Effect of glutamine on leucine metabolism in humans.
Hankard, R[acute]egis G., Morey W. Haymond, and Dominique Darmaun.
Nemours Children's Clinic, Jacksonville, Florida
APStracts 3:0115E, 1996.
The aim of this study was to determine whether the putative protein
anabolic effect of glutamine: 1) is mediated by increased protein
synthesis or decreased protein breakdown, and 2) is specific to
glutamine. Seven healthy adults were administered 5-h intravenous
infusions of L-[1-14C]leucine in the postabsorptive state while
receiving in a randomized order an enteral infusion of saline on one
day or L-glutamine (800 [mu]mol.kg-1.h-1, equivalent to 0.11 g of
nitrogen per kg) on the other day. Seven additional subjects were
studied using the same protocol except they received isonitrogenous
infusion of glycine. The rates of leucine appearance (RaLEU), an
index of protein degradation, leucine oxidation (OxLEU), and non
oxidative leucine disposal (NOLD), an index of protein synthesis,
were measured using the 14C-specific activity of plasma [alpha]
-ketoisocaproate and the excretion rate of 14CO2 in breath. During
glutamine infusion, plasma glutamine concentration doubled (673 +/-
66 v 1184 +/- 37 [mu]M (p<0.05) whereas RaLEU did not change
(122 +/- 9 v 122 +/- 7 [mu]mol.kg-1.h-1), OxLEU decreased (19 +/- 2 v
11 +/- 1 [mu]mol.kg-1.h-1, p<0.01), and NOLD increased (103 +/-8
v 111+/- 6 [mu]mol.kg-1.h-1, p<0.01). During glycine infusion,
plasma glycine increased 14-fold (268 +/- 62 v 3806 +/- 546 [mu]M
(p<0.01), but in contrast with glutamine, RaLEU (124 +/- 6 v 110
+/- 4 [mu]mol.kg-1.h-1, p=0.02), OxLEU (17 +/- 1 v 14 +/- 1
[mu]mol.kg-1.h-1, p=0.03), and NOLD (106 +/- 5 v 96 +/- 3 [mu]mol.kg
-1.h-1, p<0.05) all decreased. We conclude that glutamine enteral
infusion may exert its protein anabolic effect by increasing protein
synthesis whereas an isonitrogenous amount of glycine merely
decreases protein turnover with only a small anabolic effect
resulting from a greater decrease in proteolysis than protein
synthesis.
Received 20 February 1996; accepted in final form 5 June 1996.
APS Manuscript Number E88-6.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 28 June 96