Muscle blood flow and fiber activity in partially curarized rats during exercise

We previously reported that low doses of d-tubocurarine attenuated glycogen loss in red muscles of rats during treadmill walking but that the initial hyperemia in the muscles was normal. The present studies were performed to 1) determine with electromyography (EMG) whether red muscle fiber activity is reduced in walking, curarized rats and 2) study muscle blood flow and glycogen loss during running with different doses of curare (dose response). At 0.5 min of treadmill walking (15 m/min), integrated EMG in vastus intermedius (VI) muscle was reduced by an average of 18% in curarized (60 micrograms/kg) rats, although blood flow (measured with microspheres) was the same as in saline control rats. Comparison of blood flows and glycogen loss in quadriceps muscles at 1 min of treadmill running (30 m/min) with different curare doses (20-60 micrograms/kg) demonstrated that red muscle glycogen loss was inversely related to curare dose but that blood flows in the same muscles were unaffected by curare. These findings provide support for our previous conclusion that at the initiation of low to moderate treadmill exercise, red muscle blood flow is not proportional to the activity or metabolism of the muscle fibers.