title: Differential stimulation of muscle protein synthesis in elderly humans following isocaloric ingestion of amino acids or whey protein.
abstract: To counteract the debilitating progression of sarcopenia, a protein supplement should provide an energetically efficient anabolic stimulus. We quantified net muscle protein synthesis in healthy elderly individuals (65-79 yrs) following ingestion of an isocaloric intact whey protein supplement (WY; n=8) or an essential amino acid supplement (EAA; n=7). Femoral arterio-venous blood samples and vastus lateralis muscle biopsy samples were obtained during a primed, constant infusion of L-[ring-2H5]phenylalanine. Net phenylalanine uptake and mixed muscle fractional synthetic rate (FSR) were calculated during the post-absorptive period and for 3.5 h following ingestion of 15 g EAA or 15 g whey. After accounting for the residual increase in the intracellular phenylalanine pool, net post-prandial phenylalanine uptake was 53.4+/-9.7 mg phe leg-1 (EAA) and 21.7+/-4.6 mg phe leg-1 (WY), (P<0.05). Postabsorptive FSR values were 0.056+/-0.004% h-1 (EAA) and 0.049+/-0.006% h-1 (WY), (P>0.05). Both supplements stimulated FSR (P<0.05), but the increase was greatest in the EAA group with values of 0.088+/-0.011% h-1 (EAA) and 0.066+/-0.004% h-1 (WY), (P<0.05). While both EAA and WY supplements stimulated muscle protein synthesis, EAAs may provide a more energetically efficient nutritional supplement for elderly individuals.
authors.affiliation: Department of Surgery, The University of Texas Medical Branch, and Shriners Hospitals for Children, Galveston, Texas 77550, USA. djpaddon@utmb.edu
authors.forename: Douglas
authors.initials: D
authors.lastname: Paddon-Jones
authors.forename: Melinda
authors.initials: M
authors.lastname: Sheffield-Moore
authors.forename: Christos S
authors.initials: CS
authors.lastname: Katsanos
authors.forename: Xiao-Jun
authors.initials: XJ
authors.lastname: Zhang
authors.forename: Robert R
authors.initials: RR
authors.lastname: Wolfe
mesh_terms: D000284:Administration, Oral; D000368:Aged; D000375:Aging / Q000502:physiology*; D000596:Amino Acids / Q000008:administration & dosage* / Q000032:analysis / Q000378:metabolism; D000704:Analysis of Variance; D005260:Female; D006801:Humans; D007866:Leg / Q000098:blood supply; D008297:Male; D008894:Milk Proteins / Q000008:administration & dosage* / Q000737:chemistry / Q000378:metabolism; D009124:Muscle Proteins / Q000096:biosynthesis*; D010649:Phenylalanine / Q000032:analysis / Q000097:blood; D012039:Regional Blood Flow; D000067816:Whey Proteins
chemical_list: D000596:Amino Acids; D008894:Milk Proteins; D009124:Muscle Proteins; D000067816:Whey Proteins; D010649:Phenylalanine