AJP - Gastrointestinal and Liver Physiology, Vol 251, Issue 4 460-G466, Copyright © 1986 by American Physiological Society
Hormonal regulation of postprandial induction of gastrointestinal ornithine decarboxylase activity
E. R. Seidel
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.
