Generation of Free Radicals During Cold Injury and Rewarming

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Abstract
Cold injury is often associated with irreversible cell damage. At present, however, the pathophysiology of cold injury is not known. This study examines the mechanism of such injury. New Zealand white rabbits were anesthetized and their femoral artery and vein were exposed. After baseline measurements one hind limb was cooled with a freezing mixture to 0°C, followed by rewarming. The other hind limb served as control. During the experiment blood samples were withdrawn from the femoral artery and vein for the subsequent analysis of creatine kinase (CK), lactate dehydrogenase (LDH), and malonaldehyde (MDA). At the end salicylate was injected through the femoral vein to trap any hydroxyl radical (OH°) formed. Rabbits were immediately sacrificed, and biop sies were withdrawn and frozen at liquid nitrogen temperature for analysis of OH° and high-energy phosphate compounds. The results indicate that local blood flow in the cold-exposed hind limb was reduced significantly, suggesting that cold injury was associated with ischemic insult. CK and LDH increased after cold exposure and increased further during rewarming. MDA formation followed a similar pattern. OH° generated after cooling increased significantly upon rewarming. These results indicate that re warming is associated with an episode of ischemia/reperfusion with simultane ous generation of free radicals, which, at least in part, may be responsible for cellular injury associated with rewarming.