title: Whey protein intake after resistance exercise activates mTOR signaling in a dose-dependent manner in human skeletal muscle.
abstract: OBJECTIVE
  Protein ingestion after resistance exercise increases muscle protein synthesis (MPS) in a dose-dependent manner. However, the molecular mechanism(s) for the dose-dependency of MPS remains unclear. This study aimed to determine the dose response of mammalian target of rapamycin (mTOR) signaling in muscle with ingestion of protein after resistance exercise.
  
  
  METHODS
  Fifteen male subjects performed four sets of six unilateral isokinetic concentric knee extensions. Immediately after exercise, eight subjects consumed water only. The other seven subjects, in a randomized-order crossover design, took either a 10 [3.6 g essential amino acids (EAA)] or 20 g (7.1 g EAA) solution of whey protein. Muscle biopsies from the vastus lateralis muscle were taken 30 min before and 1 h after resistance exercise. Phosphorylation of Akt (Ser473), mTOR (Ser2448), 4E-BP1 (Thr37/46), and S6K1 (Thr389) was measured by western blotting.
  
  
  RESULTS
  Concentric knee extension exercise alone did not increase phosphorylation of Akt and mTOR 1 h after exercise, but ingesting protein after exercise significantly increased the phosphorylation of Akt and mTOR in a dose-dependent manner (P < 0.05). 4E-BP1 phosphorylation significantly decreased after resistance exercise (P < 0.05), but subjects who took 10 or 20 g of protein after exercise showed increased 4E-BP1 from post-exercise dephosphorylation (P < 0.05). S6K1 phosphorylation significantly increased after resistance exercise (P < 0.05), and 20 g of protein further increased S6K1 phosphorylation compared with ingestion of 10 g (P < 0.05).
  
  
  CONCLUSIONS
  These findings suggest that whey protein intake after resistance exercise activates mTOR signaling in a dose-dependent manner in untrained men.
authors.affiliation: Institute of Health and Sports Science & Medicine, Juntendo University, 1-1 Hiragagakuendai, Inzai, Chiba, 270-1695, Japan.
authors.forename: Ryo
authors.initials: R
authors.lastname: Kakigi
authors.forename: Toshinori
authors.initials: T
authors.lastname: Yoshihara
authors.forename: Hayao
authors.initials: H
authors.lastname: Ozaki
authors.forename: Yuji
authors.initials: Y
authors.lastname: Ogura
authors.forename: Noriko
authors.initials: N
authors.lastname: Ichinoseki-Sekine
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Kobayashi
authors.forename: Hisashi
authors.initials: H
authors.lastname: Naito
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D000284:Administration, Oral; D000601:Amino Acids, Essential / Q000378:metabolism; D018797:Cell Cycle Proteins; D018592:Cross-Over Studies; D004305:Dose-Response Relationship, Drug; D006801:Humans; D007717:Knee / Q000502:physiology; D008297:Male; D008894:Milk Proteins / Q000008:administration & dosage / Q000494:pharmacology*; D018482:Muscle, Skeletal / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D055070:Resistance Training; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism*; D000067816:Whey Proteins; D055815:Young Adult
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D000601:Amino Acids, Essential; D018797:Cell Cycle Proteins; C087000:EIF4EBP1 protein, human; D008894:Milk Proteins; D010750:Phosphoproteins; D000067816:Whey Proteins; D051057:Proto-Oncogene Proteins c-akt; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D058570:TOR Serine-Threonine Kinases; C448901:ribosomal protein S6 kinase, 70kD, polypeptide 1