title: Protein anabolic responses to a fed steady state in healthy aging.
abstract: BACKGROUND
  Protein anabolism in response to feeding may be impaired with aging. To determine if this could contribute to muscle loss, we studied fed-state metabolic responses in healthy, non-sarcopenic elderly women.
  
  
  METHODS
  Whole-body [(3)H]glucose and protein ([(13)C]leucine) kinetics were measured, and muscle protein fractional synthesis rate ([(2)H(5)]phenylalanine) and signaling events were assessed from vastus lateralis biopsies in eight elderly (73 ± 3 years) and eight young women (24 ± 1 years), using a simulated fed steady-state clamp.
  
  
  RESULTS
  Both groups had similar muscle and lean body mass indices and activity level. During insulin, glucose (8 mmol/L), and amino acid (AA; 2× fasting) infusions, serum insulin was lower in the elderly women and C-peptide increased less. Glucose uptake was stimulated, and production suppressed similarly. Suppression of whole-body protein breakdown was less in the elderly women, leading to lower AA infusion rates, oxidation, and net positive protein balance, but differences were not present when adjusted for serum insulin. Whole-body protein synthesis and muscle protein fractional synthesis rate increased similarly. Similar increases in phosphorylated Akt(Ser473), PRAS40(Thr246), FoxO3a(Thr32), and rpS6(Ser240/244) indicated no alterations in insulin/nutrient signaling with aging.
  
  
  CONCLUSIONS
  Both whole-body and muscle fed-state protein anabolic responses were preserved, as was insulin sensitivity of glucose metabolism, in active, healthy elderly women. This is consistent with other factors such as sedentarity, low protein intake, and concurrent diseases, being responsible for the sarcopenia of aging.
authors: McGill Nutrition and Food Science Centre, and Department of Medicine, Division of Geriatrics, McGill University Health Centre, Montreal, Quebec, Canada.
authors: Stéphanie
authors: S
authors: Chevalier
authors: Eric D B
authors: ED
authors: Goulet
authors: Sergio A
authors: SA
authors: Burgos
authors: Linda J
authors: LJ
authors: Wykes
authors: José A
authors: JA
authors: Morais
mesh_terms: D000328:Adult; D000368:Aged; D000375:Aging / Q000378:metabolism*; D015444:Exercise; D005260:Female; D005947:Glucose / Q000378:metabolism; D006801:Humans; D007333:Insulin Resistance; D007930:Leucine / Q000378:metabolism; D009124:Muscle Proteins / Q000096:biosynthesis; D010766:Phosphorylation; D011506:Proteins / Q000378:metabolism*; D055948:Sarcopenia / Q000209:etiology
chemical_list: D009124:Muscle Proteins; D011506:Proteins; D007930:Leucine; D005947:Glucose