Dichotomy of ischemic preconditioning: improved postischemic contractile function despite intensification of ischemic contracture

BACKGROUND: Acceleration of ischemic contracture is conventionally accepted as a predictor of poor postischemic function. Hence, protective interventions such as cardioplegia delay ischemic contracture and improve postischemic contractile recovery. We compared the effect of ischemic preconditioning and cardioplegia (alone and in combination) on ischemic contracture and postischemic contractile recovery. METHODS AND RESULTS: Isolated rat hearts were aerobically perfused with blood for 20 minutes before being subjected to zero-flow normothermic global ischemia for 35 minutes and reperfusion for 40 minutes. Hearts were perfused at a constant pressure for 60 mm Hg and were paced at 360 beats per minute. Left ventricular developed pressure and ischemic contracture were assessed with an intraventricular balloon. Four groups (n=8 hearts per group) were studied: control hearts with 35 minutes of unprotected ischemia, hearts preconditioned with one cycle of 3 minutes of ischemia plus 3 minutes of reperfusion before 35 minutes of ischemia, hearts subjected to cardioplegia with St Thomas' solution infused for 1 minute before 35 minutes of ischemia, and hearts subjected to preconditioning plus cardioplegia before 35 minutes of ischemia. After 40 minutes of reperfusion, each intervention produced a similar improvement in postischemic left ventricular development pressure (expressed as a percentage of its preischemic value: preconditioning, 44 +/- 2%; cardioplegia, 53 +/- 3%; preconditioning plus cardioplegia, 54 +/- 4% and control, 26 +/- 6%, P<.05). However, preconditioning accelerated whereas cardioplegia delayed ischemic contracture; preconditioning plus cardioplegia gave an intermediate result. Thus, times to 75% contracture were as follows: control, 14.3 +/- 0.4 minutes; preconditioning, 6.2 +/- 0.3 minutes; cardioplegia 23.9 +/- 0.8 minutes; and preconditioning plus cardioplegia 15.4 +/- 2.4 minutes (P<.05 preconditioning and cardioplegia versus control). In additional experiments, using blood- and crystalloid-perfused hearts, we describe the relationship between the number of preconditioning cycles and ischemic contracture. CONCLUSIONS: Although preconditioning accelerates, cardioplegia delays, and preconditioning plus cardioplegia has little effect on ischemic contracture, each affords similar protection of postischemic contractile function. These results question the utility of ischemic contracture as a predictor of the protective efficacy of anti-ischemic interventions. They also suggest that preconditioning and cardioplegia may act through very different mechanisms.     

The effect of coenzyme Q10 and cold cristalloid cardioplegia on hypothermic global ischemia

Coenzyme Q10 (CoQ10, ubiquinone) has been shown to be protective against myocardial ischemia/reperfusion induced injury. The purpose of this study was to investigate the effect of CoQ10 added to cold cristalloid cardioplegia on hypothermic ischemia and normothermic reperfusion using an isolated working rat heart. Hearts (n = 6-9/group) from male Wistar rats were aerobically (37 degrees C) perfused (20 min) with bicarbonate buffer. This was followed by a 3-min infusion of St. Thomas' Hospital cardioplegic solution containing various concentrations of CoQ10 (0, 1, 3, 6, 12, and 58 mumol/L). Hearts were then subjected to 180 min of hypothermic (20 degrees C) global ischemia and 35 min of normothermic (37 degrees C) reperfusion (15 min Langendorff, 20 min working). Ventricular fibrillation (Vf) upon reperfusion was irreversible in the 12 and 58 mumol/ L CoQ10 groups (4/6 and 3/6, respectively). In the hearts which Vf upon reperfusion was not irreversible, the percent recovery of aortic flow (%AF) was 43.3 +/- 5.4% (n = 9) in the control group versus 31.6 +/- 7.7% (n = 6), 38.0 +/- 12.0% (n = 6), 27.2 +/- 6.9% (n = 6), 31.3% (n = 2), and 30.4 +/- 14.2% (n = 3) in the 1, 3, 6, 12, and 58 mumol/L CoQ10 groups, respectively. Creatine kinase leakage during Langendorff reperfusion tended to be greater in the 12 and 58 mumol/L CoQ10 groups than in the control group. Thus, CoQ10 in the cold cristalloid cardioplegic solution induced irreversible Vf upon reperfusion and failed to improve functional recoveries following hypothermic global ischemia.     

The ultrastructure of chicken gizzard vinculin as visualized by high-resolution electron microscopy

OBJECTIVES: A myocardial calcium-independent PLA2 has been described that is activated during myocardial ischemia and this enzyme may modulate ATP-sensitive potassium channels (KATP). The aim of this study was to determine the effect of an inhibitor of this enzyme, a bromoenol lactone, in isolated globally ischemic rat hearts. METHODS: Isolated rat hearts were treated for 10 min with 0.3-6 microM bromoenol lactone and then subjected to 25 min ischemia and 30 min reperfusion. RESULTS: The bromoenol lactone significantly increased coronary flow in nonischemic myocardium, and slightly reduced cardiac function at 6 microM. During global ischemia, time to contracture was significantly increased from vehicle group values in the presence of the bromoenol lactone (EC50 = 1.2 microM). During reperfusion, a concentration-dependent increase in function and a reduction in LDH release were observed for the PLA2 inhibitor. The concentrations of the PLA2 inhibitor which were significantly cardioprotective, inhibited this enzyme in membrane fractions of rat myocardium (IC50 = 0.87 microM). The KATP blocker sodium 5-hydroxydecanoate (5-HD) inhibited the increase in time to contracture observed for the bromoenol lactone. During reperfusion, 5-HD abolished the protective effects of the bromoenol lactone on cardiac function and LDH release. Glyburide had similar effects on the cardioprotective activity of the bromoenol lactone, although it only partially abolished the LDH reducing effect of this agent. CONCLUSIONS: The bromoenol lactone protects ischemic myocardium at concentrations which also inhibit calcium-independent PLA2. This cardioprotection can be attenuated by blockers of KATP, suggesting a potential mechanism for modulation of myocardial KATP.     

Temporal relation of ATP-sensitive potassium-channel activation and contractility before cardioplegia

BACKGROUND: Pharmacologic treatment using potassium-channel openers (PCOs) before cardioplegic arrest has been demonstrated to provide beneficial effects on left ventricular performance with subsequent reperfusion and rewarming. However, the PCO treatment interval necessary to provide protective effects during cardioplegic arrest remains to be defined. The present study was designed to determine the optimum period of PCO treatment that would impart beneficial effects on left ventricular myocyte contractility after simulated cardioplegic arrest. METHODS: Left ventricular porcine myocytes were assigned randomly to three groups: (1) normothermic control = 37 degrees C for 2 hours; (2) cardioplegia = K+ (24 mEq/L) at 4 degrees C for 2 hours followed by reperfusion and rewarming; and (3) PCO and cardioplegia = 1 to 15 minutes of treatment with the PCO aprikalim (100 micromol/L) at 37 degrees C followed by hypothermic (4 degrees C) cardioplegic arrest and subsequent rewarming. Myocyte contractility was measured after rewarming by videomicroscopy. A minimum of 50 myocytes were examined at each treatment and time point. RESULTS: Myocyte velocity of shortening was reduced after cardioplegic arrest and rewarming compared with normothermic controls (63+/-3 microm/s versus 32+/-2 microm/s, respectively; p < 0.05). With 3 minutes of PCO treatment, myocyte velocity of shortening was improved after cardioplegic arrest to values similar to those of normothermic controls (56+/-3 microm/s). Potassium channel opener treatment for less than 3 minutes did not impart a protective effect, and the protective effect was not improved further with more prolonged periods of PCO treatment. CONCLUSIONS: A brief interval of PCO treatment produced beneficial effects on left ventricular myocyte contractile function in a simulated model of cardioplegic arrest and rewarming. These results suggest that a brief period of PCO treatment may provide a strategy for myocardial protection during prolonged cardioplegic arrest in the setting of cardiac operation.     

Enflurane and isoflurane, but not halothane, protect against myocardial reperfusion injury after cardioplegic arrest with HTK solution in the isolated rat heart

To investigate the effects of halothane, enflurane, and isoflurane on myocardial reperfusion injury after ischemic protection by cardioplegic arrest, isolated perfused rat hearts were arrested by infusion of cold HTK cardioplegic solution containing 0.015 mmol/L Ca2+ and underwent 30 min of ischemia and a subsequent 60 min of reperfusion. Left ventricular (LV) developed pressure and creatine kinase (CK) release were measured as variables of myocardial function and cellular injury, respectively. In the treatment groups (each n = 9), anesthetics were given during the first 30 min of reperfusion in a concentration equivalent to 1.5 minimum alveolar anesthetic concentration of the rat. Nine hearts underwent the protocol without anesthetics (controls). Seven hearts underwent ischemia and reperfusion without cardioplegia and anesthetics. In a second series of experiments, halothane was tested after cardioplegic arrest with a modified HTK solution containing 0.15 mmol/L Ca2+ to investigate the influence of calcium content on protective actions against reperfusion injury by halothane. LV developed pressure recovered to 59%+/-5% of baseline in controls. In the experiments with HTK solution, isoflurane and enflurane further improved functional recovery to 84% of baseline (P < 0.05), whereas halothane-treated hearts showed a functional recovery similar to that of controls. CK release was significantly reduced during early reperfusion by isoflurane and enflurane, but not by halothane. After cardioplegic arrest with the Ca2+-adjusted HTK solution, halothane significantly reduced CK release but did not further improve myocardial function. Isoflurane and enflurane given during the early reperfusion period after ischemic protection by cardioplegia offer additional protection against myocardial reperfusion injury. The protective actions of halothane depended on the calcium content of the cardioplegic solution. IMPLICATIONS: Enflurane and isoflurane administered in concentrations equivalent to 1.5 minimum alveolar anesthetic concentration in rats during early reperfusion offer additional protection against myocardial reperfusion injury even after prior cardioplegic protection. Protective effects of halothane solely against cellular injury were observed only when cardioplegia contained a higher calcium concentration.     

Adenosine-enhanced ischemic preconditioning provides enhanced postischemic recovery and limitation of infarct size in the rabbit heart

OBJECTIVE: The purpose of this study was to determine the effect of an intracoronary bolus injection of adenosine used in concert with ischemic preconditioning on postischemic functional recovery and infarct size reduction in the rabbit heart and to compare adenosine-enhanced ischemic preconditioning with ischemic preconditioning and magnesium-supplemented potassium cardioplegia. METHODS: New Zealand White rabbits (n = 36) were used for Langendorff perfusion. Control hearts were perfused at 37 degrees C for 180 minutes; global ischemic hearts received 30 minutes of global ischemia and 120 minutes of reperfusion; magnesium-supplemented potassium cardioplegic hearts received cardioplegia 5 minutes before global ischemia; ischemic preconditioned hearts received 5 minutes of zero-flow global ischemia and 5 minutes of reperfusion before global ischemia; adenosine-enhanced ischemic preconditioned hearts received a bolus injection of adenosine just before the preconditioning. To separate the effects of adenosine from adenosine-enhanced ischemic preconditioning, a control group received a bolus injection of adenosine 10 minutes before global ischemia. RESULTS: Infarct volume in global ischemic hearts was 32.9% +/- 5.1% and 1.03% +/- 0.3% in control hearts. The infarct volume decreased (10.23% +/- 2.6% and 7.0% +/- 1.6%, respectively; p < 0.001 versus global ischemia) in the ischemic preconditioned group and control group, but this did not enhance postischemic functional recovery. Magnesium-supplemented potassium cardioplegia and adenosine-enhanced ischemic preconditioning significantly decreased infarct volume (2.9% +/- 0.8% and 2.8% +/- 0.55%, respectively; p < 0.001 versus global ischemia, p = 0.02 versus ischemic preconditioning and p = 0.05 versus control group) and significantly enhanced postischemic functional recovery. CONCLUSIONS: Adenosine-enhanced ischemic preconditioning is superior to ischemic preconditioning and provides equal protection to that afforded by magnesium-supplemented potassium cardioplegia.     

Transgenic A1 adenosine receptor overexpression markedly improves myocardial energy state during ischemia-reperfusion

A1 adenosine (A1AR) activation may reduce ischemia-reperfusion injury. Metabolic and functional responses to 30 min global normothermic ischemia and 20 min reperfusion were compared in wild-type and transgenic mouse hearts with approximately 100-fold overexpression of coupled cardiac A1ARs. 31P-NMR spectroscopy revealed that ATP was better preserved in transgenic v wild-type hearts: 53 +/- 11% of preischemic ATP remained after ischemia in transgenic hearts v only 4 +/- 4% in wild-type hearts. However, recovery of ATP after reperfusion was similar in transgenic (46 +/- 5%) and wild-type hearts (37 +/- 12%). Reductions in phosphocreatine (PCr) and cytosolic pH during ischemia were similar in both groups. However, recovery of PCR on reperfusion was higher in transgenic (67 +/- 8%) v wild-type hearts (36 +/- 8%), and recovery of pH was greater in transgenic (pH = 7.11 +/- 0.05) v wild-type hearts (pH = 6.90 +/- 0.02). Bioenergetic state ([ATP]/[ADP].[Pi]) was higher in transgenic v wild-type hearts during ischemia-reperfusion. Time to ischemic contracture was prolonged in transgenic (13.6 +/- 0.8 min) v wild-type hearts (10.4 +/- 0.3 min). Degree of contracture was lower and recovery of function in reperfusion higher in transgenic v wild-type hearts. In conclusion, A1AR overexpression reduces ATP loss and improves bioenergetic state during severe ischemic insult and reperfusion. These changes may contribute to improved functional tolerance.     

Cerebellar granule cell GABA(A) receptors studied at the single-channel level: modulation by protein kinase G

BACKGROUND: This study was designed to evaluate the adenosine-triphosphate-sensitive potassium channel opener pinacidil as a blood cardioplegic agent. METHODS: Using a blood-perfused, parabiotic, Langendorff rabbit model, hearts underwent 30 minutes of normothermic ischemia protected with blood cardioplegia (St. Thomas' solution [n = 8] or Krebs-Henseleit solution with pinacidil [50 micromol/L, n = 81) and 30 minutes of reperfusion. Percent recovery of developed pressure, mechanical arrest, electrical arrest, reperfusion ventricular fibrillation, percent tissue water, and myocardial oxygen consumption were compared. RESULTS: The percent recovery of developed pressure was not different between the groups (52.3 +/- 5.9 and 52.8 +/- 6.9 for hyperkalemic and pinacidil cardioplegia, respectively). Pinacidil cardioplegia was associated with prolonged electrical and mechanical activity (14.4 +/- 8.7 and 6.1 +/- 3.9 minutes), compared with hyperkalemic cardioplegia (1.1 +/- 0.6 and 1.1 +/- 0.6 minutes, respectively; p < 0.05). Pinacidil cardioplegia was associated with a higher reperfusion myocardial oxygen consumption (0.6 +/- 0.1 versus 0.2 +/- 0.0 mL/100 g myocardium/beat; p < 0.05) and a higher percent of tissue water (79.6% +/- 0.7% versus 78.6% +/- 1.2%; p < 0.05). CONCLUSIONS: Systolic recovery was not different between groups, demonstrating comparable effectiveness of pinacidil and hyperkalemic warm blood cardioplegia.     

The superiority of pinacidil over adenosine cardioplegia in blood-perfused isolated hearts

BACKGROUND: Our laboratory has shown that the potassium-channel opener pinacidil is an effective cardioplegic agent. A theoretical benefit of cardioplegia with potassium-channel openers is that it arrests the heart at hyperpolarized membrane potentials, a state of minimal metabolic requirement. This study was designed to examine another nondepolarizing agent, adenosine, and to test the hypothesis that it could provide comparable cardioprotection or augment potassium-channel opener cardioplegia. METHODS: Using the blood-perfused Langendorff technique, isolated rabbit hearts were arrested for 30 minutes of global normothermic ischemia. Cardioplegia consisted of either Krebs-Henseleit solution alone (control) or with pinacidil (50 micromol/L), adenosine (200 micromol/L to 1 mmol/ L), or pinacidil + adenosine (200 micromol/L). Recovery of developed pressure and coronary flow were recorded. RESULTS: Postischemic functional recovery for control, pinacidil, adenosine, and adenosine + pinacidil groups was 44.1%+/-3.4%, 59.5%+/-5.2% (p < 0.05 versus control), 37.0%+/-4.5%, and 56.0%+/-2.9%, respectively. CONCLUSIONS: Adenosine, alone or as adjunct to pinacidil cardioplegia, was not an effective cardioplegic agent, despite shorter times to electromechanical arrest than control. The ineffectiveness of adenosine suggests that the cardioprotective properties of potassium-channel openers involve mechanisms other than the avoidance of membrane depolarization.     

Coronary vascular regulation during postcardioplegia reperfusion

BACKGROUND: This study extends previous investigations of global and regional myocardial blood flow during early postcardioplegia reperfusion. The hypothesis tested is that coronary vascular regulation becomes abnormal within 3 minutes after the start of postcardioplegia reperfusion. METHODS: Pigs (n = 40) were supported by cardiopulmonary bypass and 38 degrees C blood cardioplegic solution was infused. A control preischemic microsphere injection (No. 1) was given in asystolic hearts. Groups 1 to 3 had 1 hour of hypothermic cardioplegic arrest. Group 4 (control group) had 1 hour of perfusion without cardioplegia. A blood cardioplegic solution at 38 degrees C and 70 mm Hg pressure was infused to maintain asystole during the initial 7 to 10 minutes of reperfusion in all groups. Left ventricular intracavitary pressures were set at 0, 10, 20, or 0 mm Hg in groups 1, 2, 3, and 4 (n = 10 pigs per group), respectively, during the initial 7 minutes of reperfusion. The ventricle was then decompressed. At 30 seconds, 3 minutes, and 6 minutes after reperfusion, microsphere injections 2, 3, and 4 were given in asystolic hearts. Microsphere injection No. 5 was given 10 minutes after reperfusion in beating vented hearts. RESULTS: (1) Left ventricular distention during the initial 7 minutes of reperfusion after hypothermic cardioplegic arrest attenuates postischemic hyperemia. (2) Left ventricular intracavitary pressure of 20 mm Hg during reperfusion causes a decrease in endocardial blood flow relative to epicardial blood flow at 6 minutes after reperfusion. (3) Global myocardial blood flow during postcardioplegia reperfusion falls significantly below preischemic control values despite the return of electromechanical activity. INFERENCE: Coronary vascular regulation (i.e., coronary resistance and metabolic flow recruitment) becomes abnormal within 3 minutes after the start of reperfusion after hypothermic blood cardioplegic arrest.     

Ischemic preconditioning prior to myocardial protection with cold blood cardioplegia in coronary surgery

OBJECTIVE: Encouraging results on myocardial preconditioning in experimental models of infarction, stunning or prolonged ischemia raise the question whether preconditioning techniques may enhance conventional cardioplegic protection used for routine coronary surgery. METHODS: A prospective clinical trial was conducted to investigate the effect of additional ischemic normothermic preconditioning prior to cardioplegic arrest applying cold blood cardioplegia in patients scheduled for routine coronary surgery (3 vessel disease, left ventricular ejection fraction > 50%). Two cross clamp periods of 5 min with the hearts beating in sinus rhythm were applied followed by 10 min of reperfusion, each (n = 7, group I). Inducing moderate hypothermia cold blood cardioplegia was delivered antegradely. In control groups, cold intermittent blood cardioplegia (n = 7, group II) was used alone. Coronary sinus effluents were analyzed for release of creatine kinase (CK), CK-MB, lactate, and troponin T at 1, 3, 6, 9, and 12 h. In addition, postoperative catecholamine requirements were monitored. RESULTS: The procedure was tolerated well, and no perioperative myocardial infarction in any of the groups studied occurred. Concentrations of lactate tended to be higher in group I, but this difference was not significant. In addition, no significant differences for concentrations of CK, CK-MB, and troponin T were found. Following ischemic preconditioning an increased dosage of dopamine was required within the first 12 h postoperatively (group I: 2.63 +/- 1.44 microg/kg/min, group II: 0.89 +/- 1.06 microg/kg/min). CONCLUSIONS: Combining ischemic preconditioning and cardioplegic protection with cold blood cardioplegia does not appear to ameliorate myocardial protection when compared to cardioplegic protection applying cold blood cardioplegia alone. Inversely, contractile function seemed to be impaired when applying this protocol of ischemic preconditioning.     

Effect of pinacidil on rat hearts undergoing hypothermic cardioplegia

We studied the effect of pinacidil, a potassium-channel opener, on the hemodynamic, biochemical, and ultrastructural changes in rat hearts undergoing hypothermic cardioplegia. Fifty-four male Wistar rats weighing 250 to 300 g were used. Isolated hearts were prepared for modified Langendorff circulation in the working mode using modified Krebs-Henseleit bicarbonate solution bubbled with a 95% O2 and 5% CO2 gas mixture. Eighty minutes of cardioplegia at 25 degrees C was followed by normothermic reperfusion for 30 minutes. Pinacidil, 5, 10, or 50 mumol/L added to the cardioplegic solution, did not affect heart rate, but is significantly improved the recovery of aortic flow as compared with controls (88.1% +/- 4.3 [5 mumol/L]; 83.2% +/- 8.5% [10 mumol/L]; 90.3% +/- 5.3% [50 mumol/L] compared with 55.6 +/- 4.3% [control]; p < 0.05). Administration of pinacidil during reperfusion did not further enhance the recovery of aortic flow. The dose-response curve of aortic flow to the pinacidil concentrations was flat from 5 to 50 mumol/L. However, preservation of myocardial adenosine triphosphate and calcium concentrations and mitochondrial morphology suggested that the optimal concentration of pinacidil cardioplegia is 10 mumol/L.     

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

BACKGROUND: Recently we have reported a novel myo-protective 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.     

Virtual colonoscopy: imaging features with colonoscopic correlation

BACKGROUND: We determined whether activation of the nitric oxide/cyclic guanosine monophosphate pathway by sodium nitroprusside (SNP) protects hearts subjected to cardioplegic arrest and prolonged hypothermic storage. METHODS: Isolated rat hearts arrested with St. Thomas' II cardioplegia and stored at 3 degrees +/- 1 degree C for 8 hours were reperfused at 37 degrees C in Langendorff (10 minutes) and working (60 minutes) modes. RESULTS: During reperfusion, left ventricular work was depressed in stored hearts relative to fresh hearts. When present during arrest, storage, and both reperfusion phases, SNP (200 mumol/L) improved work to values close to those in fresh hearts. When added only during the 10-minute period of Langendorff reperfusion, SNP also improved the subsequent recovery of work. This effect was antagonized by the soluble guanylyl cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ). Poststorage coronary perfusion was not increased by SNP. CONCLUSIONS: The ability of SNP to enhance recovery independent of changes in coronary perfusion and in an ODQ-sensitive manner suggests that SNP-induced protection is due to activation of the myocardial nitric oxide/cyclic guanisine monophosphate pathway. These results suggest that supplementing cardioplegic solutions with SNP, administering SNP during early reperfusion, or both may offer additional means to improve donor heart preservation.     

Influence of preconditioning on rat heart subjected to prolonged cardioplegic arrest

BACKGROUND: Ischemic preconditioning (IP) can reduce lethal injury to the myocardium induced by prolonged ischemia. However, little is known about the effect of preconditioning on the heart subjected to cardioplegic arrest and hypothermic preservation. We evaluated the effect of IP on myocardial metabolism, mechanical performance, and coronary endothelial function after cardioplegic arrest and prolonged hypothermic preservation. METHODS: An isovolumic Langendorff perfused rat heart model was used, and hearts were divided into two groups. The first group (IP, n = 14) was preconditioned by 5 minutes of global normothermic (37 degrees C) ischemia followed by 10 minutes of normothermic reperfusion before 6 hours of cold (4 degrees C) preservation, followed by 60 minutes of reperfusion. The second group (control, n = 15) was subjected to 6 hours of cold preservation followed by 60 minutes of reperfusion without preconditioning. Mechanical function was assessed using left ventricular balloon by constructing pressure-volume curves in two ways: at defined left ventricular volumes or at defined left ventricular end-diastolic pressures. Initially, the volume of the balloon was increased incrementally from 0 to 150 microL in 25-microL steps. Measurements were then repeated with loading balloon to achieve left ventricular end-diastolic pressure of 5, 10, 15, or 20 mm Hg. Myocardial function was assessed before ischemia and at 15 or 60 minutes of reperfusion. Metabolic status of the heart was evaluated by measuring the release of purine catabolites during the initial 15 minutes of reperfusion and concentrations of myocardial nucleotides at the end of reperfusion. Endothelium-mediated vasodilatation was evaluated using 10 mumol/L 5-hydroxytryptamine before and after ischemia. RESULTS: Left ventricular end-diastolic pressure values were significantly lower in the IP group, by 20% to 40%, during the reperfusion phase at each volume of the balloon compared with the control group. The rate-pressure product was more favorable during reperfusion in the IP than in the control group because of a 15% increased heart rate in the IP group. The release of purine catabolites from the heart during the reperfusion phase was reduced (p < 0.01) in the IP group (0.66 +/- 0.04 mumol) relative to the control group (0.92 +/- 0.06 mumol). No difference in the recovery of systolic function, myocardial adenosine triphosphate concentration, or endothelial function was observed between the groups. CONCLUSIONS: Under conditions of cardioplegic arrest and hypothermic preservation, IP can offer additional protection for the heart by preventing an increase in diastolic stiffness. However, metabolic improvement or better preservation of the systolic or endothelial function was not observed in this model.     

Resistance of the failing dystrophic hamster heart to the cardioprotective effects of diltiazem and clentiazem: evidence of coronary vascular dysfunctions

Although hypothermia and cardioplegic cardiac arrest provide effective protection during cardiac surgery, ischemia of long duration, poor preoperative myocardial function, and ventricular hypertrophy may lead to heterogeneous delivery of cardioplegic solutions, incomplete protection, and impaired postischemic recovery. Calcium antagonists are potent cardioprotective agents, but their efficacy in the presence of cold cardioplegia is still controversial, especially in heart failure, since it is often believed that failing hearts are more sensitive to their negative inotropic and chronotropic actions. However, recent data have demonstrated that the benzothiazepine-like calcium antagonists diltiazem and clentiazem, in selected dose ranges, elicit significant cardioprotection independently of intrinsic cardiodepression, thus lending support to their use in cardioprotective maneuvers involving the failing heart. We therefore evaluated the cardioprotective interaction of diltiazem, clentiazem, and cold cardioplegia in both normal and failing ischemic hearts. Hearts were excised from 200- to 225-day-old cardiomyopathic hamsters (CMHs) of the UM-X7.1 line and age-matched normal healthy controls. Ex vivo perfusion was performed at a constant pressure (140 cmH2O; 1 cmH2O = 98.1 Pa) according to the method of Langendorff. Heart rate, left ventricular developed pressure (LVDP), and coronary flow were monitored throughout the study. Global ischemia was produced for 90 min by shutting down the perfusate flow, followed by reperfusion for 30 min. Normal and failing CMH hearts were either untreated (control) or perfused at the onset of global ischemia with one of the following combinations: cold cardioplegia alone (St. Thomas' Hospital cardioplegic solution, 4 degrees C, infused for 2 min), cold cardioplegia + 10 nM diltiazem, or cold cardioplegia + 10 nM clentiazem. The cardiac and coronary dilator properties of 10 nM diltiazem and 10 nM clentiazem alone were investigated in separate groups of isolated preparations. Failing CMH hearts had lower basal LVDP (42 +/- 2 vs. 77 +/- 2 mmHg (1 mmHg = 133.3 Pa) for normal hearts, p < 0.05), while coronary flow was only slightly reduced (5.6 +/- 0.2 vs. 6.2 +/- 0.2 mL/min for normal hearts). Following 90 min global ischemia, coronary flow was increased in both groups, but the peak hyperemic response declined only in failing CMH hearts (+50 +/- 17 vs. +82 +/- 17% in normal hearts). In normal hearts, LVDP virtually recovered within 5 min of reperfusion but steadily decreased thereafter (-37 +/- 4% at 30 min). In contrast, in failing CMH hearts, LVDP significantly decreased early during reperfusion but improved over time (-19 +/- 7% at 30 min). In normal hearts, the addition of diltiazem or clentiazem to cold cardioplegic solutions resulted in improved postischemic contractile function for the duration of reperfusion (85 +/- 4% vs. only 71 +/- 6% for cardioplegia, p < 0.05). The post-ischemic increase in coronary flow was similar in all groups. In failing CMH hearts, the addition of diltiazem or clentiazem afforded no significant contractile benefit at reperfusion. In nonischemic normal hearts, infusion of diltiazem or clentiazem (10 nM) alone increased coronary flow (+6 +/- 1% for diltiazem and +24 +/- 3% for clentiazem) without significant negative inotropic or chronotropic effects. In nonischemic failing CMH hearts, infusion of diltiazem or clentiazem did not elicit cardiodepression. In contrast their coronary dilator actions reverted to vasoconstriction (diltiazem) or were significantly attenuated (clentiazem). From these experiments we can conclude that, compared with the normal heart, the failing CMH heart adapted differently to global ischemia.     

Dichloroacetate enhanced myocardial functional recovery post-ischemia : ATP and NADH recovery

This study was undertaken to determine the effect of dichloroacetate (DCA) on myocardial functional and metabolic recovery following global ischemia. Isolated rabbit hearts were subjected to 120 min of mildly hypothermic (34 degrees C), cardioplegic arrest with multidose, modified St. Thomas' cardioplegia. Hearts were reperfused with either physiologic salt solution (PSS) as controls, (CON, n = 10) or PSS containing DCA (DCA, n = 6) at a concentration of 1 mM. Functional and metabolic indices were determined at baseline and at 15, 30, and 45 min of reperfusion. In four DCA and four CON hearts, myocardial biopsies were taken at baseline, end-ischemia, 15 and 45 min for nucleotide levels. Functional recovery was significantly better in hearts reperfused with DCA as demonstrated by recovery of baseline developed pressure (DCA = 69 +/- 5%, CON = 45 +/- 9%) and dP/dt (DCA = 64% +/- 10% versus CON = 48% +/- 10%). Coronary blood flow was not different between groups either at baseline or during reperfusion, but myocardial oxygen consumption (MVO2) was increased in the DCA versus CON hearts (79% +/- 20% of baseline vs 50% +/- 18%). Recovery of myocardial adenylate energy status was improved in the DCA versus CON hearts (ATP recovered to 45% +/- 20% versus 8% +/- 6% of baseline). Coronary sinus lactate concentration was decreased in DCA perfused hearts at 45 min of reperfusion. Percent of baseline NADH values was similar at 15 min of reperfusion, but at 45 min, DCA hearts showed a decrease in NADH levels, while CON hearts showed an increase (DCA = 48%; CON = 121%). The enhanced myocardial function and improved metabolic status noted with DCA may result from increased oxidative phosphorylation due to altered pyruvate dehydrogenase (PDH) activity.     

Nicorandil augments regional ischemia-induced monophasic action potential shortening and potassium accumulation without serious proarrhythmia

Nicorandil is a clinically used nitrovasodilator that has a property as an opener of ATP-sensitive potassium (KATP) channels in vitro. We examined whether nicorandil at a clinically used dose augmented regional ischemia-induced monophasic action potential (MAP) shortening and increase in extracellular potassium concentration ([K+]o), and how it affected arrhythmia occurrence. Five-minute occlusion of a distal site of the left anterior descending coronary artery (LAD) was repeated at 30-min intervals in anesthetized open-chest dogs while recording MAP or measuring [K+]o with a potassium-sensitive valinomycin electrode from the epicardial center of the ischemic myocardium. Nicorandil (0.2-0.5 mg/kg) was administered intravenously (i.v.) 5 min before the third occlusion, and the data were compared with those during the second occlusion (control). During the second occlusion, MAP duration at 90% repolarization (APD90) shortened (mean rate for 5 min, 13 +/- 3%, n = 11) and [K+]o increased from 3.7 +/- 0.1 to 6.2 +/- 0.8 mM at 5 min (n = 12). These changes were reversed < or = 3 min after reperfusion. Before the third occlusion, baseline APD90 and [K+]o were not altered by nicorandil; however, the extent of occlusion-induced shortening of APD90 (25 +/- 4%) and [K+]o increase (7.8 +/- 1.6 mM) was augmented by the pretreatment. The drug effect was attenuated by a concomitant pretreatment with 5-hydroxydecanoate, a specific blocker of KATP channels (n = 2). The prevalence of ventricular fibrillation (VF) during occlusion/reperfusion sequence was reduced after nicorandil (1 of 25 vs. 5 of 25) without de novo VF. These results suggest that nicorandil at a clinical dose facilitates regional ischemia-induced activation of myocardial KATP channels without causing serious proarrhythmia. Such a property might help protect the myocardium against ischemia/reperfusion damage.     

Mitochondrial ATP-dependent potassium channels: novel effectors of cardioprotection?

BACKGROUND: Brief interruptions of coronary blood flow paradoxically protect the heart from subsequent prolonged ischemia. The basis of such endogenous cardioprotection, known as "ischemic preconditioning," remains uncertain. Pharmacological evidence has implicated ATP-dependent potassium (KATP) channels in the mechanism of preconditioning; however, the effects of sarcolemmal KATP channels on excitability cannot account for the protection. METHODS AND RESULTS: We simultaneously measured flavoprotein fluorescence, an index of mitochondrial redox state, and sarcolemmal KATP currents in intact rabbit ventricular myocytes. Our results show that diazoxide, a KATP channel opener, selectively activates mitochondrial KATP channels. Diazoxide induced reversible oxidation of flavoproteins with an EC50 of 27 micromol/L but did not activate sarcolemmal KATP channels. The subcellular site of diazoxide action is further localized to mitochondria by confocal imaging of fluorescence arising from flavoproteins and tetramethylrhodamine ethyl ester. In a cellular model of simulated ischemia, inclusion of diazoxide decreased the rate of cell death to about half of that in controls. Both the redox changes and protection are inhibited by the KATP channel blocker 5-hydroxydecanoic acid. CONCLUSIONS: Our results demonstrate that diazoxide targets mitochondrial but not sarcolemmal KATP channels and imply that mitochondrial KATP channels may mediate the protection from KATP channel openers.     

Antimicrobial activity in the skin of the channel catfish Ictalurus punctatus: characterization of broad-spectrum histone-like antimicrobial proteins

BACKGROUND: A major reduction in the energy demand of the myocardium results from the electromechanical arrest, and cooling contributes to a lesser degree to this reduction. It is from this assumption that strategies of myocardial protection, utilizing warm blood cardioplegic induction, followed by cold cardioplegia with terminal warm reperfusion before removal of the aortic cross clamp, became established as optimal myocardial protection. Continuous normothermic perfusion 'closed the loop' by avoiding myocardial ischemia and linking warm induction and terminal reperfusion. A series of laboratory and clinical data confirmed the benefits of warm heart surgery on myocardial function and metabolism. The disadvantages of continuous warm blood cardioplegia including disturbance of the operative field, led surgeons to administer warm hyperkalaemic blood intermittently as a new cardioplegic strategy. METHODS: This review examines the laboratory and clinical data with reference to the intermittent warm blood cardioplegia, to establish its experimental basis and place in clinical practice. CONCLUSIONS: Experimental observation and clinical application have established intermittent warm blood cardioplegia as a practical, effective and cheap myocardial protection technique, particularly with reference to coronary artery surgery.