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ABSTRACT
Journal of Nutrition. 2000;130:978S-982S.
Supplement
Intestinal Glutamate Metabolism
Peter J. Reeds, Douglas G. Burrin, Barbara Stoll and Farook Jahoor
U.S. Department of Agriculture/Agricultural Research Service,
Children’s Nutrition Research Center, Department of Pediatrics, Baylor College
of Medicine, Houston, TX
Although it is well known that the intestinal tract has a high metabolic
rate, the substrates that are used to generate the necessary energy
remain poorly established, especially in fed animals. Under fed
conditions, the quantification of substrate used by the gut is
complicated by the fact that potential oxidative precursors are
supplied from both the diet and the arterial 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-13C]substrates. We studied rapidly growing piglets
that were consuming diets based on whole-milk proteins. The results
revealed that 95% of the dietary glutamate presented to the mucosa was
metabolized in first pass and that of this, 50% was metabolized to
CO2. Dietary glucose was oxidized to a very limited
extent, and arterial glutamine supplied no >15% of the
CO2 production by the portal-drained viscera. Glutamate was
the single largest
contributor to intestinal
energy generation. The results also suggested that dietary glutamate appeared to be a
specific precursor for the biosynthesis of glutathione, arginine and
proline by the small intestinal
mucosa. These studies imply that dietary glutamate has an important
functional role in the gut. Furthermore, these functions are
apparently different from those of arterial glutamine, the substrate
that has received the most attention.
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