REPERFUSION INJURY OF POSTISCHEMIC SKELETAL-MUSCLE IS ATTENUATED BY THE 21-AMINOSTEROIDS U-74389F AND U-74500A INDEPENDENT OF IRON-BINDING

Background. Lazaroids (21-aminosteroids) are a novel class of compound s that have been shown to limit experimental ischemic injury of varied causes. The mechanism of action is uncertain but may include scavengi ng of lipid peroxy radicals, iron binding, or direct membrane interact ion. The purpose of these experiments was to evaluate the capacity of the lazaroids U-74500A and U-74389F to modify ischemia/reperfusion inj ury of skeletal muscle in a well-characterized model of high-grade par tial ischemia. Methods. Nonfasted male Sprague-Dawley rats were anesth etized, a tracheostomy tube was placed, and the carotid artery and jug ular vein were cannulated. Animals received heparin (1 unit/gm) and cr ystalloid (I ml/hr) intravenously. The baseline group (n = 6) was allo wed a 30-minute equilibration period, after which resting transmembran e potential (E(m)) was measured in a hindlimb muscle. Muscle biopsy sp ecimen was obtained; conjugated diene and thiobarbituric acid reactive substances were measured as indexes of lipid peroxidation. Spectropho tometric determination of plasma iron and unsaturated iron-binding cap acity were performed (total iron-binding capacity and percent saturati on were calculated). Animals received U-74389F (2 mg/kg, n = 7), U-745 00A (2 mg/kg, n = 6), or vehicle only (0.02 mol/L citrate acid/citrate ; n = 7) intraarterially before infrarenal aortic clamping was perform ed for 120 minutes. An additional group of animals received U-74389F ( 2 mg/kg, n = 7), U-74500A (2 mg/kg, n = 7), or vehicle (n = 11) intraa rterially before infrarenal aortic clamping was performed for 120 minu tes, followed by reperfusion for 30 minutes. Results. Depolarization o f resting E(m) was noted during ischemia, with partial repolarization on reperfusion, which was enhanced by either lazaroid. As expected, ir on delocalization occurred during ischemia and persisted on reperfusio n, with U-74500A effectively binding iron, whereas U-74389 did not. Ve hicle but not the 21-aminosteroids inhibited lipid peroxidation. Concl usions. High-grade partial ischemia of skeletal muscle is associated w ith iron delocalization, which persists on reperfusion. Each lazaroid achieved a similar ''membranoprotective'' effect during reperfusion on ly despite lack of iron binding by U-74389F suggesting a direct intera ction with the cell membrane. These data support the concept that isch emic injury and reperfusion injury occur through fundamentally differe nt mechanisms.