Chronic Stimulation of Extensor Digitorum Longus Autografts in Rats.

Free whole muscle autografts do not spontaneously recover all the characteristics of control muscles after degeneration and regeneration of their muscle fibers. Chronic 10 Hz electrical stimulation of normal muscles enhances characteristics not fully restored in grafts. The purpose of this study was to determine the effects of chronic stimulation on the structural and functional characteristics of grafts. The following hypotheses were tested. Compared to non-stimulated nerve-intact grafts, chronic stimulation of nerve-intact grafts would: (1) increase capillarization, (2) increase oxidative capacity, and (3) increase resistance to fatigue. The hypotheses were tested by first performing nerve-intact transplantations on extensor digitorum longus (EDL) muscles in rats. Reinnervation of the grafts occurred 14 days post-transplantation. The grafts were then stimulated chronically 8 hours/day at 10 Hz. After 26 days of electrical stimulation, contractile properties were measured in situ and in vitro and the muscles were prepared for histochemical and biochemical analysis. Measurements included time to peak tension, half relaxation time, twitch tension, maximum tetanic tension, fatigue time, histochemical myofibrillar ATPase and succinate dehydrogenase activities, fiber areas, capillarity, and concentration of cytochrome c. The measurements obtained for stimulated EDL grafts were compared to the same measurements for stimulated EDL muscles, non-stimulated EDL muscles, and non-stimulated EDL grafts. The stimulated grafts demonstrated similar directional changes in contractile properties as the stimulated normal muscles. These changes included increases in contraction and relaxation times, and decreases in mean fiber area and absolute maximum tetanic tension. The non-stimulated grafts had full restoration to control values for concentration of cytochrome c, and number of capillaries/fiber. The number of capillaries/mm('2) and resistance to fatigue surpassed values for control muscles by 42 and 50%, respectively. Compared to non-stimulated grafts, chronically stimulated grafts demonstrated a 64% greater oxidative capacity, 29% greater number of capillaries/fiber, 46% greater number of capillaries/mm('2) and 72% greater resistance to fatigue. The present study indicates that increasing activity in grafted skeletal muscle, by means of chronic 10 Hz stimulation, has beneficial effects in enhancing their oxidative capacity, capillarity, and resistance to fatigue.Ph.D.Animal PhysiologyUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/159158/1/8304466.pd