Journal
AMERICAN JOURNAL OF PHYSIOLOGY-ENDOCRINOLOGY AND METABOLISM
Volume 290, Issue 4, Pages E622-E630Publisher
AMER PHYSIOLOGICAL SOC
DOI: 10.1152/ajpendo.00274.2005
Keywords
stable isotope tracers; glutamine metabolism; protein metabolism; very low birth weight; neonates
Categories
Funding
- NCRR NIH HHS [RR-00080, M01 RR000080] Funding Source: Medline
- NICHD NIH HHS [R01-HD-042154, R01 HD042154] Funding Source: Medline
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Glutamine may be a conditionally essential amino acid in low-birth-weight ( LBW) preterm neonates. Exogenously administered amino acids, by providing anaplerotic carbon into the tricarboxylic acid cycle, could result in greater cataplerotic efflux and glutamine de novo synthesis. The effect of dose and duration of amino acid infusion on glutamine and nitrogen (N) kinetics was examined in LBW infants in the period immediately after birth. Preterm neonates ( < 32 weeks gestation, birth weights 809 1,755 g) were randomized to initially receive either 480 or 960 mu mol . kg(-1) . h(-1) of an intravenous amino acid solution for 19 - 24 hours, followed by a higher or lower amino acid load for either 5 h or 24 h. Glutamine de novo synthesis, leucine N, phenylalanine, and urea kinetics were determined using stable isotopic tracers. An increase in amino acid infusion from 480 to 960 mu mol . kg(-1) . h(-1) for 5 h resulted in decreased glutamine de novo synthesis in every neonate (384.4 +/- 38.0 to 368.9 +/- 38.2 mu mol . kg(-1) . h(-1), P < 0.01) and a lower whole body rate of proteolysis ( P < 0.001) and urea synthesis ( P < 0.001). However, when the increased amino acid infusion was extended for 24 h, glutamine de novo synthesis increased (369.7 +/- 92.6 to 483.4 +/- 97.5 mu mol . kg(-1) . h(-1), P < 0.001), whole body rate of proteolysis did not change, and urea production increased. Decreasing the amino acid load resulted in a decrease in glutamine rate of appearance (R-a) and leucine N R-a, but had no effect on phenylalanine R-a. Acutely stressed LBW infants responded to an increase in amino acid load by transiently suppressing whole body rate of glutamine synthesis, proteolysis, and oxidation of protein. The mechanisms of this transient effect on whole body protein/nitrogen metabolism remain unknown.
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