Patterns of glycogen loss in muscle fibers: response to arterial occlusion during exercise

This experiment was designed to determine if glycogen loss in active rat skeletal muscle fibers could be accentuated by periodic occlusion of blood to the muscles without significantly altering the numbers of types of fibers that lose glycogen. We attempted to augment glycogen loss by periodically occluding blood flow to the muscles while the animals ran on a treadmill. An occluder cuff was placed on the right common iliac artery of 10 rats. While the rats ran for 5 min at 26 m . min-1, blood flow to the right hindlimb was completely occluded for 16 +/- 5 (SD) s during every 30 s of the run. Glycogen loss in soleus (S), plantaris (P), and gastrocnemius (G) muscles was determined biochemically and histochemically. Muscles from both the occluded limb (S, P, and the deep red portion of G) and the nonoccluded limb (S and red G) of the runners showed significant glycogen loss compared with the controls. Furthermore, glycogen concentration was significantly lower in S, P, and red G of the occluded limb than in the same muscles of the nonoccluded limb. Significantly greater numbers of fibers within fiber type populations of P and G showed glycogen loss in the occluded limb, indicating that more motor units were recruited during the exercise bout in these muscles. The data suggest a sensitive link between motor unit recruitment and the metabolic condition of the contracting fibers, as the increased number of fibers showing glycogen loss presumably, resulted from fatigue of active units. We conclude that occlusion of blood flow to active muscles is not a feasible means of accentuating glycogen loss in active fibers while maintaining normal patterns of recruitment.