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


METHODS
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).
Rasmussen
B B
BB
University of Southern California, Department of Kinesiology, University Park Campus, 3560 Watt Way, PED 107, Los Angeles, CA 90089-0652, USA. blakeras@usc.edu
Wolfe
R R
RR
Volpi
E
E
D000284:Administration, Oral; D000368:Aged; D000596:Amino Acids / Q000008:administration & dosage* / Q000493:pharmacokinetics; D001682:Biological Availability; D001692:Biological Transport; D001706:Biopsy; D002408:Catheters, Indwelling; D004750:Enteral Nutrition; D005260:Female; D006801:Humans; D007262:Infusions, Intravenous; D008297:Male; D009124:Muscle Proteins / Q000096:biosynthesis*; D018482:Muscle, Skeletal / Q000378:metabolism*; D010288:Parenteral Nutrition; D010649:Phenylalanine / Q000008:administration & dosage / Q000493:pharmacokinetics
D000596:Amino Acids; D009124:Muscle Proteins; D010649:Phenylalanine