Amelioration of reperfusion injury following hypothermic, ischemic cardioplegia in isolated, infarcted rat hearts

The left coronary artery was ligated and myocardial infarction developed in 28 rats. Three weeks later, the hearts were excised and mounted in an apparatus for perfusion of non-working isolated hearts (Langendorff). Hypothermic (15 degrees C), ischemic cardioplegia was induced for either 2 or 3 1/2 h followed by reperfusion for 45 min. Half of the hearts were reperfused with an initially gradual rise in temperature and pressure of the perfusion fluid, whereas the other half was reperfused directly with the perfusate at 37 degrees C and 100 cm H2O pressure. The hearts were examined by transmission electron microscopy and randomized for stereological analysis based on point counting on electron micrographs. Cardioplegia of 2 h duration was tolerated better than cardioplegia for 3 1/2 h (interstitial edema; P = 0.03, fraction of altered mitochondria; P = 0.001). Particularly in the hearts undergoing the longest cardioplegia, myocardial injury was less severe following a gentle reperfusion as compared with those exposed to the clinically common abrupt technique (fraction of mitochondria in the myocyte; P = 0.03, fraction of altered mitochondria; P = 0.008). In the interstitium, the luminal area of capillaries was significantly increased and the endothelial swelling less pronounced in the groups undergoing the gentle reperfusion technique, (luminal/endothelial fraction; P = 0.01). The study shows that previously infarcted hearts are susceptible to ischemic damage even after 2 h of regular hypothermic, ischemic cardioplegia and that a gentle reperfusion technique significantly ameliorates reperfusion injury.     

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.     

Myocardial oxygen consumption and lactate production during antegrade warm blood cardioplegia.

Continuous warm blood cardioplegia has recently been recommended as an alternative to multidose cold blood cardioplegia for myocardial protection during coronary bypass operations. Cardioplegia may have to be interrupted in order to provide a bloodless operating field during coronary anastomosis. To determine the effects of ischemia at normothermia on myocardial oxygen consumption and lactate production we randomized 17 dogs to receive either warm blood cardioplegia (37 degrees C) or cold blood cardioplegia combined with systemic and topical cooling. After initiating arrest, cardioplegia was interrupted for periods of 1, 2, 3, 4, 5, 6, and 10 min. Myocardial oxygen debt occurred after 3.5 min of ischemia in the 9 animals receiving warm blood cardioplegia. In contrast, myocardial oxygen consumption never exceeded oxygen availability during cold blood cardioplegia (P less than 0.001). Lactate production increased linearly in both groups but was much greater in those animals receiving warm blood cardioplegia (P less than 0.001). Spontaneous electromechanical activity was much more common during warm blood cardioplegia which required frequent infusions of cardioplegia to maintain cardiac arrest (P less than 0.0003). Conclusions: (1) Oxygen debt occurred after 3.5 min of warm ischemia; (2) spontaneous electromechanical activity is more common during warm heart protection which necessitates the use of larger volumes of cardioplegia to maintain cardiac arrest.     

温血停搏液术终灌注对缺血再灌注心肌的保护作用

利用猫体外循环模型观察含甘露醇的温血停搏液术终灌注对缺血再灌注心肌的保护作用。心肌缺血恢复正常血液灌注前，从主动脉根部以５～６ｋＰａ的压力注入３７℃含甘露醇的低钾温血停搏液５０ｍｌ。结果显示用含甘露醇的温血停搏液术终灌注可保护缺血后再灌注心肌的功能，提高心肌能量储备，降低线粒体丙二醛含量。结论：含甘露醇的温血停搏液术终灌注，可提高心肌对氧自由基的清除能力，减轻线粒体膜脂质过氧化，提高心肌能量储备，有利于再灌注后心肌功能的恢复     

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.     

Warm retrograde blood cardioplegia saves more ischemic myocardium but may cause a functional impairment compared to cold crystalloid.

OBJECTIVES: Ongoing ischemia, or even ischemia in progress, is regularly encountered in today's patients amenable to cardiac surgery. We set out to assess the effect of 'active resuscitation' during cardioplegia with warm continuous retrograde blood cardioplegia (WB) in a protocol simulating a clinical situation. METHODS: After 60 min with a regional ischemic injury to the left ventricle, 21 pigs were randomized to receive no treatment (control), cold retrograde intermittent crystalloid cardioplegia (CC) or WB. All animals were put on cardiopulmonary bypass. After 1h of cardioplegia and 1 h of reperfusion the perfused left ventricle was colored with methylene blue. After excision of the hearts a standard planimetri technique was used to determine the area at risk and amount of necrosis (triphenyltetrazolium). Heart rate, mean arterial pressure (MAP), cardiac output and myocardial blood flow were recorded as well as myocardial oxygen consumption, plasma levels of free fatty acids, glucose, lactate and Troponin T from the coronary sinus. RESULTS: The area at risk of the left ventricle was 13.6+/-1.2%. We found 71+/-2, 61+/-3 and 30+/-2% necrosis of the area at risk in the controls, CC and WB, respectively (P<0.001, CC versus control and P<0.0001, WB against CC and control). Troponin T release was highest in the CC group in the reperfusion period. Glucose levels increased significantly after ischemia in the controls and WB. In accordance with the amount of saved myocardium in the WB group which also had a normal coronary sinus lactate level as opposed to the fourfold increase in the CC group after ischemia. After standstill cardiac output and MAP were significantly lower than baseline values in the WB group only (P<0.05). CONCLUSIONS: CC did reduce the size of the infarction by about 10% compared to control animals, whereas WB reduced the infarction by more than 50% of that seen after CC. Both modalities are, however, associated with a functional reduction during the first 60 min of reperfusion, WB being the worst.     

Captopril improves oxygen and glucose extraction in pig hearts during reperfusion after cold cardioplegic storage

The purpose of this study was to evaluate the haemodynamic and metabolic effects of captopril during reperfusion of pig hearts following 360 min global hypothermic cardioplegia and storage (HCS). The hearts were perfused with one litre of cold crystalloid cardioplegia (Bretschneider solution no. 3), excised and stored in saline at 4 degrees C for 360 min. The hearts were then reperfused with blood in a modified Langendorff model for 60 min. Left ventricular function, myocardial blood flow, and arteriovenous differences in oxygen, glucose and lactate were monitored intraoperatively and during reperfusion. Two groups of hearts were studied. Group I (captopril treated, n = 9): the pigs were pre-medicated with increasing oral doses of captopril for 3 weeks (12.5 mg-150 mg daily) and an intravenous dose (25 mg) upon arrival at the laboratory. Captopril was added to the cardioplegia (1000 microg/l) and to the reperfusion media (1000 microg/l). Group II (controls, n = 8): the pigs were given no premedication, captopril-free cardioplegia and the hearts were reperfused with captopril-free blood. Captopril increased myocardial oxygen and glucose extraction during reperfusion (p < 0.05 for both) while lactate remained unchanged after 360 min HCS. Treatments with captopril increased developed left ventricular pressure (DLVP) and relaxation (-dP/dtmax) during reperfusion (p < 0.05 for both), while contractility (+dP/dtmax) was unchanged. Heart rate was reduced in captopril-treated hearts (p < 0.05) while myocardial blood flow (MBF) was similar in the two groups. Captopril administration prior to and during HCS and postcardioplegic reperfusion improves oxygen and glucose extraction in large spontaneously beating porcine hearts during reperfusion. The underlying mechanisms seem to involve metabolic modulation, since myocardial uptake of oxygen and glucose was increased in the absence of changes in myocardial blood flow.     

Intermittent warm blood cardioplegia does not provide adequate myocardial resuscitation after global ischaemia.

OBJECTIVE: Intermittent warm blood cardioplegia is controversial, and many surgeons consider it inadequate for myocardial protection. The purpose of this study was to compare intermittent and continuous warm blood cardioplegia as resuscitation in hearts exposed to global ischaemia. METHODS: Pigs were put on cardiopulmonary bypass (CPB) and subjected to 30 min of warm, "unprotected", global ischaemia, followed by continuous (n = 7) or intermittent (n = 10, 12 ml/kg every 10 min) warm (34 degrees C) antegrade blood cardioplegia for 45 min (delivery pressure 75-80 mmHg) and weaned from CPB 45 to 60 min later. Indices of left ventricular function were acquired with the conductance catheter technique and pressure-volume loops at baseline and after 90 min of reperfusion. RESULTS: Cardioplegia was delivered during 17% of the cross-clamp time. Global left ventricular function, evaluated by preload recruitable stroke work (PRSW), was unchanged after continuous cardioplegia; 95 (76-130) (median (quartile interval)) to 91 (90-104) erg/ml x 10(3), but decreased after intermittent cardioplegia; 122 (100-128) to 64 (23-93) erg/ml x 10(3). Two pigs in the intermittent group weaned from CPB, but died before post-bypass measurement. A 95% confidence interval for the difference in post-bypass mean PRSW was estimated as 32 +/- 30 erg/ml x 10(3) (corresponding to P = 0.04 for comparison between treatments). The end-diastolic pressure-volume relation (EDPVR) increased from 0.17 (0.14-0.20) (continuous) and 0.15 (0.12-0.22) (intermittent) mmHg/ml to 0.27 (0.22-0.33) (P = 0.018) and 0.39 (0.25-0.66) (P = 0.005) mmHg/ml, respectively, indicating deterioration in diastolic function. No difference between groups was found in EDPVR, stiffness constant, troponin T release or myocardial water content. CONCLUSION: Following acute global ischaemia left ventricular global function was, in this model, less preserved using warm intermittent compared to warm continuous cardioplegia.     

The effect of controlled reperfusion in porcine hearts submitted to three hours of cold global ischemia

Abstract. At present, many investigations of myocardial function following ischemic insults concentrate on the modalities of reperfusion rather than on the mode of preservation. In this study, we tried to define the effect of reperfusion using warm blood cardioplegia (WBC) after medium-term (3 h) cold global ischemia, as required in cardiac transplantation. Twenty-one porcine hearts were harvested after preservation with cold cardioplegia (St. Thomas Hospital solution) and topical cooling. Normothermic reperfusion with blood was initiated after 3 h of ischemia utilizing a special extracorporeal pump circuit. Twelve hearts served as controls (group A), while substrate-enriched WBC was applied during the initial 20 min of reperfusion in nine hearts (group B). Hearts in both groups were then studied for myocardial function and metabolism under both working and nonworking conditions for a maximum of 180 min. In the nonworking mode, left ventricular dp/dt was significantly higher in group B than in group A at 15 min (2201 ± 785 mm Hg/sec vs 1515 ± 732 mm Hg/sec) and at 180min (1730 ± 471 mm Hg/sec vs 836 ± 147 mm Hg/sec; P <0. 05). After 3 h, lactate production was significantly higher in group A (371 ± 45mg/dl) than in group B (108 ± 44 mg/dl; P < 0. 05). Creatine kinase release into the coronary sinus was also significantly elevated in group A at-15min (2807 ± 1478 IU/l vs 1148 ± 1272 IU/l; P < 0. 05). Similarly, the hemodynamic data obtained under working conditions in group B were superior to those in group A. We conclude that following 3 h of cold global ischemia, reperfusion with WBC improves myocardial function and metabolism. Cautious application in clinical heart transplantation is recommended.     

Activation of myocardial constitutive nitric oxide synthase during coronary artery surgery.

OBJECTIVE: The role of nitric oxide (NO) in myocardial ischemia/reperfusion is controversial. While some studies have shown cardioprotective effects of NO, others suggested that increased myocardial NO release secondary to ischemia may contribute to reperfusion injury. However, the impact of cardioplegia-induced myocardial ischemia/reperfusion on the activity of the NO-producing enzyme constitutive NO-synthase (cNOS or NOS-III) has not been investigated. METHODS: Twenty elective CABG patients were randomized to receive myocardial protection using either intermittent cold blood cardioplegia with 'hot-shot' (CBC; n=10) or continuous warm blood enriched with the ultra-fast-acting beta-blocker esmolol (WBE; n=10). We collected transmural LV biopsies prior to cardiopulmonary bypass (CPB), at the end of the cross-clamp period, and at the end of CPB. Specimen were subjected to immunocytochemical staining against myocardial NOS-III and cGMP using polyclonal antibodies. NOS-III activity was determined using TV-densitometry (gray units) and cGMP content using a semiquantitative score. Global myocardial metabolism was assessed by arterio-coronary sinus lactate concentration difference (a-csD(LAC)). For LV function determination we measured the fractional area of contraction (FAC) using TEE. RESULTS: In CBC hearts a-csD(LAC) was significantly decreased following cross-clamp removal as compared to pre-CPB indicating global ischemia during cross-clamp. In contrast, a-csD(LAC) was unchanged in WBE hearts indicating absence of relevant ischemia in this group. In CBC hearts NOS-III activity did not change from pre-CPB (35.6+/-11.1 U) to the end of the cross-clamp period (38. 0+/-8.1 U; P=0.2), but increased significantly to 48.5+/-12.1 U at the end of CPB following initial warm blood reperfusion (P=0.026). In WBE hearts NOS-III activity remained unchanged throughout (29. 2+/-10.8, 35.1+/-11.8, and 32.2+/-14.7 U, respectively; 0.3). At the end of CPB, nine CBC hearts, but only one WBE heart showed increased cGMP content (P=0.002). Compared to pre-CPB, FAC in the CBC group was 109+/-25% following weaning off CPB (P=0.26), but was slightly decreased to 87+/-22% at 4 h post-CPB (P=0.03). In the WBE group FAC remained unchanged compared to pre-CPB throughout (103+/-21 and 96+/-37%, respectively; 0.5). CONCLUSIONS: Our data show that global myocardial ischemia and reperfusion induced by CBC is associated with myocardial NOS-III activation and increased cGMP content suggesting increased NO release. In contrast, avoidance of ischemia by use of WBE prevented NOS-III and c-GMP increase. As LV function was decreased at 4 h post-CPB in the CBC group, these data suggest that increased NO release secondary to NOS-III activation may have contributed to ischemia-reperfusion injury as has been shown experimentally.     

Leukocyte-depleted reperfusion of transplanted human hearts prevents ultrastructural evidence of reperfusion injury.

The present study examines whether leukocyte depletion can prevent postreperfusion ultrastructural injury in transplanted human hearts. Thirty-two patients undergoing orthotopic cardiac transplantation were randomized to receive either enriched, warm, whole blood (Group I; n = 16) or enriched, warm, leukocyte-depleted blood (Group II; n = 16) reperfusion. Donor hearts were arrested with 1 liter of 4 degrees C crystalloid cardioplegia and topically cooled. RV endomyocardial biopsies taken at end-ischemia and following reperfusion were assessed in a blinded fashion and graded according to injury (1 = minimal to 4 = severe). The mean ischemic time (Group I = 142 min, Group II = 153 min) was similar in the two groups. End-ischemic biopsies showed mild-moderate interstitial edema and mild capillary endothelial swelling in both groups with similar injury scores (Group 1 = 1.3 +/- 0.09 (means +/- SEM), Group 2 = 1.25 +/- 0.08). Postreperfusion biopsies in Group I showed nuclear chromatin clumping, moderate mitochondrial swelling, marked capillary endothelial swelling, and marked interstitial edema with a grade of 2.6 +/- 0.14 (P less than 0.001, paired t test). In contrast, postreperfusion biopsies in Group II showed minimal changes with a grade of 1.33 +/- 0.09, P less than 0.0001 in comparison to Group I Leukocyte-depleted reperfusion of human transplanted hearts prevents ultrastructural injury. This may allow safe extension of the ischemic period and result in improved graft function.     

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.     

Influence of pre-existing ischemia on recovery from chemical cardioplegia. A study on pig hearts in an isolated blood-perfused model.

The impact of prior cardiac ischemia on recovery from chemical cardioplegia was investigated in pig hearts. Group I hearts were subjected to 9-min normothermic ischemia before the start of chemical cardioplegia. After 180 min of induced cardiac arrest, all hearts were reperfused and monitored for 120 min in a blood-perfused Langendorff model. Consistent with left ventricular performance, myocardial oxygen uptake was significantly lower in group I than in the other hearts during the first 60 min of reperfusion. Lactate elimination was significantly higher in group I at the start of reperfusion, but showed no intergroup difference after 25 min. Nor was intergroup difference found in left ventricular end-diastolic pressure, total myocardial flow or glucose extraction fraction during reperfusion. The mitochondrial ultrastructure was identical in the two groups before chemical cardioplegia. During cardioplegia it deteriorated in group I but normalized in group II. During reperfusion these circumstances were reversed. Although precardioplegic ischemia thus significantly impaired left ventricular performance during early recovery, with corresponding effects on metabolism and ultrastructure, stable performance during reperfusion indicated that the ischemic injury did not worsen.     

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.     

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.     

Protein kinase C isoform-dependent myocardial protection by ischemic preconditioning and potassium cardioplegia

OBJECTIVE: Ischemic preconditioning combined with potassium cardioplegia does not always confer additive myocardial protection. This study tested the hypothesis that the efficacy of ischemic preconditioning under potassium cardioplegia is dependent on protein kinase C isoform. METHODS: Isolated and crystalloid-perfused rat hearts underwent 5 cycles of 1 minute of ischemia and 5 minutes of reperfusion (low-grade ischemic preconditioning) or 3 cycles of 5 minutes of ischemia and 5 minutes of reperfusion (high-grade ischemic preconditioning) or time-matched continuous perfusion. These hearts received a further 5 minutes of infusion of normal buffer or oxygenated potassium cardioplegic solution. The isoform nonselective protein kinase C inhibitor chelerythrine (5 micromol/L) was administered throughout the preischemic period. All hearts underwent 35 minutes of normothermic global ischemia followed by 30 minutes of reperfusion. Isovolumic left ventricular function and creatine kinase release were measured as the end points of myocardial protection. Distribution of protein kinase C alpha, delta, and epsilon in the cytosol and the membrane fractions were analyzed by Western blotting and quantified by a densitometric assay. RESULTS: Low-grade ischemic preconditioning was almost as beneficial as potassium cardioplegia in improving functional recovery; left ventricular developed pressure 30 minutes after reperfusion was 70 +/- 15 mm Hg (P <.01) in low-grade ischemic preconditioning and 77 +/- 14 mm Hg (P <.001) in potassium cardioplegia compared with values found in unprotected control hearts (39 +/- 12 mm Hg). Creatine kinase release during reperfusion was also equally inhibited by low-grade ischemic preconditioning (18.2 +/- 10.6 IU/g dry weight, P <.05) and potassium cardioplegia (17.6 +/- 6.7 IU/g, P <.01) compared with control values. However, low-grade ischemic preconditioning in combination with potassium cardioplegia conferred no significant additional myocardial protection; left ventricular developed pressure was 80 +/- 17 mm Hg, and creatine kinase release was 14.8 +/- 11.0 IU/g. In contrast, high-grade ischemic preconditioning with potassium cardioplegia conferred better myocardial protection than potassium cardioplegia alone; left ventricular developed pressure was 121 +/- 16 mm Hg (P <.001), and creatine kinase release was 8.3 +/- 5.8 IU/g (P <.05). Chelerythrine itself had no significant effect on functional recovery and creatine kinase release in the control hearts, but it did inhibit the salutary effects not only of low-grade and high-grade ischemic preconditioning but also those of potassium cardioplegia. Low-grade ischemic preconditioning and potassium cardioplegia enhanced translocation of protein kinase C alpha to the membrane, whereas high-grade ischemic preconditioning also enhanced translocation of protein kinase C delta and epsilon. Chelerythrine inhibited translocation of all 3 protein kinase C isoforms. CONCLUSIONS: These results suggest that myocardial protection by low-grade ischemic preconditioning and potassium cardioplegia are mediated through enhanced translocation of protein kinase C alpha to the membrane. It is therefore suggested that activation of the novel protein kinase C isoforms is necessary to potentiate myocardial protection under potassium cardioplegia.     

Myocardial neutrophil sequestration during reperfusion of the transplanted rabbit heart.

BACKGROUND: Neutrophils are major participants in myocardial reperfusion injury, but the relationship between ischemic time and the extent of the neutrophil sequestration in heart transplantation has not yet been systematically studied. This study was designed to determine whether increased ischemic time would cause greater neutrophil sequestration during reperfusion of the globally ischemic heart. METHODS: Rabbit hearts were arrested with cardioplegia, explanted, and subjected to either 1 or 4 hours of global ischemia at 4 degrees C before being heterotopically transplanted into a recipient rabbit's abdomen for reperfusion. Each heart was reperfused for either 4, 8, or 12 hours. Between 3 and 7 hearts were studied (average = 5.8) for each combination of ischemic and reperfusion time (total = 35). A myeloperoxidase (MPO) assay was used to qualify neutrophil content. RESULTS: MPO activity (U/g wet weight) was not significantly different at 4, 8, and 12 hours of reperfusion (0.33 +/- 0.05, 0.20 +/- 0.04, 0.26 +/- 0.04: p = 0.13), but was significantly increased at 4 hours compared to 1 hour ischemia (0.34 +/- 0.04 vs 0.19 +/- 0.03: p = 0. 006). Interaction between ischemic and reperfusion times was not significant (p = 0.12). MPO activity was below the measurable threshold in 5 freshly excised control hearts. CONCLUSIONS: These results suggest that acute reperfusion injury will be more severe in the hearts subjected to 4 hours ischemia and indicate the need to consider neutrophil-mediated reperfusion injury when addressing cardioprotective interventions for cardiac preservation and reperfusion after transplantation. Neutrophil-mediated reperfusion injury of the rabbit myocardium after heterotopical transplantation is more severe in hearts subjected to 4 hours of ischemia vs 1 hour of ischemia prior to transplantation.     

Does adenosine administration during the early reperfusion period affect ischemic preconditioning?

We hypothesized that the adenosine administration during the early reperfusion period might affect ischemic preconditioning (IPC) and might reduce infarct size and enhance post-ischemic functional recovery. Twenty-four anesthetized rabbits underwent 30 min. normothermic global ischemia with 120 min. reperfusion in a buffer-perfused isolated, paced heart model and divided into four groups. Global ischemic hearts (GI, n = 6) were subjected to 30 min. global ischemia without intervention. Control hearts (n=6) were subjected to perfusion without ischemia. Ischemic preconditioned hearts (IPC, n=6) were subjected to one cycle of 5 min. global ischemia and 5 min. reperfusion prior to global ischemia. IPC + Ado hearts (n=6) received IPC and adenosine administration (100 m mol/L) during 3 min. early reperfusion period. Post-ischemic functional recovery was better in IPC + Ado hearts as compared to GI and IPC hearts, but the effect of post-ischemic functional recovery in IPC + Ado hearts became weaker during 120 min. reperfusion after prolong ischemic insult. Infarct size wre 1.0 ± 0.3% in Control hearts, 32.9 ± 5.1% in GI hearts, 13.8 ± 1.3% in IPC hearts and 8.1 ± 0.9% in IPC + Ado hearts. Infarct size in IPC hearts was significantly decreased (p<0.01) as compared to GI hearts. The reduction rate against myocardial necrosis in IPC + Ado hearts versus GI hearts was higher as compared to IPC hearts versus GI hearts (p<0.001, IPC+Ado hearts vs GI hearts; p<0.01, IPC hearts vs GI hearts; p = ns, IPC + Ado hearts vs Control hearts). These data suggest that adenosine administration during the early reperfusion period reinforce IPC effect and reduce myocardial reperfusion injury. Cardiomyoprotective effects of IPC and exogenous adenosine are exerted during early reperfusion after coronary occlusion in the isolated perfused rabbit hearts.     

温血停搏液术终灌注对缺血再灌注心肌线粒体功能的影响

利用猫体外循环模型观察心肌缺血后温血停搏液再灌注对线粒体功能的影响。结果发现，心肌缺血６Ｏｍｉｎ时，线粒体功能呈现下降趋势，但与正常组相比，相差不显著。单纯再灌注组恢复正常血供６０ｍｉｎ后，线粒体功能进一步下降，同正常组或缺血组相比，相差非常显著。而温血停搏液再灌注可保护线粒体功能，同单纯再灌注组相比，两者相差显著表明心肌急性缺血后温血停搏液再灌注可减轻心肌线粒体再灌注损伤。     

Verapamil crystalloid cardioplegia: an experimental evaluation of dose-response relationships

Calcium channel blockers have been advocated as agents which enhance myocardial protection during ischemia and reperfusion. Unfortunately, while cellular integrity is preserved, myocardial function is depressed as a result of the negative inotropic effects of these agents. In order to assess the efficacy of verapamil cardioplegia, 25 isolated perfused rabbit hearts were studied. A model of normothermic ischemic arrest was utilized, employing either verapamil-free crystalloid cardioplegia or cardioplegia containing verapamil in concentrations of 0.5, 1.0, or 5.0 mg/liter. All three verapamil-treated groups demonstrated increased postischemic left ventricular developed pressure and improved postischemic compliance when compared with the untreated group (P less than 0.05). However, myocardial function was significantly depressed at 15 min of reperfusion in the 1.0 and 5.0 mg/liter verapamil-treated groups when compared with the 0.5 ml/liter group (P less than 0.05). These data suggest that the addition of verapamil to crystalloid cardioplegia results in enhanced myocardial function while minimizing the early reperfusion depression associated with higher dose therapy.