REGULATION OF GLYCOGEN-SYNTHASE AND PHOSPHORYLASE DURING RECOVERY FROM HIGH-INTENSITY EXERCISE IN THE RAT

The aim of this study was to determine the role of the phosphorylation state of glycogen synthase and glycogen phosphorylase in the regulati on of muscle glycogen repletion in fasted animals recovering from high -intensity exercise. Groups of rats were swum to exhaustion and allowe d to recover for up to 120 min without access to food. Swimming to exh austion caused substantial glycogen breakdown and lactate accumulation in the red, white and mixed gastrocnemius muscles, whereas the glycog en content in the soleus muscle remained stable. During the first 40 m in of recovery, significant repletion of glycogen occurred in all musc les examined except the soleus muscle. At the onset of recovery, the a ctivity ratios and fractional velocities of glycogen synthase in the r ed, white and mixed gastrocnemius muscles were higher than basal, but returned to pre-exercise levels within 20 min after exercise. In contr ast, after exercise the activity ratios of glycogen phosphorylase in t he same muscles were lower than basal, and increased to pre-exercise l evels within 20 min. This pattern of changes in glycogen synthase and phosphorylase activities,never reported before, suggests that the inte grated regulation of the phosphorylation state of both glycogen syntha se and phosphorylase might be involved in the control of glycogen depo sition after high-intensity exercise.