Effect of amino acids and glucose on exercise-induced gut and skeletal muscle proteolysis in dogs

The effect of amino acid and/or glucose administration before acid during e xercise on protein metabolism in visceral tissues and skeletal muscle was e xamined in mongrel dogs. The dogs were subjected to treadmill running (150 minutes at 10 km/h and 12% incline) and intravenously infused with a soluti on containing amino acids and glucose (AAG), amino acids (AA), glucose (G) or saline (S) in randomized order. The infusion was started 60 minutes befo re exercise and continued until the end of the exercise period, An arteriov enous-difference technique was used to estimate both tissue protein degrada tion and synthesis, When S was infused, the release of leucine (Leu) from t he gut and phenylalanine (Phe) from the hindlimb significantly increased du ring exercise, thus indicating that exercise augmented proteolysis in these tissues. The balance of Leu across the gut during exercise demonstrated a net uptake with both AAG and AA, whereas a net release was observed for G a nd S. In addition, Leu uptake in the gut during the last 90 minutes of the exercise period tended to be greater with AAG versus AA (P = .06). Phe bala nce across the hindlimb during the late exercise period showed a significan t release with S, AA, and G, whereas the balance with AAG did not show a si gnificant release. These results suggest that exercise-induced proteolysis in the gut may be reduced by supplementation with AA, and this effect may b e enhanced by concomitant G administration, However, in skeletal muscle, bo th AA and G may be required to prevent net protein degradation during exerc ise. G provided without AA did not achieve net protein synthesis in either tissue. Copyright (C) 1999 by W.B. Saunders Company.