of 63%. The number of distal colon carcinomas in BAC + DMH-treated rats was significantly lower than that in DMH-treated rats. These fin dings appear to contradict the traditional concept of carcinogenesis o f the colon. The clinical axiom was reproduced experimentally.