Effect of long-term electrical stimulation on vascular supply and fatigue in chronically ischemic muscles.

Fast skeletal muscles of Sprague-Dawley rats [tibialis anterior (TA) and extensor digitorum longus (EDL)] were subjected to ischemia by unilateral ligation of the common iliac artery. In some animals, ischemia was combined with indirect electrical stimulation at 10 Hz either for 3 x 2 h (strenuous activity) or for 7 x 10-min bouts/day (mild activity). After 2 wk, muscle blood flow and fatigue were measured during 5-min isometric supramaximal twitch contractions at 4 Hz. Terminal arteriole diameters were assessed in TA by intravital microscopy at rest and during contractions. Vascular perfusion pressure in the muscles was estimated from measurements in the carotid and saphenous arteries below the site of ligation. Capillary supply was expressed in TA and EDL as capillary-to-fiber ratio on the basis of histochemical staining for capillaries. Strenuous stimulation of ischemic muscles increased their atrophy, failed to restore blood flow, and actually worsened fatigue. In contrast, mild stimulation improved perfusion pressure, increased capillary-to-fiber ratio in the glycolytic part of TA, restored dilatation of terminal arterioles during muscle contractions, and improved blood flow and muscle fatigue so that they were no longer significantly different from control muscles. Thus, an attenuated intermittent protocol may be indicated in the treatment of muscle ischemia.