Suppression of glycogen consumption during acute exercise by dietary branched-chain amino acids in rats

The effects of a diet supplemented with branched-chain amino acids (BCAA; 4 .8% or 6.2%) on BCAA catabolism and glycogen metabolism in rats were examin ed. Rats were fed a BCAA diet or control diet for 4 wk and part of the rats were subjected to exercise training during the experimental period. Feedin g the BCAA diet increased serum BCAA concentrations and activity of the hep atic branched-chain alpha-keto acid dehydrogenase complex, the rate-limitin g enzyme in the catabolism of BCAA, suggesting that dietary BCAA promotes B CAA catabolism. Although the serum glucose concentration and glycogen conte nts in the liver and gastrocnemius muscle of rested rats were not significa ntly affected by feeding of the BCAA diet, those in rats exhausted by acute exercise were 2-4-fold higher in rats fed the BCAA diet than in rats fed t he control diet. The activity of pyruvate dehydrogenase complex in the live r and gastrocnemius muscle after acute exercise showed reverse trends; the complex activities (especially in liver) tended to be less in the BCAA diet group than in the control diet group. These results suggest that dietary B CAA spares glycogen stores in liver and skeletal muscle during exercise and that the decrease in pyruvate dehydrogenase complex activity in these tiss ues by dietary BCAA is involved in the mechanisms.