AJP - Gastrointestinal and Liver Physiology, Vol 253, Issue 3 303-G307, Copyright © 1987 by American Physiological Society
Stimulation of ornithine decarboxylase activity in digestive tract mucosa
R. Jain, B. E. Eikenburg and L. R. Johnson
Refeeding fasted rats with normal rat food and with a variety of amino
acids increases ornithine decarboxylase (ODC) activity considerably. The
time course of that increase, the areas of the digestive tract directly
affected, and the effective concentrations of stimulants are unknown. By
use of isolated 5-cm segments of rat jejunum, we determined that maximal
activation of ODC occurred after a 2-h exposure to 0.6 M glycine. Increased
activity was first apparent after a 1-h exposure to glycine and was
significant after a 2-h exposure to 0.05 M glycine. ODC activity increased
the most in segments of jejunum, followed by segments of ileum and then
duodenum. Glycine (0.4 M) failed to increase ODC activity in gastric and
colonic mucosa. Interestingly, D-alanine was more effective than L-alanine
in stimulating ODC activity in the jejunum. Enzyme activity was not
dependent on osmotic activity of the test substances. Glucose increased
enzyme activity, but mannitol and fructose were without effect. The effects
of glycine were significantly greater than those of glucose. In summary,
ODC of the small intestinal mucosa is increased by direct contact with
amino acids and glucose within 2 h after exposure. Increased enzyme
activity depends on the nature of the stimulant rather than the osmotic
activity of the solution in contact with the mucosa.
