Dietary Glutamate Reduces Systemic But Not Intestinal Leucine Oxidation In Protein Malnourished Piglets

Abstract

Glutamate (GLU) is a nonessential amino acid that is the major oxidative fuel for the gut. Leucine (LEU), a branched‐chain amino acid (BCAA), is reversibly transaminated into glutamate and further irreversibly oxidized into CO2 in the gut. Our aim was to determine whether dietary GLU can suppress gut BCAA oxidation and increase their systemic availability. Neonatal pigs were enterally fed a low protein diet supplemented with glycine (Control, n=5) or monosodium glutamate (MSG, n=5) for 9 days. Whole‐body LEU kinetics were measured on day 7 and day 9 using either an intravenous (IV) or intragastric (IG) infusion of [1‐13C]‐LEU. We also examined the effect of GLU on LEU oxidation in porcine intestinal epithelial cells (IPEC‐J2). Both in vivo and in vitro studies showed no effect of GLU on LEU oxidation in the gut. However, in pigs fed the MSG vs. Control diet, we found a decrease in CO2 production and increase in plasma LEU and isoleucine concentrations, and a trend toward decreased LEU oxidation during the IV tracer infusion. This suggests that MSG reduced LEU oxidation in peripheral tissues but not during first‐pass intestinal metabolism. We conclude that dietary GLU does not reduce LEU oxidation in the developing piglet gut. Further investigations are warranted to determine the site of dietary MSG effect on whole‐body LEU oxidation. (Funded by the International Glutamate Technical Committee)