THE EFFECT OF ISCHEMIC PRECONDITIONING ON THE RECOVERY OF SKELETAL-MUSCLE FOLLOWING TOURNIQUET ISCHEMIA

It has been well documented that ischemic preconditioning limits ische mic-reperfusion injury in cardiac muscle, but the ability of ischemic preconditioning to limit skeletal muscle injury is less clear. Previou s reports have emphasized the beneficial effects of ischemic precondit ioning on skeletal muscle structure and capillary perfusion but have n ot evaluated muscle function. We investigated the morphologic and func tional consequences of ischemic preconditioning, followed by a 2-hour period of tourniquet ischemia on muscles in the rat hindlimb. The 2-ho ur ischemia was imposed without preconditioning, or was preceded by th ree brief (10 minutes on/10 minutes off) preischemic conditioning inte rvals. We compared muscle morphology, isometric contractile function, and muscle fatigue proper ties in predominantly fast-twitch, tibialis anterior muscles 3 (n = 8) and 7 (n = 8) days after ischemia-reperfusi on. Two hours of ischemia, followed by reperfusion, results in a 20 pe rcent reduction of muscle mass (p < 0.05) and a 33 percent reduction i n tetanic tension (p < 0.05) when compared with controls (n = 8) at 3 days. The same protocol, when preceded by ischemic preconditioning, re sults in similar decreases in muscle mass and contractile function. Ne uromuscular transmission was also impaired in both ischemic groups 7 d ays after ischemia. Nerve-evoked maximum tetanic tension was 69 percen t of the tension produced by direct muscle stimulation in the ischemia group and 65 percent of direct tension in the ischemic preconditionin g/ischemia group. In summary, ischemic preconditioning, using the same protocol reported to be effective in limiting infarct size in porcine muscle, had no significant benefit in limiting injury or improving re covery in the ischemic rat tibialis anterior. The value of ischemic pr econditioning in reducing imposed ischemic-repel fusion-induced functi onal deficits in skeletal muscle remains to be demonstrated.