Hormonal regulation of postprandial induction of gastrointestinal ornithine decarboxylase activity.

The growth of gastrointestinal mucosa can be related to ingestion and digestion of diet, with fasting producing mucosal hypoplasia and hyperphagia producing mucosal hyperplasia. Experiments were designed to determine whether induction of polyamine metabolism following ingestion of a meal was related to mucosal growth. Activity of the enzyme ornithine decarboxylase (ODC) in both jejunum and ileum but not in duodenum was dependent on the presence of food in the gut; ODC activity was more than 200-fold greater in mucosa of fed rats than in fasted rats. Inhibition of ODC with difluoromethylornithine lead to mucosal atrophy in ileum but not in duodenum. Refeeding of fasted rats resulted in significant induction of ODC in duodenal, ileal, and colonic, but not fundic, mucosa. In addition, two hormones, epidermal growth factor and glucagon, were effective inducers of ileal ODC activity. Direct evidence for hormonal involvement in the postprandial rise in mucosal ODC activity was provided by experiments in rats that had undergone ileal bypass surgery. After refeeding of fasted rats mucosal ODC activity was induced in both ileum left in continuity and in the bypassed segment. Refeeding of elemental diets demonstrated that ingestion of carbohydrate alone was sufficient for maximal enzyme induction. Mixed amino acids or glyceryl trioleate were no more effective inducers than nonnutritive solutions of cellulose or saccharin. These data demonstrate that hormones which are released during ingestion and digestion of a meal are the stimuli for induction of mucosal polyamine metabolism, suggesting that food-induced mucosal growth is hormonally mediated.