Intestinal glutamate metabolism

Although it is well known that the intestinal tract has a high metabolic ra te, the substrates that are used to generate the necessary energy remain po orly established, especially in fed animals. Under fed conditions, the quan tification of substrate used by the gut is complicated by the fact that pot ential oxidative precursors are supplied from both the diet and the arteria l circulation. To circumvent this problem, and to approach the question of the compounds used to generate ATP in the gut, we combined measurements of portal nutrient balance with enteral and intravenous infusions of [U-C-13]s ubstrates. We studied rapidly growing piglets that were consuming diets bas ed on whole-milk proteins. The results revealed that 95% of the dietary glu tamate presented to the mucosa was metabolized in first pass and that of th is, 50% was metabolized to CO2. Dietary glucose was oxidized to a very limi ted extent, and arterial glutamine supplied no >15% of the CO2 production b y the portal-drained viscera. Glutamate was the single largest contributor to intestinal energy generation. The results also suggested that dietary gl utamate appeared to be a specific precursor for the biosynthesis of glutath ione, arginine and proline by the small intestinal mucosa. These studies im ply that dietary glutamate has an important functional role in the gut. Fur thermore, these functions are apparently different from those of arterial g lutamine, the substrate that has received the most attention.