A new method to measure muscle protein synthesis in humans by endogenously introduced d9-leucine and using blood for precursor enrichment determination

Lee Tran, Haley Masters, Lori R. Roust, Christos S. Katsanos

Research output: Contribution to journalArticle

5 Scopus citations

Abstract

Enrichment from the easily accessible blood amino acid pool is commonly used as precursor enrichment to calculate rates of muscle protein fractional synthesis in relevant human studies in lieu of the less accessible muscle fluid amino acid pool. However, the accuracy of this approach depends largely on the extent to which there is low discrepancy in free amino acid enrichment between blood and muscle. Steady-state gradient (i.e., ratio) of amino acid enrichment between blood and muscle fluid in the basal state and in response to amino acid infusion were determined in five healthy subjects, and in association with two separate tracers: d9-leucine, introduced endogenously by the metabolism of d10-leucine (i.e., L-[2,3,3,4,5,5,5,6,6,6-2H10]leucine) infused in blood, and13C6-phenylalanine introduced/infused in blood. The blood-tomuscle fluid amino acid enrichment ratio was lower (P < 0.05) for d9-leucine compared to s13C6-phenylalanine both before (1.5 ± 0.1 vs. 2.5 ± 0.1) and during (1.1 ± 0.1 vs. 1.2 ± 0.1) amino acid infusion. Importantly, the decrease in this ratio in association with the amino acid infusion was considerably less for the d9-leucine than the13C6-phenylalanine (-0.38 ± 0.03 vs. -1.29 ± 0.07; P < 0.05). In conclusion, blood d9-leucine enrichment introduced endogenously by intravenous infusion of d10-leucine provides a closer estimate of the muscle fluid amino acid enrichment, and its associated changes, than blood phenylalanine enrichment to calculate rates of muscle protein synthesis in humans.

Original languageEnglish (US)
Article numbere12479
JournalPhysiological reports
Volume3
Issue number8
DOIs
StatePublished - 2015

Keywords

  • Amino acids
  • Fractional synthesis rate
  • Humans
  • Stable isotope tracer
  • d-leucine

ASJC Scopus subject areas

  • Physiology
  • Physiology (medical)

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