Ischemic preconditioning prevents skeletal muscle tissue injury, but not nerve lesion upon tourniquet-induced ischemia

Background: Prolonged ischemia followed by reperfusion (I/R) of skeletal muscle results in significant tissue injury. Ischemic preconditioning IPC), achieved by brief periods of ischemia before sustained ischemia, has been shown to ameliorate I/R injury in a variety of tissues. We demonstrate that tourniquet hind limb ischemia-induced injury of the muscle benefits from IPC, whereas the peripheral nerve suffers from prolonged ischemia time and mechanical deterioration on IPC. Methods: in anesthetized rats, hind limb ischemia was induced by tourniquet for 3 hours followed by 24 hours of reperfusion. In an additional series of experiments, IPC (three cycles of 10 minutes I/10 minutes R) preceded hind limb ischemia. Sham-operated animals without ischemia served as controls. Skeletal muscle tissue injury was assessed with respect to microcirculation, inflammatory cell response, and cell integrity using intravital fluorescence microscopy, Western blot protein analysis, and tissue histochemistry. Analysis of tactile and thermal allodynia served as indicators for postischemic pain. In addition, motor nerve conduction velocity and transmission electron microscopy allowed assessing postischemic nerve lesion. Results: Tourniquet of the hind limb caused marked perfusion failure, enhanced leukocyte-endothelial cell interaction, and apoptotic cell death. IPC was able to improve microvascular perfusion and to reduce inflammatory cell response. Of interest, apoptotic cell death, assessed by cell nuclear morphology in vivo as well as Western blot and immunohistochemical analysis of caspase-3 cleavage, can be substantially reduced by IPC in tourniquet ischemia of the hind limb. Application of the tourniquet abolished nerve conduction in all animals. Non-IPC-treated animals still showed tactile allodynia, whereas IPC further caused loss of pain sensation and motor function of the postischemic hind limb. Conclusions: High susceptibility of the peripheral nerve to compression-induced ischemic injury disproves IPC in its clinical application for surgical procedures requiring prolonged tourniquet ischemia.