Postischemic skeletal muscle injury: patterns of injury in relation to adequacy of reperfusion

Ischemia-induced skeletal muscle injury was studied in rats subjected to tourniquet hindlimb ischemia for 3, 4, or 5 hr. The extent of injury was evaluated morphologically after 5 or 20 hr of reperfusion by a dye exclusion test using Evans blue/albumin (EBA) and a histochemical stain for calcium, Alizarin red S (ARS). In addition, the distribution of Evans blue in the postischemic muscle served as a means for detecting areas of defect reperfusion--no reflow. The combination of EBA and ARS allowed easy and reproducible quantification of induced injury in adequately reperfused areas. In areas of no reflow none of the markers used were useful. Muscle cells in these areas appeared structurally well preserved even 20 hr after release of the tourniquet and no cytoplasmic calcium accumulation could be demonstrated in muscle cells by staining with ARS. In many of these areas, however, ARS-positive structures were found between muscle cells, distributed in a pattern corresponding to the capillary network. The nature of these structures, constituting a morphological correlate to the no-reflow phenomenon, is unclear. It is concluded that for the proper evaluation of postischemic skeletal muscle injury, a suitable marker allowing estimation of the adequacy of the reperfusion must be used.