American Journal of Clinical Nutrition, Vol 55, 971-975, Copyright © 1992 by The American Society for Clinical Nutrition, Inc

ORIGINAL RESEARCH COMMUNICATIONS

Glycine, leucine, and phenylalanine flux in low-birth-weight infants during parenteral and enteral feeding

LJ Wykes, RO Ball, CE Menendez, DM Ginther and PB Pencharz
Research Institute, Hospital for Sick Children, Toronto, Ontario, Canada.

Kinetics of three amino acids with different sites and characteristics of metabolic regulation were studied in low-birth-weight infants during enteral and parenteral feeding regimens typical of clinical practice. Primed constant infusions of [15N]glycine, L-[1-13C]leucine, and L-[1- 13C]phenylalanine were administered simultaneously by the same route as the feeding, with isotope enrichment measured in urine over 12 h. The effect of feeding regimen was specific to each amino acid (mean +/- SD): glycine flux was lower during parenteral feeding (470 +/- 15 vs 561 +/- 69 mumol.kg-1.h-1, P less than 0.05), leucine flux was unaffected (360 +/- 77 vs 388 +/- 78 mumol.kg-1.h-1), and phenylalanine flux was higher (106 +/- 29 vs 56 +/- 6 mumol.kg-1.h-1, P less than 0.01). Kinetics were influenced by the interaction of several factors, including amino acid intake and routes of feeding and tracer administration. Glycine was most affected by route of feeding and phenylalanine was most affected by intake whereas leucine was little affected. Estimates of whole-body protein turnover calculated from leucine and phenylalanine were different; thus calculations of protein turnover from kinetics of a single amino acid should be interpreted with caution.

This article has been cited by other articles:

				P. B. Darling, M. Dunn, G. S. Gilani, R. O. Ball, and P. B. Pencharz Phenylalanine Kinetics Differ between Formula-Fed and Human Milk-Fed Preterm Infants J. Nutr., October 1, 2004; 134(10): 2540 - 2545. [Abstract] [Full Text] [PDF]

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				P. B Darling, M. Dunn, G. Sarwar, S. Brookes, R. O Ball, and P. B Pencharz Threonine kinetics in preterm infants fed their mothers' milk or formula with various ratios of whey to casein Am. J. Clinical Nutrition, January 1, 1999; 69(1): 105 - 114. [Abstract] [Full Text] [PDF]

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				R. F. P. Bertolo, C. Z. L. Chen, G. Law, P. B. Pencharz, and R. O. Ball Threonine Requirement of Neonatal Piglets Receiving Total Parenteral Nutrition Is Considerably Lower than That of Piglets Receiving an Identical Diet Intragastrically J. Nutr., October 1, 1998; 128(10): 1752 - 1759. [Abstract] [Full Text]