Ischemic preconditioning enhances donor heart preservation

Myocardial Preconditioning: Characteristics, Mechanisms, and Clinical Applications

Perioperative myocardial ischemia and dysfunction re main prevalent after cardiac surgery despite the use of conventional measures to provide myocardial protec tion. Myocardial preconditioning is a powerful, endog enously regulated means of myocardial protection that may also have some clinical usage for patients undergo ing cardiac surgical procedures. The paradoxical con cept of using ischemia as a stimulus for myocardial protection has been studied extensively in animals and humans. The specific characteristics and constituents of preconditioning have been well identified. The mecha nism remains to be completely elucidated due to differ ences among species and experimental models. Some pharmacologic agents are capable of mimicking the classic mechanism of ischemic preconditioning. Pharma cologic and ischemic preconditioning may have signifi cant clinical use and therapeutic efficacy as a means of providing myocardial protection during cardiac surgery, especially in procedures that do not use cardioplegia and cardiopulmonary bypass, such as minimally inva sive coronary artery bypass grafting. This article re views the characteristics, mechanisms, potential clini cal applications, and therapeutic efficacy of myocardial preconditioning.

Hypothermic continuous machine perfusion enables preservation of energy charge and functional recovery of heart grafts in an ex vivo model of donation following circulatory death

OBJECTIVES

Cardiac transplantation using hearts from donors after circulatory death (DCD) is critically limited by the unavoidable warm ischaemia and its related unpredictable graft function. Inasmuch as hypothermic machine perfusion (MP) has been shown to improve heart preservation, we hypothesized that MP could enable the use of DCD hearts for transplantation.

METHODS

We recovered 16 pig hearts following anoxia-induced cardiac arrest and cardioplegia. Grafts were randomly assigned to two different groups of 4-h preservation using either static cold storage (CS) or MP (Modified LifePort© System, Organ Recovery Systems©, Itasca, Il). After preservation, the grafts were reperfused ex vivo using the Langendorff method for 60 min. Energetic charge was quantified at baseline, post-preservation and post-reperfusion by measuring lactate and high-energy phosphate levels. Left ventricular contractility parameters were assessed both in vivo prior to ischaemia and ex vivo during reperfusion.

RESULTS

Following preservation, the hearts that were preserved using CS exhibited higher lactate levels (57.1 ± 23.7 vs 21.4 ± 12.2 µmol/g; P < 0.001), increased adenosine monophosphate/adenosine triphosphate ratio (0.53 ± 0.25 vs 0.11 ± 0.11; P < 0.001) and lower phosphocreatine/creatine ratio (9.7 ± 5.3 vs 25.2 ± 11; P < 0.001) in comparison with the MP hearts. Coronary flow was similar in both groups during reperfusion (107 ± 9 vs 125 ± 9 ml/100 g/min heart; P = ns). Contractility decreased in the CS group, yet remained well preserved in the MP group.

CONCLUSION

MP preservation of DCD hearts results in improved preservation of the energy and improved functional recovery of heart grafts compared with CS.

Protective effect of ischemic preconditioning on the jejunal graft mucosa injury during cold preservation

Protection of intestinal graft mucosa during cold preservation is still an unmet need in clinical practice, thus affecting the success of transplantation. The present study investigates the ability of two ischemic preconditioning (IPC) procedures to limit cold preservation injury. Three groups of Sprague-Dawley rats were recruited (n=11 each) as follows: the short IPC (SIPC) performed through 4 cycles of mesenteric ischemia of 4 min each followed by 10 min of reperfusion, the long IPC (LIPC) obtained by 2 ischemic cycles of 12 min each followed by 10 min of reperfusion, and the control group (C) without IPC. Grafts were then stored in cold histidine-tryptophan-ketoglutarate solution and samples were taken at 0, 3, 6 and 9 h lasting preservation. Both IPC groups showed an advanced degree of preservation with delayed development of graft mucosa damage, mainly in the crypt region. At the beginning of preservation, the graft mucosa in both IPC groups showed lower degree of mucosal injury index (MII) by 50% in comparison with C group. Specifically, a significant improvement of MII was observed after 3h of preservation in the LIPC group (p<0.05) in comparison with untreated C grafts. Significant atrophy of the intestinal mucosa in C group was found after 3h of preservation (p<0.01), in SIPC group the progress of atrophy was delayed to 6 h (p<0.001), and in LIPC group only moderate decrease in that was found. A parallel increase of laminin expression with the MII rate after 6 and 9h of preservation in comparison with the level at time 0 was observed in all grafts (p<0.001 and p<0.01, respectively). In both IPC groups the apoptotic cell (AC) rate was significantly reduced at the beginning of cold preservation (p<0.05 both). Moreover, in both the SIPC and C groups, the progressive increase in MII rate connected with AC rate decrease was due to a predominance of necrosis. By contrast in the LIPC group, after an increase of nearly 50% in the AC rate at the 3rd hour, its level remained fairly constant during the further 6 h of preservation, thus probably preventing necrosis and improving graft viability.

Preservation of the donor heart: from basic science to clinical studies

The methods of donor heart preservation are aimed at minimizing graft dysfunction caused by ischaemia-reperfusion injury (IRI) which inevitably occurs during the ex vivo transport interval. At present, the standard technique of heart preservation is cardiac arrest followed by static cold storage in a crystalloid heart preservation solution (HPS). This technique ensures an acceptable level of heart protection against IRI for <6 h. In clinical trials, comparable levels of myocardial protection against IRI were provided by various HPSs. The growing shortage of donor hearts is one of the major factors stimulating the development of new techniques of heart preservation. Here, we summarize new HPS formulations and provide a focus for optimization of the composition of existing HPSs. Such methods of donor heart preservation as machine perfusion, preservation at sub-zero temperature and oxygen persufflation are also discussed. Furthermore, we review experimental data showing that pre- and post-conditioning of the cardiac graft can improve its function when used in combination with cold storage. The evidence on the feasibility of cardiac donation after circulatory death, as well as the techniques of heart reconditioning after a period of warm ischaemia, is presented. The implementation of new techniques of donor heart preservation may contribute to the use of hearts from extended criteria donors, thereby expanding the total donor pool.

Role of Mitogen-Activated Protein Kinases in Myocardial Ischemia-Reperfusion Injury during Heart Transplantation

In solid organ transplantation, ischemia/reperfusion (IR) injury during organ procurement, storage and reperfusion is an unavoidable detrimental event for the graft, as it amplifies graft inflammation and rejection. Intracellular mitogen-activated protein kinase (MAPK) signaling pathways regulate inflammation and cell survival during IR injury. The four best-characterized MAPK subfamilies are the c-Jun NH2-terminal kinase (JNK), extracellular signal- regulated kinase-1/2 (ERK1/2), p38 MAPK, and big MAPK-1 (BMK1/ERK5). Here, we review the role of MAPK activation during myocardial IR injury as it occurs during heart transplantation. Most of our current knowledge regarding MAPK activation and cardioprotection comes from studies of preconditioning and postconditioning in nontransplanted hearts. JNK and p38 MAPK activation contributes to myocardial IR injury after prolonged hypothermic storage. p38 MAPK inhibition improves cardiac function after cold storage, rewarming and reperfusion. Small-molecule p38 MAPK inhibitors have been tested clinically in patients with chronic inflammatory diseases, but not in transplanted patients, so far. Organ transplantation offers the opportunity of starting a preconditioning treatment before organ procurement or during cold storage, thus modulating early events in IR injury. Future studies will need to evaluate combined strategies including p38 MAPK and/or JNK inhibition, ERK1/2 activation, pre- or postconditioning protocols, new storage solutions, and gentle reperfusion.

Different ischemic preconditioning regimens affecting preservation injury of intestines

Decreasing ischemia-reperfusion injury in intestinal transplantation is of paramount importance for improving graft recovery and function. This study explores the ability of two ischemic preconditioning (IPC) regimens to reduce preservation injury. Sprague-Dawley rats were divided into 3 groups (n = 11 each). In the controls (group C), intestinal grafts were harvested and preserved. IPC was performed either through 4 cycles of mesenteric ischemia of 4 min each followed by 10 min of reperfusion (group BIPC) or 2 ischemic cycles of 12 min each followed by 10 min of reperfusion (group LIPC). Grafts were stored in histidine-tryptophan-ketoglutarate, and samples were taken 0, 3, 6, 9, 12, 18, and 24 h after preservation. Preservation injury was scored using the Park/Chiu scale. Goblet cells (GC), enteroendocrine cells (EEC) and serotonin-producing EEC (SPEEC) were studied for evaluation of the graft conditions. Group C had the most advanced preservation injury followed by group BIPC. GC count was lowest in group C, followed by BIPC. Comparison between groups BIPC and LIPC showed superior parameters (preservation injury, GC, EEC, and SPEEC) in LIPC. In conclusion, an IPC regimen of 2 ischemic cycles of 12 min each followed by 10 min of reperfusion distinctly decreased the preservation injury of intestinal grafts compared with non-manipulated grafts.

Methods for studying redox cycling of thioredoxin in mediating preconditioning-induced survival genes and proteins

Recent advances in molecular biology provide methods and tools for studying cell signaling pathways underlying hormetic mechanisms produced by radiation hormesis, ischemic, remote ischemic, and chemical preconditioning as well as withholding of nutrients and/or trophic factors. Most of the proposed key signaling pathways of hormetic mechanisms remain to be elucidated. For the investigation of possible role of thiol redox signaling systems in hormesis, a serum deprivation preconditioned human cell model, free radical assays, and molecular biological methods are employed for studying whether free radicals, the NO-cGMP-PKG cell signaling pathway, and the redox protein thioredoxin (Trx) play any roles in the hormetic mechanism against cytotoxicity caused by serum deprivation and also neurotoxin 1-methyl-4-phenyltetrahydropyridinium ion (MPP(+)). This NO-dependent cell signaling pathway of the redox protein Trx may play a key role in the cellular protective mechanism of several potential neuroprotective agents such as S-nitrosoglutathione (GSNO), 17beta-estradiol, selegiline as well as ebeselen, sildenafil, and rasagiline. Consistently, exogenously administrated Trx (<1 microM) provides a concentration-dependent protection for human neuroblasts against MPP(+)-induced oxidative injury. This newly discovered role of the redox protein of Trx in preconditioning-induced cell signaling and protection could lead to the development of new lead compounds for upregulation of Trx and related thiol redox proteins for cell survival, repair, proliferation, and neuronal plasticity.

'Conditioning' the heart during surgery

Coronary heart disease (CHD) is the leading cause of death worldwide. Coronary artery bypass graft (CABG) surgery remains the procedure of choice for coronary artery revascularisation in a large number of patients with severe CHD. However, the profile of patients undergoing CABG surgery is changing with increasingly higher-risk patients being operated upon, resulting in significant morbidity and mortality in this patient group. Myocardial injury sustained during cardiac surgery, most of which can be attributed to acute myocardial ischaemia-reperfusion injury, is associated with worse short-term and long-term clinical outcomes. Clearly, new treatment strategies are required to protect the heart during cardiac surgery in terms of reducing myocardial injury and preserving left ventricular systolic function, such that clinical outcomes can be improved. 'Conditioning' the heart to harness its endogenous cardioprotective capabilities using either brief ischaemia or pharmacological agents, provides a potentially novel approach to myocardial protection during cardiac surgery, and is the subject of this review article.

The Effects of Propofol on Cardiac Function After 4 Hours of Cold Cardioplegia and Reperfusion

OBJECTIVE

To examine whether propofol protects against postischemic myocardial dysfunction and apoptosis during reperfusion after prolonged cold ischemia in isolated rat hearts.

DESIGN

A prospective, randomized, controlled study.

SETTING

A university laboratory.

PARTICIPANTS

Animals.

INTERVENTIONS

The isolated hearts of 40 Sprague-Dawley male rats were perfused with modified Krebs-Hennseleit solution for 15 minutes for a stabilization period and 15 minutes for a perfusion period and then underwent 4 hours of global cold ischemia followed by 60 minutes of reperfusion. Four groups were studied (n = 10 for each group). Ten hearts served as an untreated control group. Propofol (2 micromol/L) treatment was performed only before ischemia in the PRE group, only during reperfusion in the POST group, and both before and after ischemia in the ALL group.

MEASUREMENTS AND MAIN RESULTS

Infusion of propofol during reperfusion improved recovery of left ventricular-developed pressure (LVDP) from 61.2% +/- 8.5% (control) to 86.3% +/- 12.1% (POST) and 74.9% +/- 13.2% (ALL, both p < 0.05), whereas preischemic infusion of propofol (64.3% +/- 9.7%, PRE) did not improve recovery of LVDP. Infusion of propofol during reperfusion significantly reduced the number of apoptotic cells and led to a smaller infarct size than control and PRE groups (p < 0.05, respectively).

CONCLUSIONS

Propofol infusion during the reperfusion period produced a cardioprotective effect and inhibited apoptosis of cardiomyocytes in the ischemia-reperfusion model, with prolonged cold ischemia, in isolated rat hearts.

Organ preconditioning: the past, current status, and related lung studies

Preconditioning (PC) has emerged as a powerful method for experimentally and clinically attenuating various types of organ injuries. In this paper related clinical and basic research issues on organ preconditioning issues were systemically reviewed. Since lung injuries, including ischemia-reperfusion and others, play important roles in many clinical results, including thromboembolism, trauma, thermal injury, hypovolemic and endotoxin shock, reimplantation response after organ transplantation, and many respiratory diseases in critical care. It is of interest to uncover methods, including the PCs, to protect the lung from the above injuries. However, related studies on pulmonary PC are relatively rare and still being developed, so we will review previous literature on experimental and clinical studies on pulmonary PC in the following paragraphs.

Induction of Thioredoxin and Mitochondrial Survival Proteins Mediates Preconditioning-Induced Cardioprotection and Neuroprotection

Delayed cardio- and neuroprotection are observed following a preconditioning procedure evoked by a brief and nontoxic oxidative stress due to deprivation of oxygen, glucose, serum, trophic factors, and/or antioxidative enzymes. Preconditioning protection can be observed in vivo and is under clinical trials for preservation of cell viability following organ transplants of liver. Previous studies indicated that ischemic preconditioning increases the expression of heat-shock proteins (HSPs) and nitric oxide synthase (NOS). Our pilot studies indicate that the treatment of neuronal NOS inhibitor (7-nitroindazole) and 6Br-cGMP blocks and mimics, respectively, preconditioning protection in human neuroblastoma SH-SY5Y cells. This minireview focuses on nitric oxide-mediated cellular adaptation and the related cGMP/PKG signaling pathway in a compensatory mechanism underlying preconditioning-induced hormesis. Both preconditioning and 6Br-cGMP increase the induction of human thioredoxin (Trx) mRNA and protein for cytoprotection, which is largely prevented by transfection of cells with Trx antisense but not sense oligonucleotides. Cytosolic Trx1 and mitochondrial Trx2 suppress free radical formation, lipid peroxidation, oxidative stress, and mitochondria-dependent apoptosis; knock out/down of either Trx1 or Trx2 is detrimental to cell survival. Other recent findings indicate that a transgenic increase of Trx in mice increases tolerance against oxidative nigral injury caused by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Trx1 can be translocated into nucleus and phosphoactivated CREB for a delayed induction of mitochondrial anti-apoptotic Bcl-2 and antioxidative MnSOD that is known to increase vitality and survival of cells in the brain and the heart. In conclusion, preconditioning adaptation or a brief oxidative stress induces a delayed nitric oxide-mediated compensatory mechanism for cell survival and vitality in the central nervous system and the cardiovascular system. Preconditioning-induced adaptive tolerance may be signaling through a cGMP-dependent induction of cytosolic redox protein Trx1 and subsequently mitochondrial proteins such as Bcl-2, MnSOD, and perhaps Trx2 or HSP70.

Ischemic Preconditioning Can Overcome the Effect of Moderate to Severe Cold Ischemia on Concordant Mouse Xeno–Heart Transplants

PURPOSE

Concordant mouse xeno-heart transplants are relatively sensitive to ischemia-reperfusion injury. We investigated the effect of an ischemic preconditioning (IPC) protocol on the functional and biochemical outcome of mouse xenohearts transplanted to the Lewis rat.

MATERIAL AND METHODS

NMRI mice (30 to 40 g) were anesthetized, intubated, and mechanically ventilated. They were subjected either to a IPC protocol leading to an SaO(2) of 70% for 5 minutes followed by normoxia (defined as SaO(2) >90%) for 10 minutes (n = 9) or normoxia only (n = 11). The hearts were then heterotopically transplanted to Lewis rats (220 g). The frequencies of immediate onset and early dysfunction and late dysfunction were registered. The hearts surviving for 6 hours were explanted and the absolute concentrations of phosphocreatine and adenosine triphosphate (ATP) were determined in micromole per gram of heart tissue with high-pressure liquid chromatography. The phosphorylation ratio, PCr/ATP, a known correlate to biochemical and functional outcome, was calculated.

RESULTS

Four of 11 (36.4%) of control hearts experienced immediate onset and early dysfunction versus 0% (0/9) in M hearts subjected to IPC (P = .01). Furthermore, the IPC protocol increased the PCr concentration, 15.08 +/- 1.00 versus 9.04 +/- 2.04 micromol/g in controls (P = .01), and the PCr/ATP ratio, 1.80 +/- 0.17 versus 1.27 +/- 0.21 (NS; P = .06).

CONCLUSIONS

IPC provides a protective PCr overshoot overcoming the short-term effects of moderate to severe ischemic injury on mouse xeno-heart transplants.

Remote preconditioning reduces ischemic injury in the explanted heart by a KATP channel-dependent mechanism

Local and remote ischemic preconditioning (IPC) reduce ischemia-reperfusion (I/R) injury and preserve cardiac function. In this study, we tested the hypothesis that remote preconditioning is memorized by the explanted heart and yields protection from subsequent I/R injury and that the underlying mechanism involves sarcolemmal and mitochondrial ATP-sensitive K(+) (K(ATP)) channels. Male Wistar rats (300-350 g) were randomized to a control (n = 10), a remote IPC (n = 10), and a local IPC group (n = 10). Remote IPC was induced by four cycles of 5 min of limb ischemia, followed by 5 min of reperfusion. Local IPC was induced by four cycles of 2 min of regional myocardial ischemia, followed by 3 min of reperfusion. The heart was excised within 5 min after the final cycle of preconditioning, mounted in a perfused Langendorff preparation for 40 min of stabilization, and subjected to 45 min of sustained ischemia by occluding the left coronary artery and 120 min of reperfusion. I/R injury was assessed as infarct size by triphenyltetrazolium staining. The influence of sarcolemmal and mitochondrial K(ATP) channels on remote preconditioning was assessed by the addition of glibenclamide (10 microM, a nonselective K(ATP) blocker), 5-hydroxydecanoic acid (5-HD; 100 microM, a mitochondrial K(ATP) blocker), and HMR-1098 (30 microM, a sarcolemmal K(ATP) blocker) to the Langendorff preparation before I/R. The role of mitochondrial K(ATP) channels as an effector mechanism for memorizing remote preconditioning was further studied by the effect of the specific mitochondrial K(ATP) activator diaxozide (10 mg/kg) on myocardial infarct size. Remote preconditioning reduced I/R injury in the explanted heart (0.17 +/- 0.03 vs. 0.39 +/- 0.05, P < 0.05) and improved left ventricular function during reperfusion compared with control (P < 0.05). Similar effects were obtained with diazoxide. Remote preconditioning was abolished by the addition of 5-HD and glibenclamide but not by HMR-1098. In conclusion, the protective effect of remote preconditioning is memorized in the explanted heart by a mechanism that involves mitochondrial K(ATP) channels.

Preconditioning the Myocardium: From Cellular Physiology to Clinical Cardiology

Yellon, Derek M., and James M. Downey. Preconditioning the Myocardium: From Cellular Physiology to Clinical Cardiology. Physiol Rev 83: 1113-1151, 2003; 10.1152/physrev.00009.2003.—The phenomenon of ischemic preconditioning, in which a period of sublethal ischemia can profoundly protect the cell from infarction during a subsequent ischemic insult, has been responsible for an enormous amount of research over the last 15 years. Ischemic preconditioning is associated with two forms of protection: a classical form lasting ∼2 h after the preconditioning ischemia followed a day later by a second window of protection lasting ∼3 days. Both types of preconditioning share similarities in that the preconditioning ischemia provokes the release of several autacoids that trigger protection by occupying cell surface receptors. Receptor occupancy activates complex signaling cascades which during the lethal ischemia converge on one or more end-effectors to mediate the protection. The end-effectors so far have eluded identification, although a number have been proposed. A range of different pharmacological agents that activate the signaling cascades at the various levels can mimic ischemic preconditioning leading to the hope that specific therapeutic agents can be designed to exploit the profound protection seen with ischemic preconditioning. This review examines, in detail, the complex mechanisms associated with both forms of preconditioning as well as discusses the possibility to exploit this phenomenon in the clinical setting. As our understanding of the mechanisms associated with preconditioning are unravelled, we believe we can look forward to the development of new therapeutic agents with novel mechanisms of action that can supplement current treatment options for patients threatened with acute myocardial infarction.

Early protective effect of ischemic preconditioning on small intestinal graft in rats

AIM: To investigate the early protective effect of ischemic preconditioning on small intestinal graft in rats.

METHODS: SD rats were randomly divided into the following groups: sham operation group (S group, n = 6), small bowel transplantation group (SBT group, n = 12), ischemic preconditioning plus small bowel transplantation group (ISBT group, n = 12). Heterotopic SBT was performed with a technique modified from that described by Monchik et al When the graft was revascularized successfully and reperfused for 1 h, samples were obtained from the different groups. Laminin was analyzed with immunohistochemical staining. Quantitative analysis of laminin positive signals was performed using image acquiring analysis system. Apoptotic epithelia of small intestinal graft were detected by the TdT-mediated dUTP nick end labeling method. The morphological change of epithelial basement membrane was observed by transmission electron microscopy.

RESULTS: The mean optical density value of laminin positive signals was 39.52 ± 2.60, 13.53 ± 0.44, 25.40 ± 1.79, respectively, in S, SBT and ISBT groups. The average optical density value of laminin positive products in SBT group was sharply lower than that in S group (P < 0.05). However, the mean optical density value of laminin positive products in ISBT group was significantly higher than that in SBT group (P < 0.05). The apoptotic index (AI) in S, SBT and ISBT group was 2.2 ± 0.83,30.8 ± 3.2, 13.2 ± 2.86, respectively. The AI in SBT group was significantly higher than that in S group (P < 0.05), and AI in ISBT group was sharply lower than that in SBT group (P < 0.05). On transmission electron microscopy, the epithelial basement membrane in S group stayed normal, but in SBT group it became disrupted and collapsed, even disappeared. The lesion of epithelial basement membrane in ISBT group was slighter compared with that in SBT group.

CONCLUSION: Ischemic preconditioning has an early protective effect on epithelial cells and extracellur matrix of small intestinal graft. Inhibition of epithelial cell apoptosis may be one of the mechanisms of ischemic preconditioning.

Cardiac preconditioning with 4-h, 17 degrees C ischemia reduces [Ca(2+)](i) load and damage in part via K(ATP) channel opening

Brief ischemia before normothermic ischemia protects hearts against reperfusion injury (ischemic preconditioning, IPC), but it is unclear whether it protects against long-term moderate hypothermic ischemia. We explored in isolated guinea pig hearts 1) the influence of two 2-min periods of normothermic ischemia before 4 h, 17 degrees C hypothermic ischemia on cardiac cytosolic [Ca(2+)], mechanical and metabolic function, and infarct size, and 2) the potential role of K(ATP) channels in eliciting cardioprotection. We found that IPC before 4 h moderate hypothermia improved myocardial perfusion, contractility, and relaxation during normothermic reperfusion. Protection was associated with markedly reduced diastolic [Ca(2+)] loading throughout both hypothermic storage and reperfusion. Global infarct size was markedly reduced from 36 +/- 2 (SE)% to 15 +/- 1% with IPC. Bracketing ischemic pulses with 200 microM 5-hydroxydecanoic acid or 10 microM glibenclamide increased infarct size to 28 +/- 3% and 26 +/- 4%, respectively. These results suggest that brief ischemia before long-term hypothermic storage adds to the cardioprotective effects of hypothermia and that this is associated with decreased cytosolic [Ca(2+)] loading and enhanced ATP-sensitive K channel opening.

Myocardial protection by ischemic preconditioning and delta-opioid receptor activation in the isolated working rat heart

OBJECTIVE

delta-Opioid receptors are involved in the cardioprotective effect of ischemic preconditioning. This study was designed (1) to assess the protective capacities of ischemic preconditioning and the synthetic delta-opioid receptor agonist D-Ala(2)-D-Leu(5) enkephalin (DADLE) in a functionally oriented experimental model of ischemia and reperfusion and (2) to assess whether the effects of both protective measures are similarly blocked by naloxone, a nonspecific delta-opioid receptor antagonist.

METHODS

Sixty-four isolated working rat hearts were subjected to 45 minutes of hypothermic ischemia at 30 degrees C followed by 25 minutes of normothermic reperfusion. Rats were pretreated with DADLE (1 mg/kg body weight intravenously), naloxone (3 mg/kg body weight intravenously), or a combination thereof within 60 minutes before onset of isolated heart perfusion. During the preischemic perfusion period, 8 hearts per group were preconditioned by one cycle of 5 minutes of normothermic global ischemia and subsequent reperfusion whereas another 8 served as nonpreconditioned controls. The postischemic functional recovery of hearts and their creatine kinase leakage were determined.

RESULTS

Pretreatment with DADLE and ischemic preconditioning improved the postischemic recovery of aortic flow when compared with nonpreconditioning (57.7% +/- 4.0% and 60.8% +/- 4.3% vs 40.0% +/- 4.2% of preischemic baseline value, P <.001). Combined pretreatment with DADLE before ischemic preconditioning afforded additional aortic flow recovery compared with pretreatment with DADLE alone (68.6% +/- 3.3% vs 57.7% +/- 4.0% of preischemic baseline value; P =.038). With combined pretreatment, early postischemic creatine kinase release was lower than control in hearts without pretreatment (0.48 +/- 0.11 vs 0.80 +/- 0.12 IU/5 minutes per heart; P =.001). Naloxone abolished the beneficial functional effects of pretreatment with DADLE and ischemic preconditioning.

CONCLUSIONS

Pharmacologic activation of delta-opioid receptors affords improvement of functional protection in isolated working rat hearts similar to that conferred by classic ischemic preconditioning. The combination of both pretreatments reduces ischemic cellular damage and further adds to postischemic functional recovery. These changes are reversed by naloxone, an observation providing evidence that ischemic preconditioning involves signaling through opioid receptors.

Protective effects of ischemic preconditioning on the cold-preserved liver are tyrosine kinase dependent

BACKGROUND

Little data exist regarding the use of ischemic preconditioning before sustained hepatic cold storage. We hypothesized that ischemic preconditioning protects hepatic grafts via a tyrosine kinase-dependent pathway.

METHODS

Six porcine livers underwent routine harvest (control). Five other livers underwent 15 min of in situ ischemia followed by 15 min of reflow before harvest (ischemic preconditioning). Another five livers were pretreated with a tyrosine kinase inhibitor (genistein) before preconditioning. Upon reperfusion and after 2 hours of cold storage, graft function, graft circulatory impairment, and markers of cellular damage were analyzed. Tissue cytoplasmic extracts were analyzed for tyrosine phosphorylation with Western blot. Significance was determined with t tests.

RESULTS

Ischemic-preconditioned grafts demonstrated enhanced bile production, augmented responses to a bile acid challenge, and elevated O2 consumption (P<0.05) compared to controls. Also, preconditioned grafts demonstrated improved hepatic tissue blood flow and decreased hepatic vascular resistance (P<0.005) compared to controls. Endothelial cell preservation (factor VIII immunostain) was improved in preconditioned graft biopsies compared to controls. With genistein pretreatment, all observed improvements returned to control levels. Analysis of cytoplasmic extracts demonstrated an increase in tyrosine phosphorylation before cold ischemia in preconditioned grafts only, but not in control or genistein-pretreated grafts.

CONCLUSIONS

The data indicate that ischemic preconditioning protects the liver from sustained cold ischemia and that tyrosine kinases are involved in preconditioning responses.

Backtable heat-enhanced preconditioning: a simple and effective means of improving function of heart transplants

BACKGROUND

Cardiac harvest teams are usually committed to immediately transfer the explanted donor heart into its cold storage solution. We tested the opposite hypothesis that a brief prestorage episode of heat-enhanced ischemic preconditioning could be protective.

METHODS

Fifty-three isolated isovolumic rat hearts underwent 4 hours of cold (4 degrees C) storage in the Celsior preservation solution and 2 hours of reperfusion. Control hearts were immediately immersed after arrest. In the 3 treated groups, 2 customized thermal probes were first applied onto the left ventricular free wall of the explanted heart at 22 degrees C, 37 degrees C or 42.5 degrees C for 15 minutes before immersion. Each of the selected temperatures were monitored at the probe-tissue interface by a thermocouple.

RESULTS

Whereas base line end-diastolic pressure was set at = 8 mm Hg in all groups, it increased during reperfusion (mean +/- SEM) to 28+/-3, 27+/-3, 17+/-1, and 18+/-2 mm Hg in control, 22 degrees C, 37 degrees C and 42.5 degrees C-heated hearts, respectively (37 degrees C and 42.5 degrees C: p < 0.05 versus controls and 22 degrees C). Slopes of pressure-volume curves featured similar patterns. Likewise, reperfusion dP/dT (mm Hg/s(-1)) was significantly lower in control and 22 degrees C hearts (1,119+/-114 and 1,076+/-125, respectively) than in those undergoing prestorage heating to 37 degrees C and 42.5 degrees C (1,545+/-109 and 1,719+/-111, p < 0.05 and p < 0.01 versus controls and 22 degrees C, respectively). Western blot analysis of LV samples did not demonstrate any upregulation of HSP 72 in either group. Conversely, the involvement of preconditioning was evidenced by the loss of protection in the 42.5 degrees C-heated hearts when, in 2 additional groups, the storage solution was supplemented with either the protein kinase C and tyrosine kinase inhibitors chelerythrine (5 micromol/L) and genistein (50 micromol/L) or the mitochondrial K(ATP) channel inhibitor 5-hydroxydecanoate (200 micromol/L).

CONCLUSIONS

A brief period of postexplant ischemia with enhancement by topical heating ("backtable preconditioning") could be a simple and effective means of improving the functional recovery of heart transplants.

Ischemic preconditioning and nicorandil pretreatment improve donor heart preservation

The present study investigated the effects of ischemic preconditioning (IPC) and nicorandil pretreatment on myocardial storage in a donor heart preservation model. Isolated rat hearts were separated into groups: group 1, non-preconditioned control group; group 2, 2.5 min of normothermic ischemia followed by 15 min of normothermic Langendorff perfusion (one IPC cycle); and group 3, 2 cycles of IPC. All hearts were subsequently stored in University of Wisconsin solution at 4 degrees C for 2, 4 and 6h, and the concentrations of high-energy phosphate metabolites were measured for each time point. Heart function parameters (aortic flow, coronary flow and cardiac output) were measured when the heart was reperfused following the 2, 4 or 6 h of preservation. The effects of nicorandil, an ATP-sensitive potassium channel opener, on heart function following preservation were also evaluated. Nicorandil was injected intravenously before heart harvesting. The results showed that the energy status was well preserved in the IPC groups. The 2-cycle IPC group showed better recovery of heart function following preservation. Pretreatment with nicorandil also improved functional recovery of the heart following preservation. The present study showed that IPC of the rat heart resulted in improved myocardial energy metabolism and functional recovery after hypothermic preservation, and that nicorandil has potential for pharmacological preconditioning in heart preservation for transplantation.

Protective effect of ischemic preconditioning on cold preservation and reperfusion injury associated with rat intestinal transplantation

OBJECTIVE

To define the protective effect of ischemic preconditioning on cold ischemia and reperfusion injury associated with intestinal transplantation, and the role of nitric oxide in this process.

SUMMARY BACKGROUND DATA

Ischemia/reperfusion injury continues to be a significant obstacle in small bowel transplantation. Preconditioning is a mechanism that protects against this injury.

METHODS

To study the capacity of preconditioning to prevent cold ischemia-associated injury and the inflammatory response associated with intestinal transplantation, the authors studied a control group of animals, cold ischemia groups with or without previous preconditioning and with or without previous administration of L-NAME or NONOS, and intestinal transplantation groups with or without previous preconditioning and with or without previous administration of L-NAME or NONOS.

RESULTS

Histologic findings and the release of lactate dehydrogenase into the preservation solution showed that preconditioning protects against cold ischemic preservation-associated injury. Preconditioning also prevented the inflammatory response associated with intestinal transplantation, measured by the above parameters and by neutrophil recruitment in the intestine. Inhibition of nitric oxide eliminates the protective effect.

CONCLUSIONS

Preconditioning protects the intestinal grafts from cold preservation and reperfusion injury in the rat intestinal transplantation model. Nitric oxide is involved in this protection.

Ischemic preconditioning of rat livers against cold storage-reperfusion injury: role of nonparenchymal cells and the phenomenon of heterologous preconditioning

Brief periods of ischemia followed by reperfusion render tissues resistant against subsequent prolonged ischemia, a phenomenon called ischemic preconditioning. The effect of ischemic preconditioning on liver transplantation was investigated in relation to sinusoidal endothelial cell injury and Kupffer-cell activation, which are prominent features of storage and reperfusion injury leading to liver graft failure. Rat livers were preconditioned by 5 or 10 minutes of ischemia and 5 minutes of reperfusion and stored in University of Wisconsin (UW) solution for 30 hours. Livers were then reperfused for 15 minutes with physiological buffer containing trypan blue. Under these conditions, injury occurs predominantly to sinusoidal endothelial cells, reflected by trypan blue staining of nonparenchymal cells in histological sections. Ischemic preconditioning decreased nonparenchymal cell killing by more than 50%. When half the liver was preconditioned, sinusoidal endothelial cells were also protected in the contralateral half. Other stored livers were reperfused with nitroblue tetrazolium, which is converted to insoluble formazan by superoxide radicals. Ischemic preconditioning decreased the intensity of formazan deposition over Kupffer cells. Finally, stored livers were transplanted into nontreated rats. Ischemic preconditioning improved recipient long-term survival after 30 hours of cold ischemic storage in UW solution from 30% to 80% and decreased serum tumor necrosis factor-alpha levels in posthepatic blood 4 hours postoperatively from 98 to 54 pg/mL. In conclusion, ischemic preconditioning protects sinusoidal endothelial cells and suppresses Kupffer-cell activation after storage and reperfusion. As a result, graft survival improves after liver transplantation. Moreover, ischemia to half the liver confers protection to the other half. Such heterologous preconditioning provides a new means to protect liver tissue against ischemia-reperfusion injury without imposing ischemia on the target tissue.

Norepinephrine release after acute brain death abolishes the cardioprotective effects of ischemic preconditioning in rabbit

OBJECTIVE

Brain death (BD) abolishes the infarct-limiting effect of ischemic preconditioning (IP) in rabbits. We wished to define the role of the norepinephrine storm in this observation.

METHODS

Rabbits were randomized into six groups of ten animals each. In control group (CTRL), anaesthetized rabbits were subjected to 30 min left coronary marginal branch occlusion and 90 min reperfusion. In CTRL+IP group, anaesthetized rabbits were preconditioned with a 5-min ischemia and 5-min reperfusion sequence before coronary occlusion. In CTRL+NE+IP group, anaesthetized rabbits received a 10 microg/kg norepinephrine injection 90 min before IP. In BD group, rabbits were subjected to 90 min of BD before coronary occlusion. In BD+IP group, brain-dead rabbits were preconditioned before coronary occlusion. In BD+LA+IP group, rabbits received an intra-arterial bolus injection of an alpha and beta adrenoreceptor blocking agent (labetolol, 1 mg/kg) prior to brain death induction and subsequent preconditioning. BD was induced by rapid inflation of an intracranial balloon. At termination of the experiment, left ventricular volume (LVV), myocardial volume at risk (VAR) and infarct volume (IV) were determined with methylene blue and tetrazolium staining, and measured using planimetry.

RESULTS

LVV was not significantly different among groups. Myocardial VAR/LVV was not significantly different between groups (CTRL, 22.5+/-6.9%; CTRL+IP, 23.3+/-2.2%; CTRL+NE+IP, 25.9+/-12.7%; BD, 19.9+/-4.8%; BD+IP, 21.7+/-3.1%; BD+LA+IP, 23.4+/-5.8%; P=NS). IV/VAR was significantly reduced in the CTRL+IP group as compared with CTRL and CTR+NE+IP groups (12.2+/-1.2 vs. 49.7+/-1.7 and 49.3+/-4.7%; P<0.0001). There was no significant difference in IV/VAR between BD and BD+IP groups. In contrast, IV/VAR was reduced in BD+LA+IP compared to BD and BD+IP groups (13.9+/-5.4 vs. 50.0+/-1.4 and 49.6+/-1.5%; P<0.001).

CONCLUSION

The loss of infarct-limiting effect of IP in brain-dead rabbits is related to the massive release of norepinephrine that occurs as a consequence of BD.

Ischemic preconditioning with opening of mitochondrial adenosine triphosphate-sensitive potassium channels or Na/H exchange inhibition: which is the best protective strategy for heart transplants?

OBJECTIVE

This study was designed to compare ischemic preconditioning with opening of mitochondrial adenosine triphosphate-sensitive potassium channels and Na(+)/H(+) exchange inhibition in an isolated heart model of cold storage, simulating the situation of cardiac allografts.

METHODS

Sixty-seven isolated isovolumic buffer-perfused rat hearts were arrested with and stored in Celsior solution (Imtix-Sangstat) at 4 degrees C for 4 hours before a 2-hour reperfusion. Group I hearts served as controls and were arrested with and stored in Celsior solution. In group II, hearts were preconditioned by two 5-minute episodes of global ischemia, each separated by 5 minutes of reperfusion before arrest with Celsior solution. Group III hearts were arrested with and stored in Celsior solution supplemented with 100 micromol/L of the mitochondrial adenosine triphosphate-sensitive potassium channel opener diazoxide. In group IV, hearts received an infusion of diazoxide (30 micromol/L) during the first 15 minutes of reperfusion. Group V hearts underwent a protocol combining both interventions used in groups III and IV. In group VI, hearts were arrested with and stored in Celsior solution supplemented with 1 micromol/L of the Na(+)/H(+) exchange inhibitor cariporide. Group VII hearts received an infusion of cariporide (1 micromol/L) during the first 15 minutes of reperfusion. In group VIII, hearts underwent a protocol combining both interventions used in groups VI and VII. Group IX hearts were ischemically preconditioned as in group II, and sustained Na(+)/H(+) exchange inhibition during both storage and early reperfusion was used as in group VIII.

RESULTS

On the basis of comparisons of postischemic left ventricular contractility and diastolic function, coronary flow, total creatine kinase leakage, and myocardial water content, values indicative of improved protection were obtained by combining ischemic preconditioning with Na(+)/H(+) exchange inhibition by cariporide given during storage and initial reperfusion. The endothelium-dependent vasodilatory postischemic responses to 5-hydroxytryptamine or acetylcholine and endothelium-independent responses to papaverine were not affected by these interventions.

CONCLUSIONS

These data suggest that cardioprotection conferred by the Na(+)/H(+) exchange inhibitor cariporide is additive to that of ischemic preconditioning and might effectively contribute to improve donor heart preservation during cardiac transplantation.

The preconditioning phenomenon: A tool for the scientist or a clinical reality?

The possibility that an innate mechanism of myocardial protection might be inducible in the human heart has generated considerable excitement and enthusiastic research. The potential to enhance myocardial resistance to ischemic injury in patients suffering the consequences of coronary artery disease has led to studies with more direct clinical relevance. However, in common with many other areas of clinical interest based on advances in basic scientific understanding, early enthusiasm may be disproportionate to ultimate therapeutic significance. There can be little doubt that our understanding of the mechanisms underlying the pathogenesis of ischemia-reperfusion injury has been enhanced significantly by the plethora of research stimulated by interest in endogenous myocardial protection. Direct extrapolation of observations in the laboratory to the cardiology clinic or operating theater is tempting but should be avoided. The results of recent clinical experiments that suggest that preconditioning can protect against ischemia, although encouraging, should be interpreted cautiously, with particular attention to the limitations of the end points available. A reasoned evaluation of recent research should prevent unrealistic expectations and allow improved design of future trials so that this potent adaptive phenomenon can be exploited to its maximum potential.

Opening of mitochondrial potassium channels: a new target for graft preservation strategies?

BACKGROUND

This study was designed to assess the protective effects of the mitochondrial adenosine triphosphate-sensitive potassium channel (KATP) opener diazoxide as an additive to heart preservation solution.

METHODS

Forty isolated isovolumic buffer-perfused rat hearts were divided into four groups. Groups I and III hearts were arrested with and cold-stored in Celsior solution for 4 hr and 10 hr, respectively. In Groups II and IV, hearts underwent a protocol similar to that used in Group I and III, respectively, except that Celsior was supplemented with 100 micromol/L of diazoxide.

RESULTS

The protective effects of diazoxide were primarily manifest as a better preservation of diastolic function and a reduction of myocardial edema. The improvement of postischemic systolic function was observed only after prolonged exposure to diazoxide in Group IV, compared with Group III. The endothelium-dependent and endothelium-independent coronary flow postischemic responses were not affected by the supplementation of Celsior with diazoxide.

CONCLUSIONS

Pharmacologic activation of mitochondrial KATP channels seems to be an effective means of improving preservation of cold-stored hearts, which is consistent with the presumed role of these channels as end effectors of the cardioprotective preconditioning pathway.

Acute brain death abolishes the cardioprotective effects of ischemic preconditioning in the rabbit

BACKGROUND

Myocardial preconditioning with brief coronary artery occlusions before a sustained ischemic period is reported to reduce infarct size. We wished to evaluate whether ischemic preconditioning (IP) is efficient in an experimental brain death (BD) model in the rabbit.

METHODS

Rabbits were randomized into four experimental groups of eight animals each. In the control group (CTRL), anaesthetized rabbits were subjected to 30 min of left coronary marginal branch occlusion and 90 min of reperfusion without any pretreatment. In the CTRL+IP group, anaesthetized rabbits were preconditioned with a 3-min ischemia and 3-min reperfusion sequence before coronary occlusion. In the BD group, rabbits were subjected to 90 min of BD before 30 min of coronary occlusion and 90 min of reperfusion. In the BD+IP group, BD rabbits were preconditioned as in the CTRL+IP group before coronary occlusion. BD was induced by rapid inflation of an intracranial balloon and was validated by clinical and electroencephalographic examinations. At the termination of the experiment, left ventricular volume (LVV), myocardial volume at risk (VAR) and infarct volume (IV) were determined with methylene blue and tetrazolium staining and were measured using planimetry.

RESULTS

LW was not significantly different among the four experimental groups (CTRL, 6.54+/-0.90 cm3; CTRL+IP, 5.92+/-0.60 cm3; BD, 5.87+/-0.81 cm3; BD+IP, 6.16+/-0.95 cm3; P=ns). Furthermore, myocardial VAR, expressed as a percentage of LVV, was not significantly different between groups (CTRL, 20.0+/-4.2%; CTRL+IP, 22.32+/-2.25%; BD, 21.38+/-3.36%; BD+IP, 21.64+/-3.39%; P=NS). IV, expressed as a percentage of VAR, was significantly reduced in the CTRL+IP group compared with the CTRL group (15.76+/-8.47% vs. 49.95+/-1.51%; P<0.0001). In contrast, there was no significant difference in IV, expressed as a percentage of VAR, between the BD and the BD+IP groups (50.0+/-1.52% vs. 49.72+/-1.58%; P=NS).

CONCLUSION

The data indicate that the infarct-limiting effect of IP is lost in BD rabbits. Thus, the clinical potential of IP in the context of organ transplantation seems to be severely compromised.

Overview and future practice patterns in cardiac and pulmonary preservation

Heart and lung transplantation have become standard therapy for many patients with end-stage heart and lung disease. Successful transplantation requires preservation of allografts until they can be implanted and reperfused. In the decades since the transplantation of thoracic organs became a clinical reality, many advances have been made in preoperative donor management, procurement, and preservation techniques. This article summarizes the state of the art in heart and lung preservation and review some of the areas of current research that may lead to improvements in preservation techniques in the future.

Preconditioning: can nature's shield be raised against surgical ischemic-reperfusion injury?

Endogenous myocardial protection refers to the natural defense mechanisms available to the heart to withstand an ischemic injury. So far, these mechanisms have been shown to encompass two phenomena most likely interrelated: ischemic preconditioning and stress protein synthesis. Ischemic preconditioning can be defined as the adaptive mechanism induced by a brief period of reversible ischemia increasing the heart's resistance to a subsequent longer period of ischemia. The therapeutic exploitation of these natural adaptive mechanisms in cardiac surgery is an appealing prospect, as preconditioning could be used before aortic cross-clamping to enhance the current methods of myocardial protection. Two major conclusions emerge from the bulk of experimental data on preconditioning: First, the adaptive phenomenon reduces infarct size after regional ischemia in animal preparations across a wide variety of species but its effects on arrhythmias and on preservation of function after global ischemia are less consistent. This is relevant to cardiac surgery where postbypass pump failure is more often due to stunning than to discrete necrosis. Second, regardless of the various components of the intracellular signaling pathway elicited by the preconditioning stimulus, it seems that the major mechanisms by which this pathway leads to a cardioprotective effect are a slowing of adenosine triphosphate depletion and a limitation of acidosis during the protracted period of ischemia. If the latter is true, then it can reasonably be predicted that these energy-sparing and acidosis-limiting effects may become redundant to those of cardioplegia. From these observations, it can be inferred that preconditioning may find an elective indication in situations where the potential for suboptimal protection increases the risk of necrosis (extensive coronary artery disease, severe left ventricular hypertrophy, long ischemic time, and beating heart operations where occlusion of the target vessels leads to unprotected distal ischemia). Since an ischemic preconditioning stimulus could be clinically undesirable, it is critically important to identify the endogenous mediators of the phenomenon in order to use them therapeutically. One of the most important of these mediators seems to be the adenosine triphosphate-dependent potassium channel. Currently, however, the clinical application of these drugs is hampered by their poor cardioselectivity which could result in untoward systemic vasodilatory effects before cardioprotection becomes manifest. Thus, although the modalities of pharmacologically induced preconditioning still remain to be determined, the concept of therapeutic exploitation of the endogenous adaptive mechanisms of the heart could potentially represent an important adjunct to our current techniques of myocardial protection.

Clinical effects of ischemic preconditioning

A variety of experimental studies have confirmed that preconditioning the myocardium by brief periods of ischemia represents a powerful cardioprotective effect resulting in a reduction of infarct size. After 15 years of research in the experimental laboratory, some evidence shows the existence of preconditioning in human patients with coronary artery disease: repeated balloon inflations before coronary angioplasty induce preconditioning-like effects; moreover, some studies demonstrate better clinical outcome in patients with angina before acute myocardial infarction, resembling a preconditioning effect. So far, a few drugs have been identified as potential mediators of preconditioning, e.g., adenosine, adenosine receptor agonists, and adenosine triphosphate-sensitive potassium channel openers. Before coronary angioplasty and heart surgery, these preconditioning mimetics might be used to protect myocardial tissue by means of preconditioning. Further research is required before preconditioning mimetics could be used for therapy in patients with chronic myocardial ischemia. Possible antipreconditioning effects of several drugs, e.g., sulfonylurea drugs have to be considered in the treatment of patients with coronary artery disease.

Opening of potassium channels: the common cardioprotective link between preconditioning and natural hibernation?

BACKGROUND

The tolerance of hibernating mammals to cold hypoxia is related to a factor similar to agonists of delta-opioid receptors. This study was designed to assess whether activation of these receptors could reproduce the protection conferred by ischemic preconditioning and whether such cardioprotection was similarly mediated by an opening of ATP-sensitive potassium (KATP) channels.

METHODS AND RESULTS

Thirty-two isolated rat hearts were arrested with and stored in Celsior at 4 degrees C for 5 hours before being reperfused for 2 hours. They were divided into 4 equal groups. Group 1 hearts served as controls. In group 2, ischemic preconditioning was elicited by two 5-minute global ischemia periods interspersed with 5 minutes of reperfusion before arrest. In group 3, hearts were pharmacologically preconditioned with a 15-minute infusion of the delta-opioid receptor agonist D-Ala2-D-Leu5-enkephalin (DADLE; 200 micromol/L). In group 4, the protocol was similar to group 3 except that infusion of DADLE was preceded by infusion of the KATP blocker glibenclamide (50 micromol/L). The salutary effects of both forms of preconditioning were primarily manifest as a better preservation of diastolic function, a reduced myocardial edema, and reduced creatine kinase leakage. This protection was abolished by administration of glibenclamide before DADLE.

CONCLUSIONS

These data suggest that activation of delta-opioid receptors improves recovery of cold-stored hearts to a similar extent as ischemic preconditioning, most likely through an opening of KATP channels. This provides a rationale for improving the preservation of hearts for transplantation by pharmacologically duplicating the common pathway to natural hibernation and preconditioning.

Role of ischemic preconditioning on ischemia-reperfusion injury of the lung

STUDY OBJECTIVES

Ischemia-reperfusion injury of the lung frequently occurs after cardiopulmonary bypass, after pulmonary thromboembolectomy, and especially during lung transplantation. The protective effects of preconditioning on the heart, liver, bones, and various other organs have been previously evaluated. In this comparative study, we used isolated guinea pig lungs to show the effects of preconditioning on lung ischemia.

METHODS

The lungs (n = 10 in each group) were mounted on a modified Langendorff perfusion apparatus and perfused by Krebs-Henseleit solution for 30 min. We applied an ischemic preconditioning (5 min ischemia + 5 min perfusion, two times) in the experimental group. After 3 h of normothermic ischemia, the lungs were reperfused for 30 min. Pulmonary artery pressures and malondialdehyde (MDA) and glutathione (GSH) levels of the tissue and the perfusate were measured before and after the ischemic period and also at the end of reperfusion. Electron microscopic evaluation was done on randomly selected lungs of three animals in each group at the end of the experiment.

RESULTS

Both MDA and GSH levels of tissue and perfusate decreased in the experimental group after reperfusion, although the reduction in GSH levels did not reach statistical significance. The increase in pulmonary artery pressure was lower in the preconditioning group after reperfusion.

CONCLUSIONS

Our data showed that ischemic preconditioning of the lung may have a protective effect in ischemic-reperfusion injury.

Pretreatment with a potassium-channel opener before prolonged cardiac storage: an evaluation in an experimental brain death model

BACKGROUND

Pretreatment with a potassium-channel opener has been shown to improve functional recovery after long-term cardioplegic arrest. We evaluated whether pretreatment with the potassium-channel opener cromakalim is beneficial in a more clinically relevant experimental model of brain death in the rabbit.

METHODS

Four groups of rabbits were studied in a 2 x 2 factorial experiment (n = 8 per group). Rabbits were subjected to a sham operation or 90 minutes of brain death induced by inflating a subdurally placed balloon. Thirty minutes before heart explantation, rabbits received either no pretreatment or an intravenous injection of cromakalim, 30 microg/kg. Hearts then received 5 hours' hypothermic storage in St. Thomas' Hospital solution and were assessed on a buffer-perfused isolated heart preparation. Hemodynamic recovery, coronary flow, and creatine kinase release were determined after 60 minutes of reperfusion.

RESULTS

Systolic function and diastolic function were significantly altered in hearts explanted from brain-dead rabbits compared with hearts from rabbits having a sham operation. Cromakalim pretreatment had no significant effect on poststorage systolic or diastolic function of hearts explanted from brain-dead or sham-operation rabbits. Further, cromakalim pretreatment did not affect coronary flow or overall creatine kinase release during reperfusion. CONCLUSIONS; In vivo pretreatment of brain-dead rabbits or anesthetized rabbits with an intravenous injection of cromakalim had no significant effect on functional recovery of or enzymatic release from explanted hearts after 5 hours' hypothermic storage and 60 minutes' reperfusion. These findings underscore the importance of clinically relevant experimental models.

ATP-sensitive potassium channel activation mimics the protective effect of ischaemic preconditioning in the rat isolated working heart after prolonged hypothermic storage

1. Ischaemic preconditioning (IP) can significantly reduce the extent of infarct size, contractile dysfunction and necrosis in hearts from a number of animal species. Activation of ATP-sensitive potassium channels has been implicated in this process. The aims of the present study were to determine the extent to which IP preserves haemodynamic function in the rat isolated working heart model after prolonged hypothermic storage and to examine the involvement of activation of potassium channels in this process. 2. Hearts from Wistar rats were perfused on a Langendorff apparatus. After stabilization in working mode, baseline measurements of heart rate, aortic flow, coronary flow and cardiac output were performed. Hearts were randomized to one of six treatment groups: (i) untreated control; (ii) IP; (iii) 3 min perfusion with 200 mumol/L pinacidil; (iv) pinacidil vehicle; (v) 3 min perfusion with 10 mumol/L glibenclamide before IP; and (vi) 3 min perfusion with glibenclamide then pinacidil. Hearts were stored in an extracellular-based preservation solution for 6 or 12 h at 2-3 degrees C, remounted on the perfusion apparatus, stabilized as before and then haemodynamic measurements were repeated, after which time heart water contents were determined. 3. Recovery of haemodynamic function was markedly enhanced in the IP and pinacidil-treated groups compared with untreated and vehicle controls. These beneficial effects were completely blocked by glibenclamide. These results suggest that strategies for activating potassium channels in donor hearts may protect organs during hypothermic storage prior to transplantation.

Preconditioning prevents myocardial stunning after cardiac transplantation

BACKGROUND

Preconditioning has been shown to reduce myocardial stunning after reversible global ischemia. To determine whether preconditioning improves functional recovery after cardiac transplantation, 16 sheep were randomly assigned to a preconditioning protocol or to a control group.

METHODS

Preconditioning was achieved with 5 minutes of global ischemia followed by 10 minutes of reperfusion. The heart was then arrested with 1 L of crystalloid cardioplegia, explanted, stored in a transport cooler, and then transplanted into recipient sheep. The total ischemia time was 2 hours. Pressure-volume loops were used to calculate preload recruitable stroke work, the maximum elastance, and diastolic compliance. Linear regression analysis was used to determine the preload recruitable stroke work, maximum elastance, and diastolic compliance-and end-diastolic volume relationship. The area under the regression curve for preload recruitable stroke work was defined as the preload recruitable stroke work area. Biopsies were taken for high-energy phosphates.

RESULTS

Systolic function, represented by preload recruitable stroke work area, was preserved after cardiac transplantation in preconditioned animals. Maximum elastance and diastolic compliance were unaffected by preconditioning or ischemia. High-energy phosphates were better preserved in preconditioned animals.

CONCLUSION

Preconditioning prevented myocardial stunning and preserved high-energy phosphates after experimental cardiac transplantation.

Preconditioning with cromakalim improves long-term myocardial preservation for heart transplantation

BACKGROUND

Myocardial preservation for heart transplantation relies on hyperkalemic cardiac arrest and hypothermic storage. Our study investigated whether pretreatment with a potassium-channel opener (cromakalim) before prolonged storage in an extracellular fluid improves left ventricular recovery.

METHODS

Rabbit hearts were submitted to 6-hours' cold storage and assessed on a blood-perfused isolated heart preparation. Hemodynamic recovery, enzyme release (creatine kinase and lactate dehydrogenase), and adenine nucleotide content were determined. Five groups were tested: control (n=6), no ischemia; UW group (n=7), hearts arrested with and stored in University of Wisconsin solution; STH group (n=5), hearts arrested with and stored in St. Thomas' Hospital solution; cromakalim group (n=6), hearts pretreated with cromakalim (30 microg/kg) before arrest with and storage in St. Thomas' Hospital solution; and glibenclamide group (n=5), hearts pretreated with cromakalim followed by glibenclamide (a potassium-channel blocker) before arrest with and storage in St. Thomas' Hospital solution.

RESULTS

Hemodynamic recovery was improved and enzyme release was lower in the UW group than in the STH group. Compared with the STH group, the group pretreated with cromakalim had significantly decreased left ventricular end-diastolic pressures, increased left ventricular developed pressures, increased maximal values of positive and negative rates of rise of left ventricular pressure, and increased time constant of isovolumetric relaxation. Hemodynamic recovery was similar in the UW group and cromakalim groups. Glibenclamide did not abolish the effects of cromakalim. None of the protocols affected myocardial energy stores.

CONCLUSION

Pretreatment with cromakalim affords additional protection to that provided by cardioplegic arrest and prolonged cold storage using an extracellular solution. The intracellular mechanisms involved remain to be determined.

Effectiveness of ischemic preconditioning on long-term myocardial preservation

BACKGROUND

This study was designed to assess whether the protective effect of ischemic preconditioning can be adapted for myocardium undergoing 6 hr of ischemia.

METHODS

Eighteen isolated rat hearts were perfused with oxygen-bicarbonated Krebs-Henseleit buffer in the Langendorff mode for 35 min (group A, controls) or perfused in the Langendorff apparatus for 20 min, followed by 5 min of global normothermic ischemia and 10 min of buffer perfusion (group B, preconditioning) or followed by two cycles of 2.5 min of global normothermic ischemia plus 5 min of buffer perfusion (group C, preconditioning). The hearts were then arrested and preserved for 6 hr with Bretschneider's histidine-tryptophan-potassium cardioplegic solution at 4 degrees C, followed by 30 min of reperfusion. Recovery of cardiac function, postischemic enzyme leakage, and intracellular calcium concentration were compared.

RESULTS

After 6 hr of ischemia, the hearts that underwent preconditioning in groups B and C showed better recovery of left ventricular developed pressure (P<0.05), a lower end-diastolic pressure level (P<0.05), less leakage of creatine kinase, and a lower intracellular calcium concentration than those in group A. There were no statistical differences in the rate of recovery of coronary flow.

CONCLUSIONS

Our study demonstrated that ischemic preconditioning improves myocardial functional recovery after 6 hr of hypothermic preservation in the isolated rat heart. Preconditioning might be useful for preserving the heart against long-term ischemia/reperfusion injury.

Cardioprotective efficacy of ischemic preconditioning on long-term myocardial ischemia

This study was designed to assess whether the protective effect of ischemic preconditioning can be adapted for myocardium undergoing 6 h of no-flow ischemia. Twelve isolated rat hearts were either perfused with oxygen-bicarbonated Krebs-Henseleit buffer in the Langendorff mode for 35 min (n=6), or perfused in the same way for 20 min, following 5 min of global normothermic ischemia and 100 min of buffer-perfusion (n=6). The 12 hearts were then preserved for 6 h in HTK solution at 4 degrees C, followed by 30 min of reperfusion. Recovery of cardiac function, metabolic activity and intracellular free calcium concentration were compared between the two groups. After 6 h ischemia, the hearts that underwent preconditioning showed better recovery of left ventricular developed pressure (P<0.01), a lower end-diastolic pressure level (P<0.05), less creatine kinase leakage and a lower calcium concentration. There was no statistical difference in the recovery rate of coronary flow and leakage rate of LDH between the two groups. In conclusion, this experiment demonstrates that ischemic preconditioning improved myocardial functional recovery after 6 h of hypothermic ischemic preservation in the isolated rat heart. Preconditioning might be a potential mechanism for preserving the heart against long-term ischemia/reperfusion injury.