To quantitate glutamine kinetics in premature infants and determine wh
ether glutamine affects leucine metabolism, 11 very low birth weight (
<1250 g) neonates received 4-h i.v. infusions of L-[H-2(3)]leucine and
L-[C-13(5),]glutamine, along with orogastric infusion of L-[1-C-13]le
ucine and L-[1-C-13]glutamine on the 10th d of life and in the fed sta
te. Patients were receiving parenteral nutrition and were randomized t
o receive either hypocaloric, enteral preterm formula alone (controls;
n = 5), or glutamine (0.2 g . kg(-1). d(-1) on the day of the study)
supplemented formula (GLN; n = 6). The rates of appearance (R(a)) of l
eucine and glutamine, and their rates of splanchnic extraction were de
termined from isotopic enrichments in plasma at steady state. Leucine
release from protein breakdown did not differ between groups (123 +/-
51 versus 162 +/- 94 mu mol . kg(-1)h(-1) in the controls and GLN grou
p, respectively). Glutamine de novo synthesis accounted for >80% of ov
erall glutamine R(a), and was similar in both groups (626 +/- 177 vers
us 525 +/- 86 mu mol . kg(-1). h(-1); NS); 46 +/- 16% and 53 +/- 31% o
f the enteral glutamine underwent first-pass splanchnic extraction in
the controls and GLN group, respectively. These findings indicate that
the pathways of glutamine de novo synthesis and glutamine utilization
in the splanchnic bed are functional in very low birth weight humans
by the 10th d of life. Glutamine supplementation Provided at low doses
on a hypocaloric regimen results in no apparent differences in flux o
f glutamine or leucine.