Oral and intravenously administered amino acids produce similar effects on muscle protein synthesis in the elderly
Rasmussen, B.B.; Wolfe, R.R.; Volpi, E.
Journal of Nutrition Health and Aging 6(6): 358-362
2002
ISSN/ISBN: 1279-7707 PMID: 12459885 Document Number: 542645
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 (12 men, 2 women; mean age: 71+or-1 years) were recruited through the Center on Aging Volunteers Registry of the University of Texas Medical Branch (Texas, USA), and were assigned to one of two groups 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).