Pj. Reeds et al., ENTERAL GLUTAMATE IS ALMOST COMPLETELY METABOLIZED IN FIRST PASS BY THE GASTROINTESTINAL-TRACT OF INFANT PIGS, American journal of physiology: endocrinology and metabolism, 33(3), 1996, pp. 413-418
We studied the absorption of enteral glutamate and phenylalanine using
isotopic tracer and arteriovenous difference techniques. Six piglets,
implanted with portal, carotid, and gastric catheters and an ultrason
ic portal flow probe received a 6-h intragastric infusion of [U-C-13]g
lutamate ana [H-2]phenylalanine, with a high-protein diet offered one
time each hour. Amino acid concentrations and the isotopic enrichments
of all mass isotopomers of glutamate, glutamine, and phenylalanine we
re measured in portal and arterial blood over the last hour. There was
significant (P < 0.025) net absorption of the indispensable amino aci
ds as well as arginine, proline, serine, and alanine. There was no por
tal uptake of glutamate, aspartate, and glycine, and arterial glutamin
e was removed by the portal drained viscera (P < 0.05). At isotopic st
eady state, 72% of the [H-2]phenylalanine but only 5% of the [U-C-13]g
lutamate tracer appeared in the portal blood. We conclude that, in fed
infant pigs, the gut metabolizes virtually all of the enteral glutama
te during absorption. Therefore, glutamate and glutamine in the body a
s a whole must derive almost entirely from synthesis de novo.