The role of leukocytes in the pathophysiology of skeletal muscle ischemic injury

Neutrophilic leukocytes have been implicated as important mediators of ischemic myocardial injury. We investigated the role of neutrophils in skeletal muscle ischemia/reperfusion injury by using the rat hindlimb ischemia model. We rendered Wistar rats neutropenic by administering 750 rad of whole-body radiation (mean white blood cell count, 300 +/- 50/mm3; 3 days after radiation). In anesthetized rats (10 neutropenic and 10 control), 3 hours of ischemia were induced in one hindlimb by application of a tourniquet to the proximal thigh; the contralateral limb served as an internal, nonischemic control. After 1 hour of reperfusion the gastrocnemius and soleus muscles were excised bilaterally and evaluated for ischemic injury by means of a quantitative spectrophotometric assay of triphenyltetrazolium chloride (TTC) reduction. In control rats the reduction of TTC by ischemic muscle averaged 27.0% +/- 7.3% of that by nonischemic muscle; whereas in neutropenic rats the value for ischemic muscle was 65.4 +/- 11.6% (p less than 0.05). To determine if the contribution of the neutrophils to ischemic injury is due to oxygen-derived free radical formation, an additional 10 animals were infused with 5000 units of super-oxide dismutase and 10,000 units of catalase at the time reperfusion was restored. After treatment with free radical scavengers, TTC reduction by ischemic limbs was 25.5% +/- 7.0% of that by nonischemic limbs and did not differ from that in control animals (p greater than 0.05). The results show a protective effect of neutropenia and suggest a significant role of the white cell in the pathophysiology of ischemic skeletal muscle injury.