Oral and intravenously administered amino acids produce similar effects on muscle protein synthesis in the elderly

Blake B. Rasmussen, R. R. Wolfe, E. Volpi

Research output: Contribution to journalArticlepeer-review

57 Scopus citations


BACKGROUND: Muscle protein synthesis is stimulated in the elderly when amino acid availability is increased. OBJECTIVE: To determine which mode of delivery of amino acids (intravenous vs. oral ingestion) is more effective in stimulating the rate of muscle protein synthesis in elderly subjects. DESIGN: Fourteen elderly subjects were assigned to one of two groups. Following insertion of femoral arterial and venous catheters, subjects were infused with a primed, continuous infusion of L-[ring-2H5] phenylalanine. Blood samples and muscle biopsies were obtained to measure muscle protein fractional synthesis rate (FSR) with the precursor-product model, phenylalanine kinetics across the leg with the three-pool model, and whole body phenylalanine kinetics. Protein metabolism parameters were measured in the basal period, and during the administration of oral amino acids (n=8) or a similar amount of intravenous amino acids (n=6). RESULTS: Enteral and parenteral amino acid administration increased amino acid arterial concentrations and delivery to the leg to a similar extent in both groups. Muscle protein synthesis as measured by both FSR, and the three-pool model, increased during amino acid administration (P < 0.05 vs. basal) in both groups with no differences between groups. Whole body proteolysis did not change with the oral amino acids whereas it increased slightly during parenteral amino acid administration. CONCLUSIONS: Increased amino acid availability stimulates the rate of muscle protein synthesis independent of the route of administration (enteral vs. parenteral).

Original languageEnglish (US)
Pages (from-to)358-362
Number of pages5
JournalJournal of Nutrition, Health and Aging
Issue number6
StatePublished - 2002


  • Aging
  • Amino acids
  • Muscle protein synthesis
  • Stable isotopes

ASJC Scopus subject areas

  • Medicine (miscellaneous)
  • Nutrition and Dietetics
  • Geriatrics and Gerontology


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