title: Effects of a soy protein diet on exercise-induced muscle protein catabolism in rats.
abstract: OBJECTIVE
  We examined effects of dietary soy protein isolate on muscle calpain activity and myosin heavy chain (MHC) degradation in rats performing an acute running exercise.
  
  
  METHODS
  In rats fed a 20% casein diet, the treadmill running exercise, fixed at 80 kg/m, transiently increased calpain activity in gastrocnemius muscles in parallel with the release of creatine kinase into plasma. The fixed running also caused an accumulation of immunoreactive degradation fragments of MHC in the muscle. Feeding a 20% soy protein isolate diet as opposed to the control casein diet to rats significantly suppressed the running-induced activation of mu- and m-calpains, fragmentation of MHC, and release of creatine kinase into plasma (P < 0.05).
  
  
  RESULTS
  Rats fed the soy protein isolate diet had significantly higher calpastatin activity in gastrocnemius muscle than did rats fed the casein diet (P < 0.05), indicating that this increase inhibits the exercise-induced autoactivation of calpain. Activities of proteasome, cathepsin B + L, and antioxidant enzymes and the levels of glutathione and thiobarbituric acid-reactive substances in the muscle did not differ between the diet groups at the end of the exercise.
  
  
  CONCLUSIONS
  Our results suggest that diets containing soy protein prevent exercise-induced protein degradation in skeletal muscle, possibly through inhibiting the calpain-mediated proteolysis.
authors.affiliation: Department of Nutrition, School of Medicine, The University of Tokushima, 3-18-15 Kuramoto-cho, Tokushima 770-8503, Japan. nikawa@nutr.med.tokushima-u.ac.jp
authors.forename: Takeshi
authors.initials: T
authors.lastname: Nikawa
authors.forename: Madoka
authors.initials: M
authors.lastname: Ikemoto
authors.forename: Takashi
authors.initials: T
authors.lastname: Sakai
authors.forename: Mihoko
authors.initials: M
authors.lastname: Kano
authors.forename: Takako
authors.initials: T
authors.lastname: Kitano
authors.forename: Tsukasa
authors.initials: T
authors.lastname: Kawahara
authors.forename: Shigetada
authors.initials: S
authors.lastname: Teshima
authors.forename: Kazuhito
authors.initials: K
authors.lastname: Rokutan
authors.forename: Kyoichi
authors.initials: K
authors.lastname: Kishi
mesh_terms: D000818:Animals; D002135:Calcium-Binding Proteins / Q000378:metabolism; D002154:Calpain / Q000037:antagonists & inhibitors / Q000378:metabolism*; D003402:Creatine Kinase / Q000097:blood / Q000378:metabolism; D004789:Enzyme Activation / Q000502:physiology; D008054:Lipid Peroxides / Q000378:metabolism; D008297:Male; D009124:Muscle Proteins / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000201:enzymology / Q000378:metabolism; D018995:Myosin Heavy Chains / Q000378:metabolism*; D010084:Oxidation-Reduction; D010805:Physical Conditioning, Animal / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D030262:Soybean Proteins / Q000008:administration & dosage* / Q000378:metabolism; D017392:Thiobarbituric Acid Reactive Substances / Q000378:metabolism; D013997:Time Factors
chemical_list: D002135:Calcium-Binding Proteins; D008054:Lipid Peroxides; D009124:Muscle Proteins; D030262:Soybean Proteins; D017392:Thiobarbituric Acid Reactive Substances; C033668:calpastatin; D003402:Creatine Kinase; D002154:Calpain; D018995:Myosin Heavy Chains