Effects of a soy protein diet on exercise-induced muscle protein catabolism in rats.
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.
Nikawa
Takeshi
T
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
Ikemoto
Madoka
M
Sakai
Takashi
T
Kano
Mihoko
M
Kitano
Takako
T
Kawahara
Tsukasa
T
Teshima
Shigetada
S
Rokutan
Kazuhito
K
Kishi
Kyoichi
K
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
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