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Ischemia: Profile of an enemy
Ischemia: Profile of an enemy Reperfusion injury of skeletal muscle Malcolm O. Perry, M.D., and Gary Fantini, M.D., New York, N.Y. Recent experimental studies of temporary skeletal muscle ischemia in dogs showed that progressive deterioration in cell membrane electrical potentials (Em) occurred after partial but not total ischemia. With intracellular adenosine triphosphate concentration within the normal range, cell membrane damage by oxygen-derived free radicals was considered. In rats subjected to 60 minutes of infrarenal aortic occlusion, intra-arterial superoxide dismutase infused during removal of the aortic clamp prevented the continued decrease in Em. These data suggest that oxygen-derived free radicals may be mediators of reperfusion injury of ceU membranes. (J VASe SUP-G 1987;6:231-4.)
Recent studies suggest that partial ischemia, even for short periods of time, can cause cell damage. *s This injury may not be apparent when only the overall activity of the organ system is examined, although numerous clinical examples ofpostischemic problems are seen. Limb swelling after a simple femoropopliteal bypass graft occurs even without venous or lymphatic obstruction and usually only after a successful bypass. In contrast, 2 hours of tourniquet ischemia in a relatively asanguineous leg causes only inconsistent swelling. After renal artery repairs, temporary tubular dysfunction is common; after carotid endarterectomy, usually accompanied only by short periods of partial ischemia, hemodynamic instability may occur. Since tissue necrosis is usually not present, these aberrations may be the result of the physiologic response to ischemia rather than of the ischemia itself. 4'5 Other clinical studies suggest that partial ischemia can damage skeletal muscle. Eldof, Neglan, and Thompson I reported that temporary aortic occlusion in patients undergoing vascular surgery caused metabolic changes in the muscles of the legs, which lasted for at least 16 hours. The effects of partial and total ischemia on canine skeletal muscle were examined in two sets of experiments by us. 2 The hind limbs of dogs were subjected to 3 hours of partial ischemia with a mean peffusion From the Department of Surgery, Division of Vascular Surgery, The New York Hospital--Comell Medical Center. Presented at the Eleventh Annual Meeting of the Southern Association for Vascular Surgery, Scottsdale, Ariz., Jan. 28-31, 1987. Supported in part by National Institutes of Health grant Nos. 5R01 HL 23623-03 and GM 23000. Reprint requests: Malcolm O. Perry, M.D., 1300 York Ave., New York, NY 10021.
pressure of 50 m m Hg and then observed for 3 hours during reperfusion. Measurements of transmembrane electrical potentials (Em) and changes in the concentration of intraceUular high-energy phosphate compounds were used to detect damage. Significant changes in membrane potentials occurred without depletion of intracellular adenosine triphosphate (ATP); these alterations persisted during the 3 hours of reperfusion. These studies clearly showed disturbances in cell membrane function induced by partial ischemia. In a second experiment in 13 dogs we subjected one hind leg to tourniquet ischernia for 3 hours and then observed the leg for 3 hours of reperfusion. Simultaneously, the opposite leg was exposed to 3 hours of partial ischemia (mean arterial blood pressure of 50 torr) and was also observed for 3 hours of repeffusion. The Em deteriorated in both legs during ischemia but promptly returned toward normal values after the tourniquet was released. In contrast, the Em in the limb with partial ischemia continued to deteriorate during reperfusion, despite adequate levels ofintracellular ATP. Membrane damage without significant depression of the intracellular energy system suggested that toxic agents such as oxygen-derived free radicals might be involved.6 There are numerous studies in the literature demonstrating the deleterious effects of oxygen-derived free radicals associated with intestinal and myocardial ischemia, organ transplantation (especially kidney and pancreas), and circulatory shock. T M In many of these experimental models free radical scavengers have been shown to reduce or prevent cell injury, limit increases in capillary and cell permeability, and alter the extent and volume of necrosis produced by ischemia, n'12 Since it has been shown that free radical 231
Journal of VASCULAR SURGERY
232 Perry and Fantini
Table I. Measurement of membrane electrical potentials and adenosine triphosphate levels in control rats (N = 7)
Control Ischemia Reperfusion
Em
ATP
(mv)
(uM/gm wet msue)
93.0 -+ 0.8 74.1 -+ 0.7* 75.7 - 1.0*
5.6 -+ 0.2 5.1 -+ 0.5 5.8 -4- 0.3
*p < 0.05 vs. control.
scavengers such as mannitol, superoxide dismutase (SOD), and catalase are capable of protecting ischemic cardiac muscle during reperfusion, a third experiment was designed to determine whether administration of SOD could prevent skeletal muscle cell injury after temporary partial ischemia. MATERIAL AND METHODS Fourteen nonfasted female Sprague-Dawley rats weighing from 300 to 400 gm were anesthetized with pentobarbital and placed on a warming blanket. A tracheostomy tube was inserted and the rats were permitted to breathe room air. Carotid arterial canhulas were inserted into the aortic arch to monitor systemic blood pressure and obtain samples of blood to measure pH and blood gas tensions. Hind limb adductor muscles were exposed through a small incision and modified Ling-Gerard microelectrodes were used to measure the resting Em as previously reported? '6 An open biopsy specimen of an adjacent muscle was taken by freeze-clamping and the tissue sample was analyzed for concentrations of ATP and creatine phosphate by enzymatic methods previously described, z'6 The abdominal aorta was exposed through a midline incision and after full heparinization it was occluded with a vascular clamp just below the renal arteries. After 60 minutes of aortic occlusion, Ems were measured and muscle samples were obtained for analysis. As the aortic clamp was removed, seven rats received by intra-aortic injection 6000 units of bovine liver SOD suspended in 2 ml of 5% dextrose in water, and seven control animals received 2 ml of a dilute heparin solution (100 units heparin/10 ml normal saline solution). After 30 minutes of reperfusion of the hind limbs, Em measurements and muscle biopsies were repeated on a contralateral hind limb adductor muscle. At the conclusion of the experiment the animals were killed by the administration of an overdose of barbiturate. The data were analyzed by standard statistical methods with analysis of variance and the NewmanKeuls test used for multiple comparisons of means.
Table II. Measurement of membrane electrical potentials and adenosine triphosphate levels in rats receiving superoxide dismutase (N = 7)
Control Ischemia Reperfusion (with SOD)
Em (mV)
A TP (la~llgm wet tissue)
94.4 + 0.7 76.6 _+ 2.8* 88.4 _+ 2.8t
7.3 + 0.1 6.0 _+ 0.7 7.1 -+ 0.2
*p < 0.05 vs. control. t p < 0.05 vs. ischemia.
The results are expressed as mean + the standard crror.
Animal care complied with the "Principles of Laboratory Animal Care" and the "Guide for the Care and Use of Laboratory Animals" (NIH Publication No. 80-23, revised 1978). RESULTS As can be seen in Table I, during the period of ischemia in the control rats there was marked deterioration of the Era, which failed to recover during reperfusion. Throughout the time of this experiment, intracellular levels of ATP remained within a normal range.
In Table II it is seen that the administration of SOD prevented the progressive deterioration of Ems during the reperfusion period. In contrast to the control studies, the Em returned to near normal levels immediately after reperfusion in those animals that received SOD just as the aortic clamp was removed. DISCUSSION The Em is generated by an ATP-dependent pump that moves sodium and potassium against their electrochemical gradients. The Em is determined by the magnitude of these gradients and the different permeabilities of the membrane to sodium and potassium. A decrease in the Em can result from a change in the gradients or a change in the ion permeability of the cell membrane. These studies clearly showed alterations in cell membrane function, changes that continued into the reperfusion period after partial ischemia, but not after total ischemia. The deterioration of the Em apparently is not related to sodium-potassium pump failure from lack of fuel because ATP levels remained adequate. Moreover, the membrane damage is not caused by excessive lactate since levels of this metab-
Volume 6 Number 3 September 1987
olite also immediately returned to normal with restoration of blood flow. s'6 Although the damage to the cell membrane could be the result of some other mechanism, the evidence strongly incriminates oxygen-derived free radicals. Other possibilities exist; for instance, studies of perfused cardiac muscle have demonstrated that when calcium is removed from the perfusate and then reintroduced, cellular damage results. This has been called the "calcium paradox. "~3 A similar situation may exist during partial skeletal muscle ischemia; the primary source of superoxide in reoxygenated cardiac muscle appears to be the enzyme xanthine oxidase, released during ischemia by a calcium-triggered proteolytic attack on xanthine dehydrogenase.14 The clinically observed resistance of skeletal muscle to ischemic injury, relative to other tissues, has been thought to occur because skeletal muscle xanthine dehydrogenase might not convert with nonperfusion. H However, many of these studies were performed in experiments with total ischemia; as the preceding data suggest, there apparently is more likelihood of dysfunction after partial ischemia than after total ischemia, at least within the time frame of 3 hours or less. is In some of the experimental models free radical scavengers have been shown to reduce or prevent cell injury, and recent reports suggest that with total ischemia muscle necrosis can be reduced by the administration of free radical scavengers. H,~4There is evidence that if arterial occlusion is complete, other mechanisms not dependent on free radical generation become the dominant factor, and then pretreatment with free radical scavengers fails to prevent ischemic damage. Moreover, at least in the intestine, the dominant mechanism of injury appears to change when partial ischemia is progressing to complete ischemia, but in cardiac muscle complete ischemia appears to be primarily a worse case of partial ischemia.7 Ninety-eight percent of molecular oxygen is completely reduced to water in the process of respiration; the other 2% can turn into potentially toxic free radicals. It appears that if anything less than complete full reduction of oxygen to water occurs, intermediate substances will be generated, and they must be dealt with in some way. 7'H The major source of superoxide in postischemic tissues appears to be the enzyme xanthine oxidase, which is widely distributed in the body. The enzyme is synthesized as xanthine dehydrogenase (type D); this accounts for about 90% of the total activity in healthy tissue. The conversion of xanthine dehydrogenase to xanthine oxidase (type O) begins when the
Ischemia: Reperfusion injury of skeletal muscle 233
decrease in blood flow to the tissue limits the availability of ATP. As the cell energy charge drops, it is no longer able to maintain a proper ion gradient across its membrane. This precipitates a redistribution of calcium and leads to increased amounts of adenosine monophosphate (AMP). The AMP is catabolized to adenosine, inosine, and hypoxanthine. Therefore, a new enzyme activity appears along with hypoxanthine, one of its two required substrates. 1~ The remaining substrate, molecular oxygen, needed for the generation of type O activity, is supplied during the reperfusion of the tissues, and with it comes a burst of superoxide radicals. Perhaps in the partial ischemia model this activity is present during the period of ischemia and then is accentuated further with reperfusion, as suggested by the progressive deterioration of the Em. Although other scavengers of oxygen-derived free radicals may be equally or more effective than SOD in protecting skeletal muscle from ischemic damage, SOD clearly offered some benefit in this clinically relevant model of temporary abdominal aortic occlusion. The toxic hydroxyl radical, known to cause lipid peroxidation of the cell membrane, is susceptible to neutralization by the administration of mannitol and other scavengers. In experimental models studying ischemic cardiac and skeletal muscle, pretreatment with mannitol has been shown to be of benefit; perhaps the mechanism of its action does not reside in its osmotic activity but rather in its ability to act as a scavenger of these toxic agents. ~6The selective administration of agents that block specific radicals may permit the identification of those scavengers that have clinical usefulness in preventing ischemic damage after temporary arterial occlusion. REFERENCES
1. Eldof B, Neglan P, Thompson D. Temporary incomplete ischemia of the legs induced by aortic clamping in man. Ann Surg 1980;93:89-98. 2. Perry MO, Shires GT III, Albert SA. Cellular changes with graded limb ischemia and reperfusion. J VASe StJrt¢; 1984; 1:536-40. 3. Bulldey GB. The role of oxygen free radicals in human disease processes. Surgery 1982;94:407-11. 4. Fischer EG, Ames A. Studies on mechanisms of impairment of cerebral circulation following ischemia: effect of hemodilution and perfusion pressure. Stroke 1972;3:538-46. 5. White BC, Wiegenstein JG, Winegar CD. Brain ischemic anoxia. Mechanisms of injury. JAMA 1984;251:1586-90. 6. Roberts JP, Perry MO, Hariri RJ, Shires GT. Incomplete recovery of muscle cell function following partial but not complete ischemia. Circ Shock 1985;17:253-8. 7. McCord JM. Oxygen-derived free radicals in postischemic tissue injury. N Engl J Med 1985;312:159-63. 8. Parks DA, Bulkley GB, Granger DN. Role of oxygen-derived
234
9.
10. 11. 12. 13.
Journal of VASCULAR SURGERY
Perryand Fantini
free radicals in digestive tract diseases. Surgery 1983;94: 415-21. 8anfey H, Bulkley GB, Cameron JL. The pathogenesis of acute pancreatitis. The source and role of oxygen-derived free radicals in three different experimental models. Ann Surg 1985;201:633-9. Parks DA, Bulkley GB, Granger DN. Role of oxygen free radicals in shock, ischemia, and organ preservation. Surgery 1983;94:428-32. McCord JM. Defense against free radicals has therapeutic implications. JAMA 1984;251:2187-92. Buchbinder D, Karmody AM, Leather RP, Shah DM. Hypertonic mannitol. Arch Surg 1981;8:8091-7. Zimmerman ANE, Daenes W, Halsman WC, Snyder ],
Wisse E, Durrer D. Morphological changes of heart muscle caused by successive perfusion of calcium-free or calciumcontaining solutions (calcium paradox). Cardiovasc Res 1967;1:201-9. 14. Gardner TJ, Stewart JR, Casale AS, Downey JM, Chambers DE. Reduction of myocardial ischemia injury with oxygenderived free radical scavengers. Surgery 1983;94:423-7. 15. Haljamae H, Enge E. Human skeletal muscle energy metabolism during and after complete tourniquet ischemia. Ann Surg 1975;183:9-16. 16. WiUerson JT, Powell WJ, Guiny TE. Improvement in myocardial function and coronary blood flow in ischemic myocardium after mannitol. J Clin Invest 1972;11:2981-94.
B O U N D VOLUMES AV.AH.ABLE TO SUBSCR/BERS Bound volumes of the JOURNAL OF VASCULAg SURGERY for 1987 are available to subscribers only. They may be purchased from the publisher at a cost of $44.00 ($58.00 international) for Vol. 5 (January to June) and Vol. 6 (July to December). Price includes shipping charges. Each bound volume contains a subject and author index, and all advertising is removed. Copies are shipped within 60 days after publication of the last issue in the volume. The binding is durable buckram with the journal name, volume number, and year stamped in gold on the spine. Payment must accompany all orders. Contact Circulation Fulfillment, The C. V. Mosby Company, 11830 Westline Industrial Drive, St. Louis, MO 63146, USA. In the United States call toll free: (800)325-4177, ext. 351. In Missouri call collect: (314)872-8370, ext. 351. Subscriptions must be in force to qualify. Bound volumes are not available in place of a regular JOURNAL subscription.
Recent studies suggest that partial ischemia, even for short periods of time, can cause cell damage. *s This injury may not be apparent when only the overall activity of the organ system is examined, although numerous clinical examples ofpostischemic problems are seen. Limb swelling after a simple femoropopliteal bypass graft occurs even without venous or lymphatic obstruction and usually only after a successful bypass. In contrast, 2 hours of tourniquet ischemia in a relatively asanguineous leg causes only inconsistent swelling. After renal artery repairs, temporary tubular dysfunction is common; after carotid endarterectomy, usually accompanied only by short periods of partial ischemia, hemodynamic instability may occur. Since tissue necrosis is usually not present, these aberrations may be the result of the physiologic response to ischemia rather than of the ischemia itself. 4'5 Other clinical studies suggest that partial ischemia can damage skeletal muscle. Eldof, Neglan, and Thompson I reported that temporary aortic occlusion in patients undergoing vascular surgery caused metabolic changes in the muscles of the legs, which lasted for at least 16 hours. The effects of partial and total ischemia on canine skeletal muscle were examined in two sets of experiments by us. 2 The hind limbs of dogs were subjected to 3 hours of partial ischemia with a mean peffusion From the Department of Surgery, Division of Vascular Surgery, The New York Hospital--Comell Medical Center. Presented at the Eleventh Annual Meeting of the Southern Association for Vascular Surgery, Scottsdale, Ariz., Jan. 28-31, 1987. Supported in part by National Institutes of Health grant Nos. 5R01 HL 23623-03 and GM 23000. Reprint requests: Malcolm O. Perry, M.D., 1300 York Ave., New York, NY 10021.
pressure of 50 m m Hg and then observed for 3 hours during reperfusion. Measurements of transmembrane electrical potentials (Em) and changes in the concentration of intraceUular high-energy phosphate compounds were used to detect damage. Significant changes in membrane potentials occurred without depletion of intracellular adenosine triphosphate (ATP); these alterations persisted during the 3 hours of reperfusion. These studies clearly showed disturbances in cell membrane function induced by partial ischemia. In a second experiment in 13 dogs we subjected one hind leg to tourniquet ischernia for 3 hours and then observed the leg for 3 hours of reperfusion. Simultaneously, the opposite leg was exposed to 3 hours of partial ischemia (mean arterial blood pressure of 50 torr) and was also observed for 3 hours of repeffusion. The Em deteriorated in both legs during ischemia but promptly returned toward normal values after the tourniquet was released. In contrast, the Em in the limb with partial ischemia continued to deteriorate during reperfusion, despite adequate levels ofintracellular ATP. Membrane damage without significant depression of the intracellular energy system suggested that toxic agents such as oxygen-derived free radicals might be involved.6 There are numerous studies in the literature demonstrating the deleterious effects of oxygen-derived free radicals associated with intestinal and myocardial ischemia, organ transplantation (especially kidney and pancreas), and circulatory shock. T M In many of these experimental models free radical scavengers have been shown to reduce or prevent cell injury, limit increases in capillary and cell permeability, and alter the extent and volume of necrosis produced by ischemia, n'12 Since it has been shown that free radical 231
Journal of VASCULAR SURGERY
232 Perry and Fantini
Table I. Measurement of membrane electrical potentials and adenosine triphosphate levels in control rats (N = 7)
Control Ischemia Reperfusion
Em
ATP
(mv)
(uM/gm wet msue)
93.0 -+ 0.8 74.1 -+ 0.7* 75.7 - 1.0*
5.6 -+ 0.2 5.1 -+ 0.5 5.8 -4- 0.3
*p < 0.05 vs. control.
scavengers such as mannitol, superoxide dismutase (SOD), and catalase are capable of protecting ischemic cardiac muscle during reperfusion, a third experiment was designed to determine whether administration of SOD could prevent skeletal muscle cell injury after temporary partial ischemia. MATERIAL AND METHODS Fourteen nonfasted female Sprague-Dawley rats weighing from 300 to 400 gm were anesthetized with pentobarbital and placed on a warming blanket. A tracheostomy tube was inserted and the rats were permitted to breathe room air. Carotid arterial canhulas were inserted into the aortic arch to monitor systemic blood pressure and obtain samples of blood to measure pH and blood gas tensions. Hind limb adductor muscles were exposed through a small incision and modified Ling-Gerard microelectrodes were used to measure the resting Em as previously reported? '6 An open biopsy specimen of an adjacent muscle was taken by freeze-clamping and the tissue sample was analyzed for concentrations of ATP and creatine phosphate by enzymatic methods previously described, z'6 The abdominal aorta was exposed through a midline incision and after full heparinization it was occluded with a vascular clamp just below the renal arteries. After 60 minutes of aortic occlusion, Ems were measured and muscle samples were obtained for analysis. As the aortic clamp was removed, seven rats received by intra-aortic injection 6000 units of bovine liver SOD suspended in 2 ml of 5% dextrose in water, and seven control animals received 2 ml of a dilute heparin solution (100 units heparin/10 ml normal saline solution). After 30 minutes of reperfusion of the hind limbs, Em measurements and muscle biopsies were repeated on a contralateral hind limb adductor muscle. At the conclusion of the experiment the animals were killed by the administration of an overdose of barbiturate. The data were analyzed by standard statistical methods with analysis of variance and the NewmanKeuls test used for multiple comparisons of means.
Table II. Measurement of membrane electrical potentials and adenosine triphosphate levels in rats receiving superoxide dismutase (N = 7)
Control Ischemia Reperfusion (with SOD)
Em (mV)
A TP (la~llgm wet tissue)
94.4 + 0.7 76.6 _+ 2.8* 88.4 _+ 2.8t
7.3 + 0.1 6.0 _+ 0.7 7.1 -+ 0.2
*p < 0.05 vs. control. t p < 0.05 vs. ischemia.
The results are expressed as mean + the standard crror.
Animal care complied with the "Principles of Laboratory Animal Care" and the "Guide for the Care and Use of Laboratory Animals" (NIH Publication No. 80-23, revised 1978). RESULTS As can be seen in Table I, during the period of ischemia in the control rats there was marked deterioration of the Era, which failed to recover during reperfusion. Throughout the time of this experiment, intracellular levels of ATP remained within a normal range.
In Table II it is seen that the administration of SOD prevented the progressive deterioration of Ems during the reperfusion period. In contrast to the control studies, the Em returned to near normal levels immediately after reperfusion in those animals that received SOD just as the aortic clamp was removed. DISCUSSION The Em is generated by an ATP-dependent pump that moves sodium and potassium against their electrochemical gradients. The Em is determined by the magnitude of these gradients and the different permeabilities of the membrane to sodium and potassium. A decrease in the Em can result from a change in the gradients or a change in the ion permeability of the cell membrane. These studies clearly showed alterations in cell membrane function, changes that continued into the reperfusion period after partial ischemia, but not after total ischemia. The deterioration of the Em apparently is not related to sodium-potassium pump failure from lack of fuel because ATP levels remained adequate. Moreover, the membrane damage is not caused by excessive lactate since levels of this metab-
Volume 6 Number 3 September 1987
olite also immediately returned to normal with restoration of blood flow. s'6 Although the damage to the cell membrane could be the result of some other mechanism, the evidence strongly incriminates oxygen-derived free radicals. Other possibilities exist; for instance, studies of perfused cardiac muscle have demonstrated that when calcium is removed from the perfusate and then reintroduced, cellular damage results. This has been called the "calcium paradox. "~3 A similar situation may exist during partial skeletal muscle ischemia; the primary source of superoxide in reoxygenated cardiac muscle appears to be the enzyme xanthine oxidase, released during ischemia by a calcium-triggered proteolytic attack on xanthine dehydrogenase.14 The clinically observed resistance of skeletal muscle to ischemic injury, relative to other tissues, has been thought to occur because skeletal muscle xanthine dehydrogenase might not convert with nonperfusion. H However, many of these studies were performed in experiments with total ischemia; as the preceding data suggest, there apparently is more likelihood of dysfunction after partial ischemia than after total ischemia, at least within the time frame of 3 hours or less. is In some of the experimental models free radical scavengers have been shown to reduce or prevent cell injury, and recent reports suggest that with total ischemia muscle necrosis can be reduced by the administration of free radical scavengers. H,~4There is evidence that if arterial occlusion is complete, other mechanisms not dependent on free radical generation become the dominant factor, and then pretreatment with free radical scavengers fails to prevent ischemic damage. Moreover, at least in the intestine, the dominant mechanism of injury appears to change when partial ischemia is progressing to complete ischemia, but in cardiac muscle complete ischemia appears to be primarily a worse case of partial ischemia.7 Ninety-eight percent of molecular oxygen is completely reduced to water in the process of respiration; the other 2% can turn into potentially toxic free radicals. It appears that if anything less than complete full reduction of oxygen to water occurs, intermediate substances will be generated, and they must be dealt with in some way. 7'H The major source of superoxide in postischemic tissues appears to be the enzyme xanthine oxidase, which is widely distributed in the body. The enzyme is synthesized as xanthine dehydrogenase (type D); this accounts for about 90% of the total activity in healthy tissue. The conversion of xanthine dehydrogenase to xanthine oxidase (type O) begins when the
Ischemia: Reperfusion injury of skeletal muscle 233
decrease in blood flow to the tissue limits the availability of ATP. As the cell energy charge drops, it is no longer able to maintain a proper ion gradient across its membrane. This precipitates a redistribution of calcium and leads to increased amounts of adenosine monophosphate (AMP). The AMP is catabolized to adenosine, inosine, and hypoxanthine. Therefore, a new enzyme activity appears along with hypoxanthine, one of its two required substrates. 1~ The remaining substrate, molecular oxygen, needed for the generation of type O activity, is supplied during the reperfusion of the tissues, and with it comes a burst of superoxide radicals. Perhaps in the partial ischemia model this activity is present during the period of ischemia and then is accentuated further with reperfusion, as suggested by the progressive deterioration of the Em. Although other scavengers of oxygen-derived free radicals may be equally or more effective than SOD in protecting skeletal muscle from ischemic damage, SOD clearly offered some benefit in this clinically relevant model of temporary abdominal aortic occlusion. The toxic hydroxyl radical, known to cause lipid peroxidation of the cell membrane, is susceptible to neutralization by the administration of mannitol and other scavengers. In experimental models studying ischemic cardiac and skeletal muscle, pretreatment with mannitol has been shown to be of benefit; perhaps the mechanism of its action does not reside in its osmotic activity but rather in its ability to act as a scavenger of these toxic agents. ~6The selective administration of agents that block specific radicals may permit the identification of those scavengers that have clinical usefulness in preventing ischemic damage after temporary arterial occlusion. REFERENCES
1. Eldof B, Neglan P, Thompson D. Temporary incomplete ischemia of the legs induced by aortic clamping in man. Ann Surg 1980;93:89-98. 2. Perry MO, Shires GT III, Albert SA. Cellular changes with graded limb ischemia and reperfusion. J VASe StJrt¢; 1984; 1:536-40. 3. Bulldey GB. The role of oxygen free radicals in human disease processes. Surgery 1982;94:407-11. 4. Fischer EG, Ames A. Studies on mechanisms of impairment of cerebral circulation following ischemia: effect of hemodilution and perfusion pressure. Stroke 1972;3:538-46. 5. White BC, Wiegenstein JG, Winegar CD. Brain ischemic anoxia. Mechanisms of injury. JAMA 1984;251:1586-90. 6. Roberts JP, Perry MO, Hariri RJ, Shires GT. Incomplete recovery of muscle cell function following partial but not complete ischemia. Circ Shock 1985;17:253-8. 7. McCord JM. Oxygen-derived free radicals in postischemic tissue injury. N Engl J Med 1985;312:159-63. 8. Parks DA, Bulkley GB, Granger DN. Role of oxygen-derived
234
9.
10. 11. 12. 13.
Journal of VASCULAR SURGERY
Perryand Fantini
free radicals in digestive tract diseases. Surgery 1983;94: 415-21. 8anfey H, Bulkley GB, Cameron JL. The pathogenesis of acute pancreatitis. The source and role of oxygen-derived free radicals in three different experimental models. Ann Surg 1985;201:633-9. Parks DA, Bulkley GB, Granger DN. Role of oxygen free radicals in shock, ischemia, and organ preservation. Surgery 1983;94:428-32. McCord JM. Defense against free radicals has therapeutic implications. JAMA 1984;251:2187-92. Buchbinder D, Karmody AM, Leather RP, Shah DM. Hypertonic mannitol. Arch Surg 1981;8:8091-7. Zimmerman ANE, Daenes W, Halsman WC, Snyder ],
Wisse E, Durrer D. Morphological changes of heart muscle caused by successive perfusion of calcium-free or calciumcontaining solutions (calcium paradox). Cardiovasc Res 1967;1:201-9. 14. Gardner TJ, Stewart JR, Casale AS, Downey JM, Chambers DE. Reduction of myocardial ischemia injury with oxygenderived free radical scavengers. Surgery 1983;94:423-7. 15. Haljamae H, Enge E. Human skeletal muscle energy metabolism during and after complete tourniquet ischemia. Ann Surg 1975;183:9-16. 16. WiUerson JT, Powell WJ, Guiny TE. Improvement in myocardial function and coronary blood flow in ischemic myocardium after mannitol. J Clin Invest 1972;11:2981-94.
B O U N D VOLUMES AV.AH.ABLE TO SUBSCR/BERS Bound volumes of the JOURNAL OF VASCULAg SURGERY for 1987 are available to subscribers only. They may be purchased from the publisher at a cost of $44.00 ($58.00 international) for Vol. 5 (January to June) and Vol. 6 (July to December). Price includes shipping charges. Each bound volume contains a subject and author index, and all advertising is removed. Copies are shipped within 60 days after publication of the last issue in the volume. The binding is durable buckram with the journal name, volume number, and year stamped in gold on the spine. Payment must accompany all orders. Contact Circulation Fulfillment, The C. V. Mosby Company, 11830 Westline Industrial Drive, St. Louis, MO 63146, USA. In the United States call toll free: (800)325-4177, ext. 351. In Missouri call collect: (314)872-8370, ext. 351. Subscriptions must be in force to qualify. Bound volumes are not available in place of a regular JOURNAL subscription.