The effect of experimental carcinogenesis on intestinal diamine oxidase, a polyamine deaminating enzyme.

Intestinal mucosa hyperproliferation is an important risk factor of large bowel carcinoma development. Intestinal diamine oxidase (DAO) is suggested to be a proliferation terminating principle in the mature mucosa. Therefore, the influence of the carcinogen azoxymethane (AOM) on this enzyme was studied. The enzyme was measured with the 14C-putrescine assay. In vitro the enzyme was inhibited only by excessive high concentrations of AOM (89 mmol/liter). In vivo the enzymic activity was reduced in the duodenum but not in the colon during the first 48 hr after AOM application (15 mg/kg). Ten weekly injections of AOM reduced the DAO activity in the duodenum and colon significantly (alpha = 0.05). After the stop of the AOM application a significant (alpha = 0.05) increase of DAO activity over the control level was found which was interpreted as a defense reaction of the mucosa against the hyperproliferation that had occurred during the carcinogen treatment. Intestinal DAO is regarded as an antiproliferative principle protecting the integrity of the intestinal mucosa. An inhibition of this enzyme probably increases the risk of intestinal carcinoma promotion.