Maturational difference in functional/metabolic sequelae of free radical formation on reperfusion

To detect maturational differences with ischemia/reperfusion injury on cardiac metabolism and function, isolated nonworking rabbit hearts were subjected to 30 min of 37 degrees C ischemic arrest and reperfusion. Pre- and postischemic high energy phosphate contents (ATP, ADP, AMP), conjugated diene (products of free radical mediated lipid peroxidation) production, and peak isovolumic developed pressure (PDP) were measured in newborn (3-5 days, n = 8), 2- to 3-week-old (n = 8), and adult (2-4 months, n = 8) rabbits. ATP content decreased significantly during ischemia in all three age groups but recovered significantly toward preischemic levels in the newborn and 2-week-old groups but not in adult animals. AMP was much better preserved in the two younger groups with significantly higher levels at end-ischemia. Conjugated dienes were present in newborn and adult heart in small amounts at preischemia and rose slightly by end-ischemia. Newborn hearts accumulated large amounts of dienes by 10 min of reperfusion, which were significantly greater than those adult hearts. PDP returned to 85 and 91% of control in newborn and 2-week-old hearts, respectively, and to only 66% of control in adult hearts (P less than 0.05). These data suggest that the postischemic immature heart recovers energy stores and ventricular function faster than the adult heart which can be attributed to preservation of the total adenine nucleotide pool during ischemia. This improved recovery occurs despite a greater amount of free radical-mediated lipid peroxidation with reperfusion in newborn hearts.     

抑肽酶对成年豚鼠心肌再灌注损伤的保护作用

目的：探索抑肽酶的心肌保护作用。方法：建立离体心脏顺行灌注后左心做功模型，２０只成年豚鼠随机分为Ａ、Ｂ两组，分别以４℃Ｓｔ．ＴｈｏｍａｓＨｏｓｐｉｔａｌｃａｒｄｉｏｐｌｅｇｉｃｓｏｌｕｔｉｏｎＮｏ．２（ＳＴＳ）和ＳＴＳ＋抑肽酶（１５０ＫＩｕｍＬＳＴＳ）为心停搏液，测定缺血（９０分钟，２０℃）前、后和再灌注（６０分钟）时心脏动力学指标，心肌腺苷酸和丙二醛含量，并行心肌电镜观察。结果：Ｂ组再灌注后的心功能恢复，腺苷酸贮备和超微结构的改善明显高于或优于Ａ组，而丙二醛含量显著低于Ａ组（Ｐ＜０．０５）。结论：抑肽酶加入ＳＴＳ中可减少氧自由基产生，对成年豚鼠心肌缺血再灌注损伤有保护作用。     

Oxygen Free Radicals in Cardiac Transplantation

Abstract After prolonged ischemia, reperfusion of the myocardium with oxygenated blood results in high levels of superoxide anions. Several mechanisms for superoxide anion generation have been proposed, including increased xanthine oxidase activity, neutrophil activation, and arachidonate cascade activation. Superoxide anion accumulation may cause enzyme inactivation and lipid peroxidation in the sarcolemma with resultant intracellular calcium accumulation and excitation-contraction uncoupling. A review of a number of animal studies has shown that free radical scavengers such as superoxide dismutase and catalase can preserve myocardial function and metabolism during transplantation. In addition, other data indicate a role for inhibitors of free radical generation (i.e., allopurinol or oxypurinol), iron chelators (i.e., deferoxamine), or metabolic substrates such as L-glutamate in the inhibition of free radical myocardial injury. In addition, glutathione has been demonstrated to produce faster recovery of ventricular function in hypothermia preserved and reperfused rat hearts, presumably by inhibiting free radical production. Confirmatory data for human cardiac transplantation is not yet available.     

吡那地尔预处理对缺血心肌的保护效果

目的观察心肺转流(cardiopulmonory bypass,CPB)下,ATP敏感性钾通道开放剂(KCOs)吡那地尔(pinacidil)预处理分别对常温和低温高钾停跳心肌的保护作用.方法18只犬均分为三组,CPB心脏高钾停跳,全心缺血60 min,恢复灌注30 min.常温吡那地尔组(NP组)、低温吡那地尔组(HP组)CPB前主动脉根部灌注浓度为10 μmol/L的吡那地尔5 min.对比观察阻断主动脉前、后心肌超微结构、丙二醛(MDA)含量、血清心肌酶含量以及血液动力学的变化.结果(1)电镜:HP组除阻断60min外的其他时点心肌的正常线粒体及糖原含量均接近缺血前水平,明显高于C组和NP组;(2)心肌MDA的含量:HP组阻断30 min和开放20 min以及NP组开放20 min与C组有显著性差异;(3)血清心肌酶:HP组,除阻断30 min,CK-MB均明显低于同期C组;(4)血液动力学变化:HP组开放循环后心输出量(CO)、左室搏出功(LVSW)恢复比C组迅速.结论吡那地尔明显增强低温CPB心肌缺血-再灌注期超微结构的保护效果.     

Developmental changes in reperfusion injury. Comparison of intracellular ion accumulation in ischemic and cardioplegic arrest

Developmental differences in ischemic and potassium cardioplegic arrest were evaluated in newborn (birth to 7 day old) and adult (6 to 12 month old) New Zealand white rabbit hearts isolated and perfused by Langendorff's method. An extracellular space washout technique was used to measure intracellular sodium and calcium in the two age groups after ischemia alone, after normothermic and hypothermic cardioplegia, and after cardioplegia with reperfusion. Although the intracellular ionic contents of nonreperfused adult hearts after 30 and 40 minutes of ischemia were identical, there was a twofold elevation in intracellular sodium level after 40 minutes of ischemia in the newborn hearts. Adult hearts arrested by normothermic potassium cardioplegia demonstrated no alteration in the intracellular ionic content, whereas in the newborn hearts, potassium cardioplegia produced excess intracellular calcium loading before reperfusion, which was greater than that occurring with ischemia alone. When hypothermia (12 degrees C) was combined with cardioplegic arrest, a prereperfusion influx of sodium and calcium was not observed in the newborn hearts, and ionic reperfusion injury was blunted in both newborn and adult hearts. These studies demonstrate that the newborn heart is more susceptible than the adult to both ischemia and cardioplegia. This may be due to age-dependent differences in transmembrane passive diffusion, sodium/calcium exchange, or calcium slow channel properties and suggests alternative myocardial protective strategies for the newborn infant.     

Functional and metabolic protection of the neonatal myocardium from ischemia. Insufficient protection by cardioplegia

The effects of ischemia and cardiac arrest by cardioplegia on the mechanical function and energy metabolism of the ventricular myocardium of the neonatal guinea pig were investigated in the isolated perfused heart preparation and compared with these effects in the adult guinea pig. Whereas reperfusion after ischemia resulted in better recovery of mechanical function and a higher adenosine triphosphase content in the neonatal myocardium than in the adult, recovery from cardiac arrest induced by St. Thomas' Hospital cardioplegic solution was not as good in the neonatal myocardium as in the adult. Contracture developed in the neonatal myocardium on administration of the cardioplegic solution, but did not in the adult. This was considered to be the reason that the protective effect of the cardioplegic solution was inferior in the neonatal myocardium to that in the adult.     

A promising approach for improving the recovery of heart transplants. Prevention of free radical injury through iron chelation by deferoxamine

Iron catalysis is involved in the generation of the highly cytotoxic hydroxyl radical and in the chain reactions of subsequent lipid peroxidation that lead to irreversible membrane damage. Assuming that ischemically stored heart transplants may incur free radical injury at the time of reoxygenation, we assessed the effects of the iron chelator deferoxamine in 70 isolated isovolumic buffer-perfused rat hearts subjected to the following protocol: cardioplegic arrest; cold (2 degrees C) storage for 5 hours; global ischemia at 15 degrees C for 1 hour, intended to simulate the implantation procedure; and normothermic reperfusion for 1 additional hour. During poststorage ischemic arrest, the following techniques of myocardial protection were evaluated: hypothermia alone; high-pressure (60 cm H2O) cardioplegia given at 0, 30, and 55 minutes of arrest; low-pressure (30 cm H2O) cardioplegia given at 0 and 55 minutes of arrest; and low-pressure (30 cm H2O) cardioplegia only given at 55 minutes of arrest. Treated hearts had deferoxamine (6 mumol) added to the cardioplegic solution used throughout the experimental time course. Further, in the treated group subjected to the protocol of single cardioplegic delivery at end ischemia, deferoxamine was given both in the cardioplegic reperfusate and in the Krebs buffer over the 15 initial minutes of reflow. Based on comparisons of postreperfusion ventricular pressure development, maximal rate of rise of ventricular pressure, left ventricular compliance, and coronary flow, the best myocardial protection was afforded by deferoxamine given as an additive to single-dose cardioplegic solution at the end of arrest and to the reperfusate during the initial phase of reoxygenation. As the drug has no inotropic effect, its protective action is most likely related to a decrease in catalytic iron available for free radical production and lipid peroxidation. These results support the hypothesis that oxidative damage may contribute to donor heart failure and demonstrate that this form of damage can be efficiently acted upon by iron chelation. The clinical relevance of these data stems from the fact that deferoxamine is available for human use and might become an effective means of improving donor heart preservation in the setting of clinical heart transplantation.     

The role of oxygen-derived free radicals and the effect of free radical scavengers on skeletal muscle ischemia/reperfusion injury

The aim of this study was to clarify the role of oxygen-derived free radicals and the effect of free radical scavengers on skeletal muscle ischemia/reperfusion injury. Male Wistar rats were divided into a complete ischemia group (C-group) and an incomplete ischemia group (IC-group) and each animal was subjected to 2h of ischemia and 1h of reperfusion. In an attempt to decrease reperfusion injury, the rats were given free radical scavengers either as allopurinol 50 mg/kg for 2 days or as superoxide dismutase 60,000 units/kg plus catalase 500,000 units/kg. Tissue malondialdehyde, a product of lipid peroxidation, was measured as an indicator of free radicals, with higher levels indicating higher concentrations of free radicals. The malondialdehyde level in the gastrocnemius muscle after 1h of reperfusion increased significantly in both groups when compared to the levels before and 2h after ischemia, although there was no significant difference between the two groups. The water content of the gastrocnemius muscle and serum creatinine phosphokinase MM isoenzyme (CPK-MM) in both groups, and GOT in the C-group, increased significantly after 1h of reperfusion when compared the values before and 2h after ischemia. In the C-group, these values were significantly higher than in the IC-group. The administration of free radical scavengers suppressed the increase in malondialdehyde in the gastrocnemius muscle after reperfusion in both groups. The increase in water content and CPK-MM after reperfusion was also suppressed by free radical scavengers in the IC-group, but not in the C-group. These findings suggest that ischemic damage predominates in complete severe ischemia/reperfusion injury, whereas reperfusion injury predominates in incomplete mild ischemia/reperfusion injury.     

左旋精氨酸与氧自由基的相互作用

目的：研究左旋精氨酸与氧自由基间的相互作用。方法：１４只离体大白鼠心脏模型,分别予含５％左旋精氨酸高钾停跳液（实验组）或单纯高钾停跳液（对照组）,使心脏停博６０分钟,再以ＫＨＢＢ缓冲液复灌３０分钟。观察复灌后鼠心的冠脉流量、心搏率和左室内压,并测定心肌匀浆内乳酸（ＬＡ）、丙二醛（ＭＤＡ）、黄嘌呤氧化酶（ＸＯＤ）和超氧化物歧化酶（ＳＯＤ）含量。结果：复灌时实验组冠脉流量明显多于对照组,鼠心搏率和节律     

Protection of the pediatric myocardium. Differential susceptibility to ischemic injury of the neonatal rat heart

Myocardial protection during pediatric cardiac operations has been suggested to be less successful than in adult hearts. In the present study we have compared the resistance of adult, infant, and neonatal rat hearts to various periods of ischemic arrest with normothermic (37 degrees C) crystalloid cardioplegia. Isolated hearts with intraventricular balloons, from adult (50 to 60 days of age, heart weight 865 +/- 13 mg), infant (20 to 25 days of age, heart weight 251 +/- 3 mg), and neonatal rats (3 to 5 days of age, heart weight 40 +/- 1 mg) were subjected to 10, 20, 30, 40, 50, 60, 80, and 100 minutes of ischemia (n = 6 hearts for each time point and for each age group). St. Thomas' Hospital cardioplegic solution was infused at the onset of the period of arrest. With increasing durations of ischemia there was a declining postischemic recovery of function. Up to 40 minutes of ischemia there was no significant difference between the three age groups in postischemic recovery of left ventricular developed pressure: 40.3% +/- 4.4%, 45.4% +/- 6.5%, and 44.4% +/- 2.2% of preischemic control for adult, infant, and neonatal hearts, respectively. Beyond 40 minutes adult and infant hearts showed an identical deterioration with effectively no recovery beyond 60 minutes of ischemia. By contrast, neonatal hearts were much more resistant to ischemia. After 100 minutes of ischemia the mean recovery of left ventricular developed pressure was 20.9% +/- 1.1%, whereas in infant and adult hearts the values were 0.6% +/- 0.3% after 80 minutes of ischemia and 0% after 100 minutes, respectively. Analysis of creatine kinase leakage also indicated that with ischemic durations in excess of 40 minutes, the neonatal heart was far more resistant to ischemia, and creatine kinase leakage per gram dry weight was much less than in infant or adult rats. Analysis of the rates of recovery during reperfusion again revealed differences between neonatal hearts and hearts from the other two age groups. We conclude that in the normal rat the neonatal heart has a greater inherent tolerance to ischemia than that of the infant or adult rat.     

Intracoronary platelet aggregation: pattern of deposition after ischemia, cardioplegia, and reperfusion

Platelet deposition in the coronary microvasculature has not been completely defined in the temporal relationship to acute myocardial ischemia, the application of crystalloid cardioplegia, and during reperfusion on heart bypass. Twenty-two canine hearts were serially biopsied for the analysis of radioactively tagged platelets. Eleven hearts underwent an isolated heart support preparation with seven followed by potassium cardioplegic arrest and reperfusion while the remaining 4 were maintained on continuous bypass. All 11 hearts undergoing bypass experienced transient (less than 90 sec) ischemia during bypass preparation and produced platelet aggregation in the myocardium (51.12 +/- 24.0 as compared to nonischemic control group 12.3 +/- 4.7; P = 0.005). Potassium cardioplegia did not completely wash out these platelets to the nonischemic control levels (27.8 +/- 14.9; P = 0.04). With the onset of reperfusion after 1 hr of cardioplegic arrest, platelet radioactivity profoundly increased (133.3 +/- 72.8; P = 0.0101) and remained high throughout the hour of reperfusion (324.7 +/- 269.3; P = 0.0369). In summary, intracoronary platelets are activated after transient ischemic episodes during initiation of heart bypass. These ischemia-activated platelet aggregations persist despite the application of cardioplegia during the arrest period. This deposition, in turn, allowed an ongoing pattern of platelet aggregation during the early and subsequent reperfusion. This pattern of ischemia-activated platelet aggregations probably accounts for the progressive reperfusion injury and support of an antiplatelet treatment for coronary microvasculature protection.     

Coronary blood flow and myocardial metabolism during reperfusion after hypothermic cardioplegia in the dog

There have been many studies of reperfusion injury after normothermic ischemia. However, there have been few clinically relevant studies on the nature and time course of recovery of the myocardium during reperfusion after hypothermic cardioplegia. We studied reperfusion in the isolated dog heart supported by another dog. After 2 h of cardioplegic arrest at 20 degrees C, 11 normal hearts were reperfused for 30 min at optimal coronary pressures (60-100 mm Hg mean). The following events occurred: rapid rewarming, a transient hyperemia followed by a rapid return of both coronary blood flow and myocardial oxygen consumption to normal, washout of lactate, recovery of contractility and a slight decline in ATP. Most of these events occurred during the first 15 min of reperfusion. We concluded that, in normal hearts which are well protected during hypothermic cardioplegia, reperfusion at optimal coronary pressure results in recovery of the myocardium within 15 min, with the exception of recovery of ATP levels.     

Protection of the neonatal heart following normothermic ischemia: a comparison of oxygenated saline and oxygenated versus nonoxygenated cardioplegia

Optimal methods of myocardial preservation in the neonate remain unknown. Hypothermia and cardioplegia have been shown to protect neonatal hearts, but few studies have examined the effects of cardioplegia when administered at normothermia. Accordingly, the role of 37 degrees C St. Thomas' cardioplegic solution in protecting the neonatal heart during 1 hour of ischemia in an isolated working rabbit heart model was examined. Both oxygenated and nonoxygenated cardioplegic solutions (CSs) were evaluated and compared with an oxygenated physiological saline solution (PSS). Following ischemia, control hearts were characterized by severely impaired left ventricular function, whereas all three treatment groups recovered well, indicating that the treatments provided substantial protection. Aortic flow recovered to 62, 63, and 57% of preischemic values for the oxygenated CS, nonoxygenated CS, and oxygenated PSS groups, respectively. Similarly, rate of change of pressure recovered to 76, 80, and 76% of preischemic values for oxygenated CS, nonoxygenated CS, and oxygenated PSS groups. All values were significantly greater than those for the control group. Recovery of developed pressure was significantly improved in all three groups. End-diastolic pressure rose markedly following ischemia in control hearts, was not increased after ischemia in hearts receiving oxygenated and nonoxygenated CS, but was increased in the oxygenated PSS group. These data indicate that crystalloid cardioplegia and oxygenated PSS provide substantial protection in neonatal rabbit hearts, even when delivered at 37 degrees C. No additional benefit was seen when the cardioplegic solution was oxygenated. Therefore, either method of balancing the oxygen supply/demand ratio appears to be beneficial: supplying oxygen intermittently during ischemia (oxygenated PSS group) or decreasing oxygen demand during the ischemic period (cardioplegia groups).     

Oxygen-derived free radical damage in canine heart transplantation

To study the role of free radical-induced myocardial injury during heart transplantation, five groups of dog hearts were orthotopically transplanted. Control group I and experimental groups II, III, and IV (each n = 8) were reperfused for 1 hr after 49 min of operational ischemia. Control group V (n = 4) remained ischemic for 90 min. In the three experimental groups, the free radical scavengers superoxide dismutase (10 mg/kg; group II), catalase (10 mg/kg; group III), or both (10 mg/kg each; group IV) were administered just before reperfusion and during reperfusion for 1 hr. The generation of free radicals, remained at low levels in all groups during ischemia, but significantly increased when groups I-IV were reperfused. This increase was also associated with an increase in creatinine kinase MB isoenzyme. In the experimental groups, free radical scavengers significantly inhibited the appearance of thiobarbituric acid reactive substances and the release of creatinine kinase MB isoenzyme during reperfusion (P less than 0.05). Regarding cardiac functions, 60 min after the termination of the cardiopulmonary bypass, a significant improvement was demonstrated in the treated groups (P less than 0.05). These results indicate that (1) the generation of oxygen free radicals occurs primarily during reperfusion, (2) both superoxide dismutase and catalase reduce production of free radicals during this time, and (3) combined administration did not provide a greater improvement in cardiac metabolic recovery. This study confirms the efficacy of free radical scavengers during heart transplantation.     

Oxygenated perfluorocarbon, recombinant human superoxide dismutase, and catalase ameliorate free radical induced myocardial injury during heart preservation and transplantation

The effect of free radical scavengers on free radical-induced myocardial injury during heart preservation and transplantation was examined. Four groups of nine hearts each were harvested from mongrel dogs (12.5 to 16.5 kg) and orthotopically transplanted to size-matched recipients. All hearts received a continuous perfusion of oxygenated modified Collins' solution (group A). In addition, groups B, C, and D received Fluosol DA and albumin. Preservation perfusion was performed for 18 hours, at 4 degrees C, pH = 7.4, and 20 mm Hg. In group C, recombinant human superoxide dismutase (4,080 U/mg, 20 mg/kg) and bovine catalase (46,200 U/mg, 20 mg/kg) were administered only during preservation perfusion. In group D, these scavengers were administered just before and during reperfusion for 1 hour. Hemodynamic studies were performed before excision of the donor hearts and 1 hour after the termination of cardiopulmonary bypass. Creatinine kinase MB isoenzyme and thiobarbituric acid reactive substance levels in the coronary effluent were determined during preservation perfusion and reperfusion. Only group A showed a significant heart weight gain (p less than 0.05) and a decline in passive compliance (p less than 0.05) during preservation. Lactate release was higher in group A than in the groups receiving Fluosol DA. In contrast, pyruvate levels in group A were lower than in other groups. The generation of free radicals stayed at a low level during preservation, but significantly increased during reperfusion and was associated with a corresponding increase in creatinine kinase MB isoenzyme. Perfusion with a perfluorochemical solution (group B) inhibited the sharp rise in levels of thiobarbituric acid reactive substances and of creatinine kinase MB isoenzyme and improved cardiac function during reperfusion (versus group A). Exogeneous free radical scavengers administered just before and during reperfusion (group D) significantly ameliorated thiobarbituric acid reactive substances and creatinine kinase MB isoenzyme levels and also induced a significant hemodynamic improvement during reperfusion. However, administration of scavengers during preservation did not. This study demonstrates that the generation of free radicals is primarily significant during reperfusion and reoxygenation after ischemia. Thus the best time for administration of scavengers is just before and just after the onset of reperfusion. Furthermore, perfusion with perfluorochemicals effectively maintains aerobic metabolism and ameliorates free radical damage during this period.     

Myocardial protection of neonatal heart by cardioplegic solution with recombinant human superoxide dismutase.

The effectiveness of high-potassium cardioplegic solution in the neonatal heart remains controversial. Our previous study indicated that the protection afforded by a cardioplegic solution was inadequate in the neonatal heart. On the hypothesis that oxyradicals were responsible for the ineffectiveness of cardioplegic solution in neonatal heart, the effects of a cardioplegic solution (a modified St. Thomas' Hospital cardioplegic solution) with recombinant human superoxide dismutase on the isolated perfused neonatal guinea pig hearts (within 2 days after delivery, body weight of 60 to 120 g) were studied in comparison with those on the adult hearts (6 to 8 weeks after delivery, body weight of 300 to 500 g). After arrest induced by modified St. Thomas' Hospital cardioplegic solution, hearts were subjected to 120 min of ischemia at 20 degrees C, during which time the cardioplegic solution was injected every 30 minutes. Then the heart was reperfused for 60 minutes at 37 degrees C. Under this condition, the left ventricular developed pressure recovered to 84.4% +/- 4.0% of the preischemic value in the adult heart, whereas the recovery was only 68.1% +/- 3.1% in the neonatal heart. Thiobarbituric acid-reactive substance level, a parameter of lipid peroxidation by oxyradicals, significantly increased during ischemic arrest both in the adult and neonatal heart. However, the increase was much greater in the neonatal heart than in the adult. Cardioplegia with recombinant human superoxide dismutase (300 and 1,000 U/mL) significantly inhibited this accumulation of thiobarbituric acid-reactive substance in the neonatal heart; at 1,000 U/mL, the myocardial function of the reperfused neonatal heart recovered to the level of the adult heart.(ABSTRACT TRUNCATED AT 250 WORDS)     

缺血-再灌注不同时期应用1,6-二磷酸果糖对幼兔心脏的保护作用

目的　研究在缺血 再灌注的不同时期 1,6 二磷酸果糖 (FDP)对幼兔离体心脏的保护作用。方法　建立幼兔离体心脏做功模型 ,行缺血 再灌注试验 ,于缺血 再灌注的不同时期给予5mMFDP ,观察再灌注期的心功能、心肌组织含水量、心肌MDA、冠脉液CK含量以及心肌超微结构的变化。结果　缺血期给药组与缺血前给药组和再灌注期给药组比较 ,缺血期给药组的心功能恢复百分率、心肌超微结构优于后两组 ,缺血期给药组的冠脉液CK含量、心肌组织含水量和MDA含量显著低于后两组。结论　缺血期给 1,6 二磷酸果糖对幼兔心肌缺血 再灌注损伤的保护优于缺血前或者再灌注期给药     

ATP precursor depletion and postischemic myocardial recovery

Although cardioplegia reduces myocardial metabolism during ischemia, adenosine triphosphate (ATP) depletion occurs, which may contribute to poor functional recovery after reperfusion. Augmenting myocardial adenosine during ischemia is successful in improving ATP repletion and myocardial recovery following ischemia. If adenosine is an important determinant of ischemic tolerance, then depletion or elimination of myocardial adenosine should lead to poor functional and metabolic recovery after ischemia. To test this hypothesis, isolated, perfused rabbit hearts were subjected to 120 min of 34 degrees C ischemia. Hearts received St. Thomas cardioplegia alone or cardioplegia containing 200 microM adenosine, or cardioplegia containing 15, 5, 2.5, or 0.025 micrograms/ml adenosine deaminase (ADA), which catalyzes the breakdown of adenosine to inosine, making adenosine unavailable as an ATP precursor. Functional recovery was determined and myocardial nucleotide levels were measured before, during, and after ischemia. Following ischemia and reperfusion, control hearts recovered to 51 +/- 3% of preischemic developed pressure (DP). There was significantly better recovery in adenosine-augmented hearts (68 +/- 7%), while ADA hearts had significantly worse recovery. Hearts treated with 0.025 microgram/ml ADA recovered to only 29 +/- 5% of DP and higher dose ADA hearts failed to demonstrate any recovery of systolic function. Furthermore, adenosine enhanced metabolic recovery, whereas ADA resulted in greatly depleted ATP and precursor reserves. Postischemic developed pressure closely paralleled the availability of myocardial adenosine, consistent with the hypothesis that myocardial adenosine levels at end ischemia and early reperfusion are important determinants of functional recovery after global ischemia.     

Terminal magnesium cardioplegia: protective effect in the isolated rat heart model using calcium accentuated ischemic damage

We have developed a modified isolated working rat heart model to study the effect of potassium and magnesium cardioplegia given just prior to reperfusion, "terminal cardioplegia," on preservation of aortic flow following a standard ischemic insult. The model incorporates a short-term calcium challenge at the beginning of reperfusion to accentuate ischemic injury. All hearts were given initial potassium cardioplegia and subjected to 30 min of normothermic ischemia. Terminal cardioplegia was given for the 2 min prior to reperfusion. Calcium-challenged hearts were reperfused initially with calcium-enriched reperfusate and then switched to standard reperfusate. Aortic flow prior to and 60 min after ischemia was used to determine functional protection. Hearts recovered 82 +/- 3% of preischemic aortic flow when reperfused with normocalcemic reperfusate. When the initial reperfusate was enriched with calcium, aortic flow was only 43 +/- 4% of control. Hearts given terminal magnesium cardioplegia and then challenged with calcium-enriched reperfusate recovered 79 +/- 4% of control aortic flow. Hearts given terminal potassium cardioplegia recovered only 53 +/- 5% of control aortic flow when challenged with calcium-enriched initial reperfusate. Our results indicate that the recovery of aortic flow is significantly reduced by short-term postischemic calcium challenge. This damage is blocked by terminal magnesium cardioplegia, but not by terminal potassium cardioplegia.     

The role of reperfusion injury in occlusive intestinal ischemia of the neonate: malonaldehyde-derived fluorescent products and correlation of histology

Oxygen free radical reperfusion products may play a critical role in neonatal occlusive intestinal ischemia. We report a comparative analysis of light microscopy- and malonaldehyde (MDA)-derived fluorescent products as a measure of lipid peroxidation in occlusive intestinal ischemia in the rat. Weanling rats (n = 25) underwent cross clamping of the common mesenteric artery followed by various intervals of reperfusion; blood was sampled from the common mesenteric vein and the ileum was simultaneously biopsied. Blind-light microscopic scoring of the ischemic intestine was used. Fluorescent products were extracted using a chloroform/methanol/acidic water solvent extraction and measured with a spectrophotofluorometer using excitation/emission wavelengths of 360 and 430 nm, respectively. A trend was observed with prolonged reperfusion. Accumulation of fluorescent products correlated directly with the interval of reperfusion. Graded intervals of vascular occlusion produced progressive intestinal injury, but light microscopic analysis was not a sensitive index to distinguish the influence of graded reperfusion intervals. These data confirm a role for both ischemia and reperfusion in occlusive intestinal injury in the neonate and suggest that MDA accumulation may be a sensitive index of the reperfusion component of such injury.