Effect of ATP-potassium channel opener nicorandil on long-term cardiac preservation

BACKGROUND: ATP-sensitive potassium channels have been shown to be one of the important protective mechanisms for the ischemic myocardium. The purpose of this study was to evaluate the protective effect of nicorandil, an ATP-sensitive potassium channel opener, on myocardium during 6 hours hypothermic preservation. METHODS: Preserved rat hearts were randomly divided into 4 groups according to cardioplegia and preservation protocols as follows: (1) histidine-tryptophan-ketoglutarate solution (HTK) for both cardioplegic and immersing solutions (group A); (2) nicorandil-added HTK for cardioplegic solution and nicorandil-free HTK for immersing solution (group B); (3) nicorandil-free HTK for cardioplegic solution and nicorandil-added HTK for immersing solution (group C); and (4) nicorandil-added HTK for both cardioplegic and immersing solutions (group D). RESULTS: The recovery of postischemic cardiac function, including left ventricular developed pressure and end-diastolic pressure, was significantly improved in group B and group C as compared with the other groups (p<0.05). Postischemic intracellular calcium concentration was significantly lower in group B and group C than in group A (p<0.05). CONCLUSIONS: We concluded that nicorandil-induced hyperpolarizing arrest could reduce ischemia-derived myocyte injury and inhibit the influx of calcium into the myocytes in long-term cardiac preservation.     

Protectant activity of defibrotide in cardioplegia followed by ischemia/reperfusion injury in the isolated rat heart

BACKGROUND: Previous studies have shown that defibrotide, a polydeoxyribonucleotide obtained by depolymerization of DNA from porcine tissues, has important protective effects on myocardial ischemia, which may be associated with a prostacyclin-related mechanism. The purpose of this study was to investigate the direct effects of defibrotide (given in cardioplegia or after ischemia) on a model of rat heart recovery after cardioplegia followed by ischemia/reperfusion injury. METHODS: Isolated rat hearts, undergoing 5 minutes of warm cardioplegic arrest followed by 20 minutes of global ischemia and 30 minutes of reperfusion, were studied using the modified Langendorff model. The cardioplegia consisted of St. Thomas' Hospital solution augmented with defibrotide (50, 100, and 200 microg/mL) or without defibrotide (controls). Left ventricular mechanical function and the levels of creatine kinase, lactate dehydrogenase, and 6-keto-prostaglandin F1alpha (6-keto-PGF1alpha; the stable metabolite of prostacyclin) were measured during preischemic and reperfusion periods. RESULTS: After global ischemia, hearts receiving defibrotide in the cardioplegic solution (n = 8) manifested in a concentration-dependent fashion lower left ventricular end-diastolic pressure (p < 0.001), higher left ventricular developed pressure (p < 0.01), and lower coronary perfusion pressure (p < 0.001) compared to the control group. After reperfusion, hearts receiving defibrotide in the cardioplegic solution also had, in a dose-dependent way, lower levels of creatine-kinase (p < 0.01), lactate dehydrogenase (p < 0.001), and higher levels of 6-keto-PGF1alpha (p < 0.001) compared to the control group. Furthermore, when defibrotide was given alone to the hearts at the beginning of reperfusion (n = 7), the recovery of postischemic left ventricular function was inferior (p < 0.05) to that obtained when defibrotide was given in cardioplegia. CONCLUSIONS: Defibrotide confers to conventional crystalloid cardioplegia a potent concentration-dependent protective effect on the recovery of isolated rat heart undergoing ischemia/reperfusion injury. The low cost and the absence of contraindications (cardiac toxicity and hemodynamic effects) make defibrotide a promising augmentation to cardioplegia.     

Opioids confer myocardial tolerance to ischemia: interaction of delta opioid agonists and antagonists

BACKGROUND: Mammalian hibernation biology is now known to be mediated by delta opioids. The altered myocellular physiology of hibernation closely parallels that of hypothermic ischemia used to protect the heart for cardiac surgery. METHODS AND RESULTS: The present study examined the interaction of delta opioid agonists and antagonists on myocardial tolerance to ischemia. By means of a nonhibernating isolated rabbit heart model, functional and metabolic myocardial parameters were assessed during nonischemic baseline and postischemic recovery periods. Control hearts with standard cardioplegic protection alone were compared with those with cardioplegia plus preperfusion with a delta opioid agonist, a delta opioid antagonist, or both. All hearts were then subjected to 2 hours of global ischemia. Compared with cardioplegia alone, postischemic left ventricular developed pressure, coronary flows, and myocardial oxygen consumption were all increased with administration of delta opioid agonists and decreased below baseline with delta opioid antagonists. Functional recovery of left ventricular developed pressure was improved with opioids (control hearts: 36 +/- 3 mm Hg vs hearts with cardioplegia plus delta opioid agonist: 65 +/- 5 mm Hg, P <.01) and inhibited with antagonists (control hearts: 36 +/- 3 mm Hg vs hearts with cardioplegia plus delta opioid antagonist: 17 +/- 5 mm Hg, P <.05), and true to form, the protective opioid effect was negated when combined with an antagonist (control hearts: 36 +/- 3 mm Hg vs hearts with cardioplegia plus delta opioid agonist and delta opioid antagonist: 42 +/- 4 mm Hg, P = not significant). CONCLUSIONS: This study demonstrates that cardiac tolerance to ischemia may be mediated by delta opioids.     

Intracellular calcium increasing at the beginning of reperfusion assists the early recovery of myocardial contractility after diltiazem cardioplegia

Objectives: We investigated the ability of diltiazem to prevent myocardial injury by assessing heart function and intracellular calcium concentrations before and after ischemia-reperfusion. Method: Isolated rat hearts underwent cardioplegia using the Langendorff perfusion model and were subjected to normothermic global ischemia for 60 minutes. The recovery rates for the heart function (heart rate, coronary flow, left ventricular systolic pressure) after reperfusion were monitored, and the intracellular Ca concentration was measured during ischemia and during the following reperfusion. Experimental groups were divided into three groups according to the diltiazem concentration used in the cardioplegic solution (potassium 20 mmol/l in Ringer's solution): (1) Group A: diltiazem 2.5 mg/l; (2) Group B: diltiazem 5 mg/l; and (3) Group C: no diltiazem. Results: Intracellular calcium concentration increased in all 3 groups during ischemia, but was significantly lower in Group B compared to either Group A or Group C. The heart function was significantly higher for Group A than for Group B or Group C. The hearts in Group B displayed markedly poor recovery in contractility and in heart rate. Conclusions: Generally, a decrease in intracellular Ca concentration improves the heart function during ischemia and after reperfusion. However, this study showed that some increase in intracellular Ca at the beginning of reperfusion assisted the contractility of rat heart.     

Calcium content of St. Thomas' II cardioplegic solution damages ischemic immature myocardium

Clinical application of hypothermic pharmacologic cardioplegia in pediatric cardiac surgery is less than satisfactory, despite its well known benefits in adults. Protection of the ischemic immature rabbit heart with hypothermia alone is better than with hypothermic St. Thomas' II cardioplegic solution. Control of cellular calcium is a critical component of cardioplegic protection. We determined whether the existing calcium content of St. Thomas' II solution (1.2 mmol/L) is responsible for suboptimal protection of the ischemic immature rabbit heart. Modified hypothermic St. Thomas' II solutions (calcium content, 0 to 2.4 mmol/L) were compared with hypothermic Krebs bicarbonate buffer in protecting ischemic immature (7- to 10-day-old) hearts. Hearts (n = 6 per group) underwent aerobic "working" perfusion with Krebs buffer, and cardiac function was measured. The hearts were then arrested with a 3-minute infusion of either cold (14 degrees C) Krebs buffer (1.8 mmol calcium/L) as hypothermia alone or cold St. Thomas' II solution before 6 hours of hypothermic (14 degrees C) global ischemia. Hearts were reperfused, and postischemic enzyme leakage and recovery of function were measured. A bell-shaped dose-response profile for calcium was observed for recovery of aortic flow but not for creatine kinase leakage, with improved protection at lower calcium concentrations. Optimal myocardial protection occurred at a calcium content of 0.3 mmol/L, which was better than with hypothermia alone and standard St. Thomas' II solution. We conclude that the existing calcium content of St. Thomas' II solution is responsible, in part, for its damaging effect on the ischemic immature rabbit heart.     

Pretreatment with nicardipine preserves ventricular function after hypothermic ischemic arrest

Calcium antagonists have a protective effect on postischemic myocardial function when included in normothermic cardioplegia solutions. This effect varies with the calcium antagonist, but is generally lost under hypothermic conditions. The hypothesis tested was that a calcium antagonist would increase postischemic myocardial performance if given before the onset of hypothermic arrest. Isolated working rat hearts were used with an oxygenated modified Krebs-Henseleit buffer solution as a perfusion media. Rats were pretreated with 1 of 9 doses of a nicardipine solution (0 to 100 micrograms/kg, intraperitoneally) 20 minutes before excision of the heart. Nicardipine is a light-stable, water-soluble calcium antagonist with minimal myocardial depressant effects. The hearts were arrested for 25 minutes at 37 degrees C or 93 minutes at 24 degrees C with 20 mL of cardioplegia solution containing 0.05 mmol/L CaCl2. Postischemic performance and adenosine triphosphate content were used as determinants of efficacy. Eighty-three percent of 101 treated hearts recovered in contrast to a mortality of 50% in the 24 nontreated hearts. Pretreatment with 25 micrograms/kg significantly increased (p less than 0.05) the percent recovery (compared with the nontreated group) of the following variables of cardiac function: systolic pressure, 74% to 96% (37 degrees C), 76% to 90% (24 degrees C); cardiac output, 61% to 90% (37 degrees C), 62% to 84% (24 degrees C); stroke work, 49% to 95% (37 degrees C), 50% to 92% (24 degrees C); and adenosine triphosphate, 76% to 87% (37 degrees C), 58% to 68% (24 degrees C). Progressive increases in postischemic function at 37 degrees and 24 degrees C were seen as the dose of nicardipine was increased from 0 to 25 micrograms/kg and decreased function was seen with a pretreatment dose greater than 25 micrograms/kg of nicardipine. Pretreatment with nicardipine significantly improved postischemic myocardial performance under hypothermic conditions and should be administered or at least not discontinued before cardiac operations.     

含吡那地尔的心脏保存液对大鼠离体心脏线粒体呼吸功能的影响

目的 探讨含吡那地尔的心脏保存液(HTK液)对大鼠离体心脏线粒体呼吸功能的影响.方法 健康清洁级SD大鼠120只,建立离体心脏Langendorff灌注模型,随机分为5组,HTK组(Ⅰ组)、吡那地尔+HTK液组(Ⅱ组)、吡那地尔+HTK液+5-羟葵酸(5-HD)组(Ⅲ组)、吡那地尔+HTK液+HMR-1098组(Ⅳ组)、吡那地尔+HTK液+HMR-1098+5-HD组(Ⅴ组).K-H液平衡灌注10 min后灌注心脏停搏液:Ⅰ组灌注HTK液;Ⅱ组灌注含吡那地尔0.5 mmol/L的HTK液;Ⅲ组灌注含吡那地尔0.5 mmol/L和5-HD 100μmol/L的HTK液;Ⅳ组灌注含吡那地尔0.5 mmol/L和HMR-1098 100μmol/L的HTK液;Ⅴ组灌注含吡那地尔0.5 mmol/L、5-HD 100μmol/L和HMR-1098 100 μmol/L的HTK液.停搏后取心脏保存于4℃各组相应液体中8 h,然后用37 ℃含氧K-H液再灌注60 min.于平衡灌注10 min(T1)、保存8 h(T2)、复灌60 min(T3)时测定线粒体呼吸功能[3态呼吸(S3)和4态呼吸(S4)的耗氧速率、呼吸控制率(RCR)及磷氧比(P/O)].于T1和T3时收集冠脉流出液测定心肌肌钙蛋白I(cTnI)浓度、肌酸激酶同功酶(CK-MB)及乳酸脱氢酶(LDH)的活性.电镜下观察心肌细胞超微结构.结果 与Ⅰ组比较,Ⅱ组～Ⅳ组RCR、P/O、S3耗氧速率升高,cTnI、CK-MB和LDH的水平降低(P＜0.05).与Ⅱ组比较,Ⅲ组～Ⅴ组RCR、P/O、S3耗氧速率降低,cTnI、CK-MB和LDH的水平升高(P＜0.05).与Ⅲ组比较,Ⅳ组RCR、P/O、S3耗氧速率升高,cTnI、CK-MB和LDH的水平降低,Ⅴ组RCR、P/O、S3耗氧速率降低,cTnI、CK-MB和LDH的水平升高(P＜0.05).与Ⅳ组比较,V组RCR、P/O、S3耗氧速率降低,cTnI、CK-MB和LDH水平升高(P＜0.05).各时点S4耗氧速率组间比较差异无统计学意义(P＞0.05).Ⅱ组心肌细胞损伤较轻,Ⅲ组和Ⅳ组损伤程度相近但重于Ⅱ组,Ⅰ组和Ⅴ组损伤最重.结论 含吡那地尔的HTK液可改善心脏线粒体呼吸功能,减轻心肌损伤,提高心脏保存效果,线粒体ATP敏感性钾通道和细胞膜ATP敏感性钾通道均参与了吡那地尔的心肌保护效应,且线粒体ATP敏感性钾通道发挥主导作用.     

Arresting donor hearts with extracellular-type cardioplegia prevents vasoconstriction induced by UW solution.

The effects of arresting donor hearts with University of Wisconsin solution was investigated. Donor dogs were divided into two groups according to the technique used for arresting the heart. In group I (n = 6) the heart was arrested with University of Wisconsin solution, whereas in group II (n = 6) extracellular-type cardioplegia (K+ = 20 mmol/liter) was used to induce cardioplegic arrest. Aortic root pressure was measured during the infusion of solution at constant flow. In both groups, the hearts were then flushed and stored in cold University of Wisconsin solution for 6 h. The hearts were transplanted orthotopically and disconnected from cardiopulmonary bypass. Left ventricular function was evaluated by pressure-volume relations using a conductance catheter. Peak aortic root pressure during the infusion was significantly higher in group I than in group II, although post-transplant left ventricular function was similar in both groups. Although there was no difference in cardiac function after implantation, donor hearts should be arrested by extracellular-type cardioplegia to prevent coronary vasoconstriction associated with preservation in University of Wisconsin solution.     

The effectiveness of ischemic preconditioning on myocardial protection and comparison with K(+) cardioplegia

The purpose of this study is to investigate the effects of ischemic preconditioning on myocardial protection and to compare this method to K(+) crystalloid cardioplegia. Langendorff perfused isolated working rat hearts were used in the following groups. After 20 min of stabilisation, 30 hearts were divided into three groups. In group I (control, n=10), hearts were arrested with cold (+4 degrees C) Krebs-Henseleit (K-H) solution, in group II (cardioplegia, n=10) hearts were arrested with cold K(+) cardioplegia solution, and in group III (preconditioning, n=10) hearts were subjected to 5 min normothermic ischemia followed by 5 min reperfusion then arrested with cold K-H solution. All hearts were subjected to 30 min of global ischemia (24 degrees C) and 40 min of reperfusion. Hemodynamic measurements were performed with a left ventricular latex balloon using a data acquisition system. Creatine kinase (CK-MB) washout and Troponin I (cTnI) levels were determined from the coronary effluents. There was no significant difference among the three groups in any of the parameters (hemodynamic and biochemical) measured at the end of stabilisation period. During reperfusion, functional recovery and coronary flow were significantly improved in K(+) cardioplegia and preconditioned groups compared with control group. CK-MB washout and cTnI levels were significantly lower in groups II and III compared with group I at the reperfusion. However no significant difference was observed between K(+) cardioplegia and preconditioned groups among biochemical and hemodynamic parameters and coronary flow at the post-ischemic period. In conclusion, ischemic preconditioning is as effective as K(+) cardioplegia on myocardial protection and recovery of myocardial function during reperfusion.     

Heart preservation in HTK solution: role of coronary vasculature in recovery of cardiac function

BACKGROUND: Poor myocardial tolerance to prolonged cold ischemia remains a major concern in heart transplantation. In this study, we estimated superiority of Histidine-Tryptophan-Ketoglutarate (HTK) over University of Wisconsin (UW) as a cardiac preservation solution. METHODS: Isolated rat hearts were mounted on a Langendorff apparatus to estimate the baseline cardiac function. The hearts were arrested and stored at 4 degrees C in UW and HTK solution for 8 hours, and then reperfused. The aortic flow, coronary flow, cardiac output, rate pressure product, and left ventricular dp/dt in the HTK group recovered significantly more than the UW group. The values of myocardial total adenine nucleotides and the adenosine triphosphate to adenosine diphosphate ratio were higher in the HTK than in the UW group. We also examined coronary vascular responsiveness using left coronary arteries dissected from the rat hearts before flushing, before storage, after storage, and after reperfusion. RESULTS: The maximal relaxation response to acetylcholine was significantly higher in the HTK than in the UW group after reperfusion, although there were no significant differences at each stage before reperfusion. In addition, the endothelium-independent relaxation response to sodium nitroprusside in the HTK group was also well preserved after reperfusion. CONCLUSIONS: These results indicate that HTK is superior to UW solution for cardiac preservation. HTK protects coronary vasculature during preservation, which together with reperfusion might lead to improved functional cardiac recovery following preservation.     

Preclinical evaluation of coronary vascular function after cardioplegia with HTK and different antioxidant additives.

OBJECTIVE: Due to limited resources, improvement of preservation solutions is still of great importance in cardiac transplant surgery. New additives with antioxidant properties were tested with respect to coronary function of isolated rat hearts. METHODS: Bretschneider HTK solution containing none or an antioxidant additive (deferoxamine, trolox or LK 616) was used for 8h cold cardioplegia. After reperfusion with Krebs-Henseleit buffer (KHB), we assessed vascular dilator capacity (bradykinin, adenosine triphosphate, reactive hyperemia), myocardial function (left ventricular developed pressure, heart rate, oxygen consumption) and release of biochemical markers (aspartate aminotransferase, creatine kinase, lactate dehydrogenase, troponin, adenosine). RESULTS: Bradykinin- and adenosine triphosphate-induced vasodilations were largely reduced in hearts stored 8h in traditional HTK as compared to unstored controls. Storage in HTK+LK 616 significantly improved bradykinin-induced vasodilation. Vasodilation toward ATP was best preserved in hearts stored in HTK+deferoxamine. Deferoxamine and trolox, both improved reactive hyperaemic response during reperfusion. Left ventricular pressure development was significantly reduced after 8h cardioplegia, but no difference existed between different cardioplegia groups. Release of biochemical markers of tissue injury was similar in all cardioplegia groups. After storage in HTK+LK 616 (100 microM), however, heart marker release was slightly augmented as compared to HTK. CONCLUSIONS: Despite similar myocardial function and marker release, coronary vascular function after cardioplegic storage may profit by addition of iron chelators (or antioxidants) to traditional HTK solution.     

Calcium paradox in an in vivo model of multidose cardioplegia and moderate hypothermia. Prevention with diltiazem or trace calcium levels

The production and prevention of calcium paradox injury in myocardium was studied in a canine model of cardiopulmonary bypass with multidose, moderately hypothermic, crystalloid cardioplegic solution. During 4 1/2 hours of global ischemia, three groups of six dogs each received one of three histidine-buffered cardioplegic solutions (500 ml initially and 250 ml every 30 minutes) at 27 degrees C. Group 1 cardioplegic solution was calcium free, group 2 solution contained a trace amount of calcium chloride (70 mumols /L), and group 3 cardioplegic solution was calcium free but contained diltiazem (150 micrograms/kg body weight). Left ventricular function measured as percent control of developed pressure revealed significantly greater (p less than 0.05) recovery in groups 2 and 3. Triphenyltetrazolium chloride staining showed 35% +/- 9% (mean +/- standard error) of heart mass necrosis in group 1 versus 0% and 0.5% +/- 0.4% in groups 2 and 3, respectively (p less than 0.001). Electron microscopy revealed ultrastructural changes characteristic of calcium paradox injury in group 1 myocardium. Calcium paradox injury was produced in an in vivo model of global myocardial ischemia and multidose cardioplegia despite moderate hypothermia and non-coronary collateral flow. The addition of either trace levels of calcium or diltiazem to the cardioplegic solution was effective in preventing this injury.     

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.     

Orthotopic transplantation of pig hearts harvested after 30 min of normothermic ischemia: controlled reperfusion with blood cardioplegia containing the Na-H-exchange inhibitor HOE 642

Objectives: The aim of our study was to develop a surgical technique for a successful transplantation of hearts harvested after 30 min of normothermic ischemia without donor pretreatment. Successful transplantation of ischemic compromised hearts could help to expand the severely limited donor pool. We used the pig model because this species is very susceptible to myocardial ischemia. Na⁺-H⁺-exchange (NHE) inhibitors have shown excellent protective properties in several in vitro and in vivo models of myocardial ischemia and reperfusion. Methods: In group I (n=12) hearts were harvested after 30 min of normothermic ischemia following cardiac arrest induced by exsanguination. Hearts were perfused with warm blood cardioplegia and transplanted orthotopically. In group II (n=9) controlled reperfusion with cold leucocyte-depleted blood cardioplegia was performed after 30 min of normothermic ischemia. In group III (n=8) the same procedure was performed as in group II but blood cardioplegia contained 1 mmol/l HOE 642. Results: In group I massive myocardial oedema was observed and none of the animals could be weaned from cardiopulmonary bypass (CPB). In contrast, all animals in groups II and III could be weaned from CPB with low dose inotropic support. In groups II and III the contractility of the hearts, expressed as maximal left and right ventricular stroke work index was significantly impaired after transplantation as compared with the preoperative value. Supplementation of blood cardioplegia with HOE 642 resulted in a significantly better recovery of the LVSWImax (Group II vs. III). Conclusions: Successful transplantation of pig hearts is possible after 30 min of normothermic ischemia without donor pretreatment if a controlled reperfusion with cold leucocyte-depleted blood cardioplegia is performed. HOE 642 given during reperfusion only improves posttransplant left ventricular function.     

Interrelated effects of nucleoside mono- and triphosphates and phosphoenolpyruvate on rat hearts subjected to cardioplegic arrest at normothermia

Supplementation with phosphoenolpyruvate (PEP) and ATP was previously found to enhance the protective effect of potassium cardioplegia on rat hearts subjected to extensive ischemic trauma (30 min at 37 degrees C) in the paracorporeal rat heart model. In the present experiments, the ischemia time was reduced to 20 min (37 degrees C). Ventricular work after ischemia was best in control rats with potassium cardioplegia only. Supplementing the cardioplegic solution with PEP and ATP (group I) resulted in significantly reduced postischemic ventricular work and increased efflux of the creatine kinase isoenzyme MB (CK-MB). The same result was obtained when adenosine monophosphate (AMP) was added to the supplementation (group II). When guanosine monophosphate (GMP) was added instead of AMP (group III), the negative effects of PEP and ATP in the cardioplegic solution were partly abolished. Plain potassium cardioplegia, without additives, nevertheless gave the best results. There were no significant intergroup differences in the myocardial content of adenine nucleotides. The results contrasted with those in the previous study of more protracted ischemic trauma (30 min at 37 degrees C) and possible explanations are discussed.     

Effects of supplemental L-arginine during warm blood cardioplegia.

OBJECTIVES: Effects of supplemental L-arginine, nitric oxide precursor, during warm blood cardioplegia were assessed in the blood perfused isolated rat heart. METHODS: The isolated hearts were perfused with blood at 37 degrees C from a support rat. After 20 minutes of aerobic perfusion, the hearts were arrested for 60 minutes with warm blood cardioplegia given at 20-minute intervals. This was followed by 60 minutes of reperfusion. The hearts were divided into the following three groups according to the supplemental drugs added to the cardioplegic solution. The control group (n = 10) received standard warm blood cardioplegia. The L-ARG group (n = 10) received warm blood cardioplegia supplemented with L-arginine (3 mmol/l). The L-NAME group (n = 10) received warm blood cardioplegia supplemented with L-arginine (3 mmol/l) and L-nitro-arginine methyl ester, a competitive inhibitor of nitric oxide synthase (1 mmol/l). After 60 minutes of cardioplegic arrest, cardiac function, myocardial metabolism and myocardial release of circulating adhesion molecules were measured during reperfusion. RESULTS: Left ventricular end-diastolic pressure was significantly lower (p<0.05) in the L-ARG group than in the control group and the L-NAME group during reperfusion. Isovolumic left ventricular developed pressure, dp/dt and coronary blood flow were significantly greater (p< 0.05) in the L-ARG group during reperfusion. The L-ARG group resulted in early recovery of lactate metabolism during reperfusion. Myocardial release of circulating intercellular adhesion molecule-1 (ICAM-1) and E-selectin were significantly less (p<0.05) in the L-ARG group at 15 minutes of reperfusion. CONCLUSIONS: The results suggest that augmented nitric oxide by adding L-arginine to warm blood cardioplegia can preserve left ventricular function and ameliorate endothelial inflammation. The technique can be a novel cardioprotective strategy in patients undergoing cardiac surgery.     

Cariporide对未成熟兔心肌缺血再灌注损伤的保护作用

目的　探讨甲磺酸苯甲酰胍类化合物Cariporide对未成熟兔心肌缺血再灌注损伤的保护作用及其机制。　方法　以离体灌注幼兔心脏为模型 ,将 2 4只幼兔心脏随机均分为对照组 (应用St.ThomasⅡ液 )和实验组 (应用Cariporide St .ThomasⅡ液 ) ,常温缺血 60min ,期间每 2 0min灌注 1次保护液 ,恢复灌注后 ,测定心率、心律、平均动脉压、冠脉流量、左心室收缩压、左心室舒张末压、左心室压力微分 (±dp/dt)和心肌酶。将另 6只幼兔的心肌单细胞悬液随机均分为基础 (未予缺氧处理 )、钙对照和钙实验组 (经缺氧、再复氧处理 ,钙实验组于缺氧时加入Cariporide 1μmol/L) ,用激光共聚焦显微镜测定心肌细胞内游离钙 ([Ca2 ]i)浓度 ,以钙荧光强度比值表示。　结果　与对照组相比 ,实验组缺血、再灌注后室颤发生率低 ,心肌酶漏出量少 ,平均动脉压、左心室收缩压、冠脉流量及±dp/dt均明显增加 ,左心室舒张压低。未成熟兔心肌细胞内 [Ca2 ]i浓度 ,钙实验组比钙对照组明显减少 (P <0 0 1) ,钙实验组与基础组差异无显著意义 (14 4 6± 12 8与 13 75± 10 2 ,P >0 0 5)。结论　Cariporide对未成熟心肌缺血再灌注损伤有保护作用 ,其机制是抑制心肌细胞内 [Ca2 ]i超载引起的缺血再灌注损伤     

Prevention of reperfusion injury in ischemic-reperfused hearts by oxypurinol and allopurinol

We investigated the effects of the xanthine oxidase inhibitor allopurinol and its metabolite oxypurinol on isolated rabbit hearts. To assess the potential role of these drugs in preventing reperfusion injury, hearts were perfused using Langendorff techniques, held globally ischemic for 3 h at 15°C, and then reperfused. During perfusion, hearts received Krebs-Henseleit solution maintained at 37°C. Aortic perfusion pressure was held constant at 80 cm H₂O. Prior to ischemia, hearts were arrested with a constant volume of KCl cardioplegia. Using a left ventricular (LV) balloon, developed pressures were measured prior to and following global ischemia. In addition, coronary circulation (CC) was measured before and after ischemia. All hearts were paced at 260 beats/min. We studied four groups: group 1 received 1 mM allopurinol, group 2 received 1 mM oxypurinol, group 3 received 90 IU/ml superoxide dismutase (SOD) plus 8085 IU/ml catalase (CAT), and group 4 received no treatment and served as a control. Each group consisted of 8 animals. Hearts receiving drug treatment did so during the first 5 min of reperfusion. Displaying all data as a function of LV volume, postischemic values were compared to preischemic values. Multivariate analysis and Tukey tests were used to detect significant differences between groups. When compared to the control group, all drug-treated groups significantly recovered end-diastolic function. Peak systolic pressure decreased significantly in the SOD/CAT group as compared to all other groups. LV isovolumetric work decreased significantly more in the SOD/CAT and control groups than in the oxypurinol group. Coronary circulation decreased significantly in the SOD/CAT and control groups as compared to the allopurinol and oxypurinol groups. Our results demonstrate an enhanced recovery of function when oxypurinol and allopurinol are given at the time of reperfusion. Recent evidence has supported the view that rabbit myocardium, as well as human myocardium, lacks xanthine oxidase. The beneficial effects seen with these drugs may therefore be unrelated to the presence of xanthine oxidase.     

Nicardipine: myocardial protection in isolated working hearts.

The effectiveness of the calcium antagonist nicardipine in protecting the ischemic myocardium was evaluated using the hemodynamic recovery of isolated working rat hearts subjected to hyperkalemic cardiac arrest followed by ischemia at 37.5 degrees C and 10 degrees C. Rat hearts (n = 51) received 20 mL of cardioplegia and were subjected to 27 minutes of ischemia at 37.5 degrees C. Group A (control) did not receive nicardipine. Groups B through F received nicardipine in the cardioplegia with total doses ranging from 2 micrograms to 6 micrograms. Group A had 46% survival of ischemia, whereas groups C (3 micrograms) and D (4 micrograms) had survival rates of 88% and 100%, respectively (p less than 0.05). The recovery of aortic flow after ischemia was 35% in group A, compared with 76% in group B (2 micrograms) and 81% in group D (p less than 0.05). Group A had 49% postischemic recovery of cardiac output, whereas groups B and D had 82% and 85% recovery (p less than 0.05). The postischemic recovery of stroke volume was 48% in group A compared with 84% in group B, 87% in group D, and 73% in group E (5 micrograms) (p less than 0.05). Additional rats were exposed to 210 minutes of ischemia (n = 41) or 240 minutes of ischemia (n = 56) at 10 degrees C. Control groups did not receive nicardipine, whereas treatment groups received nicardipine in the cardioplegia with total doses ranging from 1.4 micrograms to 6.4 micrograms. There were no significant differences in the survival of ischemia or the recovery of function after ischemia at 10 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)     

Adenosine-enhanced ischemic preconditioning provides enhanced cardioprotection in the aged heart

Background. Recently we have reported a novel myoprotective protocol “adenosine-enhanced ischemic preconditioning” (APC), which extends and amends the protection afforded by ischemic preconditioning (IPC) by both reducing myocardial infarct size and enhancing postischemic functional recovery in the mature rabbit heart. However, the efficacy of APC in the senescent myocardium was unknown.

Methods. The efficacy of APC was investigated in senescent rabbit hearts and compared with magnesium-supplemented potassium cardioplegia (K/Mg) and IPC. Global ischemia (GI) hearts were subjected to 30 minutes of global ischemia and 120 minutes of reperfusion. Ischemic preconditioning hearts received 5 minutes of global ischemia and 5 minutes of reperfusion before global ischemia. Magnesium-supplemented potassium cardioplegia hearts received cardioplegia just before global ischemia. Adenosine-enhanced ischemic preconditioning hearts received a bolus injection of adenosine in concert with IPC. To separate the effects of adenosine from that of APC, a control group (ADO) received a bolus injection of adenosine 10 minutes before global ischemia.

Results. Infarct size was significantly decreased to 18.9% ± 2.7% with IPC (p < 0.05 versus GI); 17.0% ± 1.0% with ADO (p < 0.05 versus GI); 7.7% ± 1.3% with K/Mg (p < 0.05 versus GI, IPC, and ADO); and 2.1% ± 0.6% with APC (p < 0.05 versus GI, IPC, ADO, and K/Mg; not significant versus control). Only APC and K/Mg significantly enhanced postischemic functional recovery (not significant versus control).

Conclusions. Adenosine-enhanced ischemic preconditioning provides similar protection to K/Mg cardioplegia, significantly enhancing postischemic functional recovery and decreasing infarct size in the senescent myocardium.