The accumulation of polymorphonuclear leukocytes in post-ischemic skeletal muscle in the rat, measured by quantitating tissue myeloperoxidase.

In the present study we have evaluated the activity of myeloperoxidase (MPO) in ischemic reperfused skeletal muscle of rats, as an index of polymorphonuclear leukocyte (PMNL) accumulation and its time course. A tourniquet model for temporary ischemia was used, in which one hindleg was made ischemic for 1.5, 3 or 5 hours. Muscle biopsies were taken after 12 hours reperfusion from both the injured and the uninjured legs. Controls received anesthesia only. No increase in the MPO levels was observed after 1.5 hours of ischemia followed by 12 hours of reperfusion. With the same reperfusion time and 3 or 5 hours of ischemia, there was a five-fold increase in MPO activity. Prolonging the ischemia from 3 to 5 hours did not cause any further significant MPO increase. With 3 hours of ischemia, biopsies were also taken after 0, 1, 5, 24 and 74 hours reperfusion. The results showed a time dependent increase in MPO activity. A significant increase was first seen after 5 hours reperfusion with the peak at 24 hours. After 74 hours of reperfusion the MPO activity had almost returned to control levels. The uninjured leg had MPO levels similar to those in the control. However, there was a small reduction at 5 and 12 hours of reperfusion. During the ischemic period before reperfusion, the ischemic leg showed a significant decrease in MPO activity. Severe ischemia in skeletal muscle results in a time dependent accumulation of PMNLs during reperfusion, as measured by the changes in MPO activity in the tissue.