Total ischemia in dog hearts, in vitro 2. High energy phosphate depletion and associated defects in energy metabolism, cell volume regulation, and sarcolemmal integrity

Saving zone of stasis in burn wounds by nanoliposomal Mg-ATP

ATP is a crucial molecule for every energy-dependent process in cells. In ischemic tissues, ATP production declines, and it finally results in cell death. One of the most common strategies in burn wound management is saving the zone of ischemia. In the current study, Mg-ATP-containing nanoliposomes were formulated and studied in vitro and in vivo. The particle size of the vesicles was between 50 and 100 nm and the mean zeta potential was -4.05 ± 0.52 mV as evaluated by dynamic light scattering and Zeta sizer instrument, respectively. The encapsulation efficiency of ATP in the nanoliposomes was found to be 9.3%. The morphology and size of nanoliposomes were further studied by transmission electron microscopy. The standard MTT assay revealed no cytotoxicity of the nanoliposomes when tested on the rat fibroblast cells. Forty rats were randomly divided into four groups (N = 10 each). Burn wounds were created by burn comb model on the back of the rats and the zone of stasis in each group was treated every 12 h for 3 days by injecting them with the Mg-ATP-nanoliposomes. Control samples included empty nanoliposomes, unencapsulated Mg-ATP and the Krebs-Henseleit buffer. Laser Doppler flowmetry results revealed that blood perfusion in the zone of ischemia in rats treated with Mg-ATP-nanoliposomes was more than in the other groups (p < 0.05). Histopathology revealed saving zone of stasis by Mg-ATP-nanoliposomes. Findings obtained in this study demonstrated that the formulated Mg-ATP-nanoliposome has the potential to save the stasis zone in burn wounds.

Myocardial Injury, Troponin Release and Cardiomyocyte Death in Brief Ischemia, Failure and Ventricular Remodeling

Troponin released from irreversibly injured myocytes is the gold standard biomarker for the rapid identification of an acute coronary syndrome. In acute myocardial infarction, necrotic cell death is characterized by sarcolemmal disruption in response to a critical level of energy depletion after more than 15-minutes of ischemia. While troponin I and T are highly specific for cardiomyocyte death, high-sensitivity assays have demonstrated that measurable circulating levels of troponin are present in the majority of normal subjects. In addition, transient as well as chronic elevations have been demonstrated in many disease states not clearly associated with myocardial ischemia. The latter observations have given rise to the clinical concept of myocardial injury. This review will summarize evidence supporting the notion that circulating troponin levels parallel the extent of myocyte apoptosis in normal ventricular remodeling and in pathophysiological conditions not associated with infarction or necrosis. It will review the evidence that myocyte apoptosis can be accelerated by both diastolic strain from elevated ventricular preload as well as systolic strain from dyskinesis after brief episodes of ischemia too short to cause a critical level of myocyte energy depletion. We then show how chronic, low rates of myocyte apoptosis from endogenous myocyte turnover, repetitive ischemia or repetitive elevations in LV diastolic pressure can lead to significant myocyte loss in the absence of neurohormonal stimulation. Finally, we posit that the differential response to strain-induced injury in heart failure may determine whether progressive myocyte loss and HFrEF or interstitial fibrosis and HFpEF become the heart failure phenotype.

Ischemia-Reperfusion Injuries Assessment during Pancreas Preservation

Maintaining organ viability between donation and transplantation is of critical importance for optimal graft function and survival. To date in pancreas transplantation, static cold storage (SCS) is the most widely practiced method of organ preservation. The first experiments in ex vivo perfusion of the pancreas were performed at the beginning of the 20th century. These perfusions led to organ oedema, hemorrhage, and venous congestion after revascularization. Despite these early hurdles, a number of factors now favor the use of perfusion during preservation: the encouraging results of HMP in kidney transplantation, the development of new perfusion solutions, and the development of organ perfusion machines for the lung, heart, kidneys and liver. This has led to a resurgence of research in machine perfusion for whole organ pancreas preservation. This review highlights the ischemia-reperfusion injuries assessment during ex vivo pancreas perfusion, both for assessment in pre-clinical experimental models as well for future use in the clinic. We evaluated perfusion dynamics, oedema assessment, especially by impedance analysis and MRI, whole organ oxygen consumption, tissue oxygen tension, metabolite concentrations in tissue and perfusate, mitochondrial respiration, cell death, especially by histology, total cell free DNA, caspase activation, and exocrine and endocrine assessment.

Attenuating loss of cardiac conduction during no-flow ischemia through changes in perfusate sodium and calcium

Myocardial ischemia leads to conduction slowing, cell-to-cell uncoupling, and arrhythmias. We previously demonstrated that varying perfusate sodium (Na⁺) and calcium (Ca²⁺) attenuates conduction slowing and arrhythmias during simulated ischemia with continuous perfusion. Cardioprotection was selectively associated with widening of the perinexus, a gap junction adjacent nanodomain important to ephaptic coupling. It is unknown whether perfusate composition affects the perinexus or ischemic conduction during nonsimulated ischemia, when coronary flow is reduced or halted. We hypothesized that altering preischemic perfusate composition could facilitate perinexal expansion and attenuate conduction slowing during global ischemia. To test this hypothesis, ex vivo guinea pig hearts (n = 49) were Langendorff perfused with 145 or 153 mM Na⁺ and 1.25 or 2.0 mM Ca²⁺ and optically mapped during 30 min of no-flow ischemia. Altering Na⁺ and Ca²⁺ did not substantially affect baseline conduction. Increasing Na⁺ and decreasing Ca²⁺ both lowered pacing thresholds, whereas increasing Ca²⁺ narrowed perinexal width (W_p). A least squares mean estimate revealed that reduced perfusate Na⁺ and Ca²⁺ resulted in the most severe conduction slowing during ischemia. Increasing Na⁺ alone modestly attenuated conduction slowing, yet significantly delayed the median time to conduction block (10 to 16 min). Increasing both Na⁺ and Ca²⁺ selectively widened W_p during ischemia (22.7 vs. 15.7 nm) and attenuated conduction slowing to the greatest extent. Neither repolarization nor levels of total or phosphorylated connexin43 correlated with conduction slowing or block. Thus, perfusate-dependent widening of the perinexus preserved ischemic conduction and may be an adaptive response to ischemic stress.NEW & NOTEWORTHY Conduction slowing during acute ischemia creates an arrhythmogenic substrate. We have shown that extracellular ionic concentrations can alter conduction by modulating ephaptic coupling. Here, we demonstrate increased extracellular sodium and calcium significantly attenuate conduction slowing during no-flow ischemia. This effect was associated with selective widening of the perinexus, an intercalated disc nanodomain and putative cardiac ephapse. These findings suggest that acute changes in ephaptic coupling may serve as an adaptive response to ischemic stress.

Redox states of hemoglobin determine left ventricle pressure recovery and activity of mitochondrial complex IV in hypoxic rat hearts

Cardiovascular effects were reported to occur in humans and in animal models during transfusion with hemoglobin (Hb)-based oxygen therapeutics. The effects of Hb's iron redox states on cardiac parameters during hypoxia/reoxygenation are however poorly defined. We hypothesize that acute exposures to ferric Hb during hypoxia leads to cardiomyocyte injury and an impaired left ventricular response accompanied by cardiac mitochondrial bioenergetic dysfunction. Recovery of left ventricular functions in an isolated rat heart Langendorff perfusion system was observed following perfusion with ferrous but not with ferric Hb. Ferric Hb induced the development of heart lesions, and impairment of the respiratory chain complex activity. Under normoxia, a sharp decline in cardiac parameters was observed following co-perfusion of low (20 μM) and high (100 μM) ascorbic acid (Asc) with ferrous Hb. This trend continued with ferric Hb co-perfusion, but only at the higher concentration of Asc. These observations suggest that perfusion of the hypoxic heart with ferric Hb increases oxidative stress thereby resulting in cardiac dysfunction. Intervention with Asc to reduce ferric Hb may offer a strategy to control Hb toxicity; however, timing of administration, and dosage of Asc may require individual optimization to target specific redox forms of Hb.

Hyperpolarized [1,4-13C2]Fumarate Enables Magnetic Resonance-Based Imaging of Myocardial Necrosis

OBJECTIVES

The aim of this study was to determine if hyperpolarized [1,4-13C2]malate imaging could measure cardiomyocyte necrosis after myocardial infarction (MI).

BACKGROUND

MI is defined by an acute burst of cellular necrosis and the subsequent cascade of structural and functional adaptations. Quantifying necrosis in the clinic after MI remains challenging. Magnetic resonance-based detection of the conversion of hyperpolarized [1,4-13C2]fumarate to [1,4-13C2]malate, enabled by disrupted cell membrane integrity, has measured cellular necrosis in vivo in other tissue types. Our aim was to determine whether hyperpolarized [1,4-13C2]malate imaging could measure necrosis after MI.

METHODS

Isolated perfused hearts were given hyperpolarized [1,4-13C2]fumarate at baseline, immediately after 20 min of ischemia, and after 45 min of reperfusion. Magnetic resonance spectroscopy measured conversion into [1,4-13C2]malate. Left ventricular function and energetics were monitored throughout the protocol, buffer samples were collected and hearts were preserved for further analyses. For in vivo studies, magnetic resonance spectroscopy and a novel spatial-spectral magnetic resonance imaging sequence were implemented to assess cardiomyocyte necrosis in rats, 1 day and 1 week after cryo-induced MI.

RESULTS

In isolated hearts, [1,4-13C2]malate production became apparent after 45 min of reperfusion, and increased 2.7-fold compared with baseline. Expression of dicarboxylic acid transporter genes were negligible in healthy and reperfused hearts, and lactate dehydrogenase release and infarct size were significantly increased in reperfused hearts. Nonlinear regression revealed that [1,4-13C2]malate production was induced when adenosine triphosphate was depleted by >50%, below 5.3 mmol/l (R2 = 0.904). In vivo, the quantity of [1,4-13C2]malate visible increased 82-fold over controls 1 day after infarction, maintaining a 31-fold increase 7 days post-infarct. [1,4-13C2]Malate could be resolved using hyperpolarized magnetic resonance imaging in the infarct region one day after MI; [1,4-13C2]malate was not visible in control hearts.

CONCLUSIONS

Malate production in the infarcted heart appears to provide a specific probe of necrosis acutely after MI, and for at least 1 week afterward. This technique could offer an alternative noninvasive method to measure cellular necrosis in heart disease, and warrants further investigation in patients.

The Physiopathology of Cardiorenal Syndrome: A Review of the Potential Contributions of Inflammation

Inter-organ crosstalk plays an essential role in the physiological homeostasis of the heart and other organs, and requires a complex interaction between a host of cellular, molecular, and neural factors. Derangements in these interactions can initiate multi-organ dysfunction. This is the case, for instance, in the heart or kidneys where a pathological alteration in one organ can unfavorably affect function in another distant organ; attention is currently being paid to understanding the physiopathological consequences of kidney dysfunction on cardiac performance that lead to cardiorenal syndrome. Different cardiorenal connectors (renin-angiotensin or sympathetic nervous system activation, inflammation, uremia, etc.) and non-traditional risk factors potentially contribute to multi-organ failure. Of these, inflammation may be crucial as inflammatory cells contribute to over-production of eicosanoids and lipid second messengers that activate intracellular signaling pathways involved in pathogenesis. Indeed, inflammation biomarkers are often elevated in patients with cardiac or renal dysfunction. Epigenetics, a dynamic process that regulates gene expression and function, is also recognized as an important player in single-organ disease. Principal epigenetic modifications occur at the level of DNA (i.e., methylation) and histone proteins; aberrant DNA methylation is associated with pathogenesis of organ dysfunction through a number of mechanisms (inflammation, nitric oxide bioavailability, endothelin, etc.). Herein, we focus on the potential contribution of inflammation in pathogenesis of cardiorenal syndrome.

Cardioprotection with halogenated gases: how does it occur?

Numerous studies have studied the effect of halogenated agents on the myocardium, highlighting the beneficial cardiac effect of the pharmacological mechanism (preconditioning and postconditioning) when employed before and after ischemia in patients with ischemic heart disease. Anesthetic preconditioning is related to the dose-dependent signal, while the degree of protection is related to the concentration of the administered drug and the duration of the administration itself. Triggers for postconditioning and preconditioning might have numerous pathways in common; mitochondrial protection and a decrease in inflammatory mediators could be the major biochemical elements. Several pathways have been identified, including attenuation of NFκB activation and reduced expression of TNFα, IL-1, intracellular adhesion molecules, eNOS, the hypercontraction reduction that follows reperfusion, and antiapoptotic activating kinases (Akt, ERK1/2). It appears that the preconditioning and postconditioning triggers have numerous similar paths. The key biochemical elements are protection of the mitochondria and reduction in inflammatory mediators, both of which are developed in various ways. We have studied this issue, and have published several articles on cardioprotection with halogenated gases. Our results confirm greater cardioprotection through myocardial preconditioning in patients anesthetized with sevoflurane compared with propofol, with decreasing levels of troponin and N-terminal brain natriuretic peptide prohormone. The difference between our studies and previous studies lies in the use of sedation with sevoflurane in the postoperative period. The results could be related to a prolonged effect, in addition to preconditioning and postconditioning, which could enhance the cardioprotective effect of sevoflurane in the postoperative period. With this review, we aim to clarify the importance of various mechanisms involved in preconditioning and postconditioning with halogenated gases, as supported by our studies.

ATP, Creatine Phosphate and Glycogen Content in Human Myocardial Biopsies: Markers for the Efficacy of Cardioprotection During Aorto-Coronary Bypass Surgery

Measurements of the myocardial content of ATP, creatine phosphate and glycogen provide a sensitive marker of the effect of inevitably global ischemia on myocardial tissue during aorto-coronary bypass surgery and give insight in the efficacy of various cardioprotective techniques. Continuous aortic cross clamping for performance of the distal anastomoses with multidose St. Thomas cardioplegia did not result in significant changes in the myocardial ATP, creatine phosphate and glycogen content. In contrast, hypothermic intermittent crossclamping resulted in a significant reduced tissue content of these markers of myocardial ischemia.

Native Myocardial T1 Mapping, Are We There Yet?

T1 or longitudinal relaxation time is one of the very fundamental magnetic resonance imaging (MRI) time constants and a tissue characterizing parameter. Only during the last decade did it become possible to quantify T1 values of the myocardium through T1 mapping. Evolving from only region of interest analysis and long acquisition times to the pixel-based parametric mapping and short breath-hold sequences, T1 mapping is reaching maturity among cardiac magnetic resonance (CMR) techniques. Both inversion recovery methods such as MOdified Look-Locker Inversion (MOL-LI) and Shortened MOLLI (ShMOLLI) and saturation recovery methods such as Saturation recovery Single-Shot Acquisition (SASHA) are available for T1 quantification with variable degrees of accuracy, precision, and reproducibility. Native (non-contrast) T1 values increase with edema, amyloid deposition, and fibrosis, while they decrease in fat or iron deposition in the myocardium. These features enabled significant expansion of the clinical applications of native T1 mapping where it provides high sensitivity and specificity and even acts as a disease biomarker or a predictor of prognosis. It is of particular usefulness in diffuse myocardial diseases where conventional CMR techniques might be deceiving. A brighter future for the technique is expected if certain challenges are to be faced, examples of which are the need for standardization of normal values, acquisition techniques, and improving analysis tools.

LC/MS-based polar metabolite profiling reveals gender differences in serum from patients with myocardial infarction

Myocardial infarction (MI), a leading cause of death worldwide, results from prolonged myocardial ischemia with necrosis of myocytes due to a blood supply obstruction to an area of the heart. Many studies have reported gender-related differences in the clinical features of MI, but the reasons for these differences remain unclear. In this study, we applied ultra-performance liquid chromatography/quadrupole time-of-flight mass spectrometry (UPLC/Q-TOF MS) and various statistical methods-such as multivariate, pathway, and correlation analyses-to identify gender-specific metabolic patterns in polar metabolites in serum from healthy individuals and patients with MI. Patients with diagnosed MI (n=68), and age- and body mass index-matched healthy individuals (n=68), were included in this study. The partial least-squares discriminant analysis (PLS-DA) model was generated from metabolic profiling data, and the score plots showed a significant gender-related difference in patients with MI. Many pathways were associated with amino acids and purines; amino acids, acylcarnitines, and purines differed significantly between male and female patients with MI. This approach could be utilized to observe gender-specific metabolic pattern differences between healthy controls and patients with MI.

Roles of collateral arterial flow and ischemic preconditioning in protection of acutely ischemic myocardium

The extent and rate at which necrosis develops in experimental acute myocardial infarction in the dog heart is presented together with an analysis of the role played by protective mechanisms in myocyte death. Preconditioning with ischemia delays but does not prevent myocyte death. Arterial collateral flows exceeding 30% of control flow essentially prevent myocyte death, while lesser amounts of collateral flow delay myocyte death to a variable extent. Flows of <0.09mlmin(-1)g(-1) wet exert no protective effect. Cell death occurs as quickly as it does with zero flow. Electrocardiography provides a means of detection of the preconditioned state in the dog heart in that the amount of ST elevation observed during the preconditioning episode is reduced during subsequent episodes of ischemia. Also, marked depression of arterial collateral flow can be detected by an increase in the duration of the QRS segment.

T1 mapping in ischaemic heart disease

A unique feature of cardiac magnetic resonance is its ability to characterize myocardium. Proton relaxation times, T1, T2, and T2* are a reflection of the composition of individual tissues, and change in the presence of disease. Research into T1 mapping has largely been focused in the study of cardiomyopathies, but T1 mapping also shows huge potential in the study of ischaemic heart disease. In fact, the first cardiac T1 maps were used to characterize myocardial infarction. Robust high-resolution myocardial T1 mapping is now available for use as a clinical tool. This quantitative technique is simple to perform and analyse, minimally subjective, and highly reproducible. This review aims to summarize the present state of research on the topic, and to show the clinical potential of this method to aid the diagnosis and treatment of patients with ischaemic heart disease.

Intracellular ATP delivery using highly fusogenic liposomes

Healthy cells must maintain a high content of adenosine triphosphate (ATP) because almost all energy-requiring processes in cells are driven, either directly or indirectly, by hydrolysis of ATP. During ischemia or hypoxia, reduced blood flow or disturbed oxygen supply results in the disrupted balance of energy production and utilization, and depletion of high-energy phosphates is the fundamental cause of cell damage. Direct intravenous infusion of high-energy phosphates, such as adenosine triphosphate (ATP), has not produced a consistent result because strongly charged molecules like ATP normally cannot pass the cell membrane in sufficient quantities to satisfy tissue metabolic requirements. Furthermore, the half-life of free ATP in blood circulation is very short, limiting its efficacy as a bioenergetic substrate. We have developed a new technique for intracellular delivery of high-energy phosphate into normal or ischemic cells by using specially formulated, highly fusogenic, unilamellar lipid vesicles that contain magnesium-ATP. In vitro studies indicated a rapid fusion with the endothelial cells, protection of endothelial cells, and cardiomyocytes during ischemia. In vivo studies have shown enhanced full-thickness skin wound healing in various animal models. This technique has the potential to reduce or eliminate many detrimental effects caused by ischemia or hypoxia.

Unique mode of cell death in freshly isolated adult rat ventricular cardiomyocytes exposed to hydrogen peroxide

To address whether adult rat ventricular cardiomyocytes (ARVCs) exposed to oxidant stress die via apoptosis (secondarily by necrosis) or primarily by necrosis, we exposed ARVCs to hydrogen peroxide (H2O2; 0.1-100 microM) for up to 24 h and then compared them with isoproterenol-induced apoptotic and Triton X-induced necrotic controls. Cellular shrinkage preceded plasma membrane disruption, reflected by trypan blue uptake in ARVCs exposed to lower concentrations of H2O2 (<1 microM; an apoptotic pattern), but the order was reversed in cells exposed to higher concentrations of H2O2 (>1 microM; a necrotic pattern). DNA fragmentation, caspase-3 activation, mitochondrial membrane potential preservation, and ATP preservation were all apparent in ARVCs treated with low H2O2 (0.5 microM), but not in those treated with high H2O2 (10 microM). In addition, electron microscopy revealed unique morphology in H2O2-treated ARVCs; i.e., the nuclei had a homogeneous ground glass-like appearance that was never accompanied by chromatin condensation. Apparently, high concentrations of H2O2 caused primary necrosis in ARVCs, whereas low concentrations induced biochemically comparable apoptosis, although the latter did not satisfy the morphological criteria of apoptosis. These findings caution against the use of oxidant stress, H2O2 in particular, as an inducer of apoptosis in ARVCs.

Energy metabolism in the reversible and irreversible phases of severe myocardial ischemia

In summary, myocardial ischemia is associated with the progressive depletion of HEP and the adenine nucleotide pool. Anaerobic glycolysis is essential for energy production in the severely ischemic myocyte and accounts for 80% of the HEP utilized by severely or totally ischemic myocardium. However, the rate of anaerobic glycolysis is too slow to prevent the progressive depletion of ATP. Anaerobic glycolysis stops entirely prior to the complete utilization of glycogen. Without remaining HEP stores or HEP production from anaerobic glycolysis, HEP utilization no longer can occur. This point occurs in vivo after about 40 minutes of severe ischemia and coincides with the onset of cell death. Modest depletion of ATP due to brief periods of transient ischemia may not cause cell death, but is associated with partial depletion of the adenine nucleotide pool. The slow repletion of this pool may be responsible for prolonged depression of contractile function.

Morphological and biochemical characterization of basal and starvation-induced autophagy in isolated adult rat cardiomyocytes

Autophagy is simultaneously a mode of programmed cell death and an important physiological process for cell survival, but its pathophysiological significance in cardiac myocytes remains largely unknown. We induced autophagy in isolated adult rat ventricular cardiomyocytes (ARVCs) by incubating them in glucose-free, mannitol-supplemented medium for up to 4 days. Ultrastructurally, intracellular vacuoles containing degenerated subcellular organelles (e.g., mitochondria) were markedly apparent in the glucose-starved cells. Microtubule-associated protein-1 light chain 3 was significantly upregulated among the glucose-starved ARVCs than among the controls. After 4 days, glucose-starved ARVCs showed a significantly worse survival rate (19+/-5.2%) than the controls (55+/-8.3%, P<0.005). Most dead ARVCs in both groups showed features of necrosis, and the rate of apoptosis did not differ between the groups. Two inhibitors of autophagy, 3-methyladenine (3-MA) and leupeptin, significantly and dose-dependently reduced the viability of both control and glucose-starved ARVCs and caused specific morphological alterations; 3-MA reduced autophagic findings, whereas leupeptin greatly increased the numbers and the sizes of vacuoles that contained incompletely digested organelles. The knockdown of the autophagy-related genes with small interfering RNA also reduced the glucose-starved ARVCs viability, but rapamycin, an autophagy enhancer, improved it. Reductions in the ATP content of ARVCs caused by glucose depletion were exacerbated by the inhibitors while attenuated by rapamycin, suggesting that autophagy inhibition might accelerate energy depletion, leading to necrosis. Taken together, our findings suggest that autophagy in cardiomyocytes reflects a prosurvival, compensatory response to stress and that autophagic cardiomyocyte death represents an unsuccessful outcome due to necrosis.

Effects of acute vagal nerve stimulation on the early passive electrical changes induced by myocardial ischaemia in dogs: heart rate-mediated attenuation

Parasympathetic activity during acute coronary artery occlusion (CAO) can protect against ischaemia-induced malignant arrhythmias; nonetheless, the mechanism mediating this protection remains unclear. During CAO, myocardial electrotonic uncoupling is associated with autonomically mediated immediate (i.e. type 1A) arrhythmias and can modulate pro-arrhythmic dispersion of repolarization. Therefore, the effects of acutely enhanced or decreased cardiac parasympathetic activity on early electrotonic coupling during CAO, as measured by myocardial electrical impedance (MEI), were investigated. Anaesthetized dogs were instrumented for MEI measurements, and left circumflex coronary arterial occlusions were performed in intact (CTRL) and vagotomized (VAG) animals. The CAO was followed by either vagotomy (CTRL) or vagal nerve stimulation (VNS, 10 Hz, 10 V) in the VAG dogs. Vagal nerve stimulation was studied in two additional sets of animals. In one set heart rate (HR) was maintained by pacing (220 beats min(-1)), while in the other set bilateral stellectomy preceded CAO. The MEI increased after CAO in all animals. A larger MEI increase was observed in vagotomized animals (+85 +/- 9 Omega, from 611 +/- 24 Omega, n = 16) when compared with intact control dogs (+43 +/- 5 Omega, from 620 +/- 20 Omega, n = 7). Acute vagotomy during ischaemia abruptly increased HR (from 155 +/- 11 to 193 +/- 15 beats min(-1)) and MEI (+12 +/- 1.1 Omega, from 663 +/- 18 Omega). In contrast, VNS during ischaemia (n = 11) abruptly reduced HR (from 206 +/- 6 to 73 +/- 9 beats min(-1)) and MEI (-16 +/- 2 Omega, from 700 +/- 44 Omega). These effects of VNS were eliminated by pacing but not by bilateral stellectomy. Vagal nerve stimulation during CAO also attenuated ECG-derived indices of ischaemia (e.g. ST segment, 0.22 +/- 0.03 versus 0.15 +/- 0.03 mV) and of rate-corrected repolarization dispersion [terminal portion of T wave (TPEc), 84.5 +/- 4.2 versus 65.8 +/- 5.9 ms; QTc, 340 +/- 8 versus 254 +/- 16 ms]. Vagal nerve stimulation during myocardial ischaemia exerts negative chronotropic effects, limiting early ischaemic electrotonic uncoupling and dispersion of repolarization, possibly via a decreased myocardial metabolic demand.

MRI relaxation fluctuations in acute reperfused hemorrhagic infarction

MRI evaluations of intramyocardial hemorrhage in acute infarction have relied on T(2) and T(2)(*) shortening only. We propose a more comprehensive evaluation of hemorrhagic infarction based on the concept that fluctuations in T(2) and T(1) relaxation in acute reperfused infarction will reflect transient edema and hemoglobin oxidative denaturation to uncompartmentalized methemoglobin. Anteroapical infarction was created via percutaneous balloon in young swine (22-25 kg, N = 12). T(2), T(1), diastolic wall thickness (DWT), and the Gd-DTPA partition coefficient (lambda) were measured on days 0, 2, and 7. DWT was elevated at 1 hr postreperfusion (128% +/- 53%, P = 0.0001), and alleviated on days 2 and 7 (48% +/- 10%, P = 0.008; 53% +/- 24%, P = 0.003). T(2) and T(1) elevations were coincident with early edema (DeltaT(2) = 55% +/- 24%, P < 0.0001; DeltaT(1) = 27% +/- 18%, P < 0.04). T(2) and T(1) were nearly normal on day 2 (DeltaT(2) = 8% +/- 8%, P = 0.27; DeltaT(1) = 0% +/- 1%, P = 0.65). On day 7, T(2) increased while T(1) decreased (DeltaT(2) = 27% +/- 16%, P = 0.005; DeltaT(1) = -14% +/- 10%, P = 0.02). Lambda was elevated by >150% at all time points (P < or = 0.002). Histology verified hemorrhagic injury. T(1) and T(2) fluctuations are consistent with transient edema, as well as hemoglobin oxidative denaturation to decompartmentalized methemoglobin. This methodological development may broaden our understanding of hemorrhagic microvascular injury and improve its detection in clinical populations.

Interstitial purine metabolites in hearts with LV remodeling

The myocardial ATP concentration is significantly decreased in failing hearts, which may be related to the progressive loss of the myocardial total adenine nucleotide pool. The total myocardial interstitial purine metabolites (IPM) in the dialysate of interstitial fluid could reflect the tissue ATP depletion. In rats, postmyocardial infarction (MI) left ventricular (LV) remodeling was induced by ligation of the coronary artery. Cardiac microdialysis was employed to assess changes of IPM in response to graded beta-adrenergic stimulation with isoproterenol (Iso) in myocardium of hearts with post-MI LV remodeling (MI group) or hearts with sham operation (sham group). The dialysate samples were analyzed for adenosine, inosine, hypoxanthine, xanthine, and uric acid. LV volume was greater in the MI group (2.2 +/- 0.2 ml/kg) compared with the sham group (1.3 +/- 0.2 ml/kg, P < 0.05). Infarct size was 28 +/- 4%. The baseline dialysate level of uric acid was higher in the MI group (18.9 +/- 3.4 micromol) compared with the sham group (4.6 +/- 0.7 micromol, P < 0.01). During and after Iso infusion, the dialysate levels of adenosine, xanthine, and uric acid were all significantly higher in the MI group. Thus the level of IPM is increased in hearts with postinfarction LV remodeling both at baseline and during Iso infusion. These results suggest that the decreased myocardial ATP level in hearts with post-MI LV remodeling may be caused by the chronic depletion of the total adenine nucleotide pool.

Relationships between hemodynamic parameters and myocardial energy and antioxidant status in heart transplantation

The relationships between high-energy phosphate levels, oxidative insult and mechanical function represent a key point in heart transplantation and related post-ischemic functional recovery. We evaluated myocardial purine compounds and glutathione antioxidant defence mechanism during 19 heart transplant operations. Heart biopsies were taken before harvesting on beating heart (t1), at the end of cold static preservation (t2) and 30 min after implantation and reperfusion (t3); perchloric extracts of the tissue were analyzed by capillary electrophoresis (CE). Correlation analyses were performed with hemodynamic parameters evaluated 90 min after aortic declamping (T90), 6 h following admission in intensive care unit (T6A) and 1 d post-operation (D1). We evidenced that AMP levels measured at T1 negatively correlate with both cardiac index (CI) and oxygen delivery index (DO2I) evaluated at T6A, respectively. The same behavior was evident plotting IMP levels measured at T3 with CI and DO2I evaluated at D1. After t2 the nucleotide/(nucleoside + base) ratio was in positive correlation with hemodynamic parameters at T6A. Energy charge and GSH/GSSG ratio measured before harvesting were in positive correlation with DO2I evaluated at T90. The present research shows that despite the complexity of the high-energy phosphate metabolism and that of the events associated to a clinical heart transplantation, there are some parameters that, besides reflecting the degree of myocardial preservation, also represents predictive parameters for the following organ functional recovery. It also suggests that heart preservation strategies should carefully take into account the sub-optimal nature of the donor heart at the time of procurement, through a broad spectrum of purine compound and glutathione antioxidant system measurements.

PCr overshoot': a study of the duration in canine myocardium

The phosphocreatine (PCr) overshoot is a well-documented phenomenon and is readily observable by 31P MRS. In addition, a second 31P MRS observation during ischemia with reperfusion is a diminution in ATP levels. Combining these two as the 'PCr Overshoot' the PCr/ATP ratio may provide an index of viability. However little information is available regarding the duration of this 'overshoot'. For this approach to be useful clinically, the duration of this phenomenon must be ascertained. An open chest canine model of 12 min of ischemia followed by reperfusion (6h) was used. A 2 cm surface coil was sutured to the myocardium and spectra were acquired at 4.7 T. Gated spectra were acquired in <2.5 min with an interpulse delay of 5 s. Integrals of the PCr and ATP (beta) resonances were analyzed using a line-fitting routine. Overall, the PCr signal increased from 22.0+/-0.8 to 25.5+/-0.9 and ATP decreased from 11.7+/-0.4 to 10.0+/-0.4 (arbitrary units). The PCr remained elevated for the entire 6h period and the percentage increase was 15.9%. The ATP remained depleted for the entire 6h period and the percentage decrease was 17.0%. Thus, the clinically relevant and readily observable PCr/ATP is a product of both an increase in PCr and a decrease in ATP for a calculated net increase in PCr/ATP of 39.6%. The PCr/ATP ratio of the ischemia group for baseline, ischemia, 6h reflow, were: 2.33+/-0.18, 1.04+/-0.29 and 3.22+/-0.21. We demonstrate that the 'PCr overshoot' is readily observable and can be monitored noninvasively and nondestructively for 6h. Therefore, the 'PCr overshoot' may be a viable marker of reversible injury in this model and may prove to be applicable for detecting myocardial viability in patients.

Cardiac transplantation following a 24-h preservation using a perfusion apparatus

BACKGROUND

We developed a new apparatus for heart preservation and have already reported successful transplantation following 12 h of preservation using this apparatus. The efficacy of coronary perfusion with an oxygenated Celsior solution was investigated through transplantation following 24 h of preservation using the apparatus.

MATERIALS AND METHODS

After being harvested, grafts were preserved with a combination of immersion in a 4 degrees C Celsior solution and perfusion with an oxygenated Celsior solution using the apparatus in the coronary perfusion (CP) group and simply immersed in a 4 degrees C Celsior solution in the simple immersion(SI) group. beta-Adenosine triphosphate (beta-ATP), phosphocreatine (Pcr), and inorganic phosphate (P(i)) levels and myocardial pH (pH(i)) were measured immediately after the heart was excised and at 12 and 24 h after preservation. Following preservation, orthotopic transplantation was performed. Cardiac function was measured 2 h after weaning from cardiopulmonary bypass (CPB).

RESULTS

beta-ATP/P(i), Pcr/P(i), and pH(i) levels were significantly higher in the CP group than in the SI group at 12 and 24 h after preservation. Four of six animals in the CP group and two of six in the SI group were successfully weaned from CPB. The recovery rates of cardiac function were better in the CP group than in the SI group.

CONCLUSION

Twenty-four hours of heart preservation may be possible with a combination of immersion in a 4 degrees C Celsior solution and perfusion with an oxygenated Celsior solution using the perfusion apparatus.

The Effect of Coronary Perfusion with an Oxygenated Celsior Solution on 12-hour Cardiac Preservation

Celsior is a new extracellular-type cardiac preservation solution. We recently developed an apparatus for preservation using low-pressure continuous coronary perfusion. The purpose of this study was to investigate the efficacy of coronary perfusion with an oxygenated Celsior solution using the new apparatus for prolonged cardiac preservation. Adult mongrel dogs weighing 9-13 kg were divided into two groups: the coronary perfusion group (CP; n = 5) and the simple immersion group (SI; n = 7). The coronary vascular beds were washed out with a 4 degrees C Celsior solution following cardiac arrest using the same solution, and their hearts were excised. In the CP group, the graft was immersed in a 4 degrees C Celsior solution and perfused with the same oxygenated solution. In the SI group, the graft was simply immersed in a 4 degrees C Celsior solution. beta-adenosine triphosphate (beta-ATP), phosphocreatine (Pcr), inorganic phosphate (Pi) levels and myocardial pH (pHi) were measured immediately after excising the heart, and at 3, 6, and 12 hours after preservation. beta-ATP, Pcr, and Pi values were expressed as a percentage of control values, which were measured immediately after excising the heart. beta-ATP/Pi and Pcr/Pi levels were significantly higher in the CP group than in the SI group at 6 and at 12 hours after preservation. The pHi levels during preservation were significantly higher in the CP group than in the SI group. Low-pressure hypothermic coronary perfusion with an oxygenated Celsior solution is effective for long-term heart preservation. </hea

Contrast-enhanced MRI for the assessment of myocardial viability after permanent coronary artery occlusion

Previous studies in a model of ischemia/reperfusion using a constant infusion of Gd-DTPA have shown that distribution volume (lambda) is increased in infarcted myocardial tissue. This study examined this technique in the setting of permanent coronary artery occlusion. Ten beagles underwent permanent occlusion of a coronary artery for 2 days (N = 3), 1 week (N = 4), or 3 weeks (N = 3). Imaging was performed at 2 days and, depending on the length of occlusion, 1 week, 2 weeks, and 3 weeks to follow changes in lambda in vivo. At sacrifice, (201)Tl was injected and the extent of the hyperenhanced region was compared to pathology. lambda was increased in infarcted tissue by 2 days post occlusion and this increase persisted for 3 weeks. At sacrifice, lambda correlated strongly with (201)Tl uptake (r = -0.86 to -0.95, P < 0.05; i.e., lambda increased in infarcted tissue) and the size of the hyperenhanced region was comparable to pathological infarct size (slope 1.006, r = 0.96, P < 0.0001). Thus, beyond 2 days after coronary occlusion, MRI, during a constant infusion of Gd-DTPA, can assess myocardial viability regardless of the success of reperfusion. Magn Reson Med 44:309-316, 2000.

Capillary electrophoresis in the evaluation of ischemic injury: simultaneous determination of purine compounds and glutathione

An understanding of tissue energy metabolism and antioxidant status is of major interest in the field of organ preservation for transplantation. Nucleotide and glutathione are indicators of cell damage occurring during ischemia and reperfusion. A high performance capillary electrophoresis (HPCE) method with UV detection (185 nm) for the simultaneous analysis of intracellular free ribonucleotides, nucleosides, bases and glutathione (oxidized and reduced form) in myocardial tissues is described. The method does not involve thiol derivatization. The separations were carried out in an uncoated fused-silica capillary, 60 cm long, 52.5 cm to detector, 75 microm ID, with 20 mM Na-borate buffer, pH 10.00, at 20 kV voltage and reading at 185 nm. Injection was hydrostatic for 12 s and total analysis time was 20 min. The technique enables optimum separation of all the compounds examined and has a resolution similar to that of HPLC analysis, with the advantage of fast simultaneous measurement of cell nucleotide metabolism and redox state, not possible with HPLC.

Efficient limitation of intracellular edema and sodium accumulation by cardioplegia is dissociated from recovery of rat hearts from cold ischemic storage

Energy deficiency and disturbances of sodium and water homeostasis are considered as mechanisms of injury during hypothermic preservation of cardiac muscle. The present study attempts to characterize the effect of potassium (K+) and magnesium (Mg2+) cardioplegia on these mechanisms. Cellular parameters were measured by multinuclear NMR spectroscopy in isolated rat hearts during 12 h of ischemia at 4 degrees C and 2 h of normothermic reperfusion with an isoosmotic Krebs-Henseleit (KH) solution. Potassium and magnesium cardioplegia (a) reduced the rate of ATP hydrolysis and cellular acidification during early stages of ischemia; (b) caused an early cessation of the phase of fast sodium influx after 40 min (P<0.001 vs 120 min with KH); (c) reduced intracellular sodium accumulation to 148-165 micromol/gdw after 12 h (P<0.01 vs 268+/-15 micromol/gdw with KH); (d) decreased ischemic volumes to 2.7+/-0.1 and 2.8+/-0.1 ml/gdw after 8 and 12 h of storage, respectively (P<0.005 v 3.0 and 3.3 ml/gdw with KH). Quantitative analysis of these parameters showed that both hypothermia and cardioplegia increased the relative contribution of sodium to intracellular water accumulation by a factor of 2-2.5. In view of the marked reduction in absolute sodium and water contents, the data indicate that cold cardioplegia limits the increase in intracellular osmolarity. Myocardial mechanical and metabolic recoveries, and cellular viability deteriorated during prolongation of the ischemic period from 8 to 12 h in all experimental groups (P<0.005). Reperfusion was efficient in reversing intracellular sodium and water accumulation in hearts stored with cardioplegia, in contrast to hearts stored in KH. Magnesium, but not potassium cardioplegia, lowered interstitial water contents (P<0.01 v KH), increased intracellular magnesium concentrations (P<0.001), improved mechanical and metabolic recoveries (P<0.01) and cellular viability (P<0.001). These results indicate (a) cardioplegia reduces intracellular sodium (by approximately 46%) and water accumulation (by 66%) during cold ischemia; (b) both hypothermia and cardioplegia limit the rise in intracellular osmolarity and increase the contribution of sodium to cellular swelling; (c) intracellular sodium and water contents were dissociated from myocardial viability and recovery from cold ischemia in potassium and magnesium cardioplegic solutions. It is concluded that intracellular sodium and water accumulation are not dominant factors in determination of cardiac outcome from ischemia.

Development of cardiac sensitivity to oxygen deficiency: comparative and ontogenetic aspects

Hypoxic states of the cardiovascular system are undoubtedly associated with the most frequent diseases of modern times. They originate as a result of disproportion between the amount of oxygen supplied to the cardiac cell and the amount actually required by the cell. The degree of hypoxic injury depends not only on the intensity and duration of the hypoxic stimulus, but also on the level of cardiac tolerance to oxygen deprivation. This variable changes significantly during phylogenetic and ontogenetic development. The heart of an adult poikilotherm is significantly more resistant as compared with that of the homeotherms. Similarly, the immature homeothermic heart is more resistant than the adult, possibly as a consequence of its greater capability for anaerobic glycolysis. Tolerance of the adult myocardium to oxygen deprivation may be increased by pharmacological intervention, adaptation to chronic hypoxia, or preconditioning. Because the immature heart is significantly more dependent on transsarcolemmal calcium entry to support contraction, the pharmacological protection achieved with drugs that interfere with calcium handling is markedly altered. Developing hearts demonstrated a greater sensitivity to calcium channel antagonists; a dose that induces only a small negative inotropic effect in adult rats stops the neonatal heart completely. Adaptation to chronic hypoxia results in similarly enhanced cardiac resistance in animals exposed to hypoxia either immediately after birth or in adulthood. Moreover, decreasing tolerance to ischemia during early postnatal life is counteracted by the development of endogenous protection; preconditioning failed to improve ischemic tolerance just after birth, but it developed during the early postnatal period. Basic knowledge of the possible improvements of immature heart tolerance to oxygen deprivation may contribute to the design of therapeutic strategies for both pediatric cardiology and cardiac surgery.

Biochemical consequences of electrical pacing in ischemic-reperfused isolated rat hearts

It is still unclear if performance recovery in postischemic hearts is related to their tissue level of high-energy phosphates before reflow. To test the existence of this link, we monitored performance, metabolism and histological damage in isolated, crystalloid-perfused rat hearts during 20 min of low-flow ischemia (90% coronary flow reduction) and reflow. To prevent interference from different ischemia times and perfusing media compositions, the ischemic ATP level was varied by changing energy demand (electrical pacing at 330 min(-1)). Under full coronary flow conditions, work output, as well as ATP and phosphocreatine contents were the same in control, spontaneously contracting (n = 23) and paced (n = 21) hearts. During low-flow ischemia, the higher work output (p < 0.0001) in paced hearts decreased their tissue content of ATP, phosphocreatine and total adenylates and purines (p < 0.05), as opposed to maintained values in control hearts. During reflow, the recovery of mechanical performance and O2 uptake was 94 +/- 5% and 110 +/- 9% (p = NS vs. baseline) in controls, vs. 71 +/- 5% and 74 +/- 6% in paced hearts (p < 0.004 vs. baseline). The levels of ATP and total adenylates and purines remained constant in control, but were markedly depressed (p < 0.05 vs. baseline) in paced hearts. Phosphocreatine+creatine was the same in both groups. These data, together with the observed lack of creatine kinase leakage and of structural damage, indicate that myocardial recovery during reflow reflects the tissue level of ATP, phosphocreatine and total adenylates and purines during ischemia, regardless of physical cell damage.

High-energy phosphates metabolism and recovery in reperfused ischaemic hearts

BACKGROUND

The aim of this study was to assess how coronary flow, oxygen supply and energy demand affect myocardial ATP, phosphocreatine and their metabolites during oxygen shortage and recovery.

METHODS

Isolated rat hearts were exposed for 20 min to either low-flow ischaemia or hypoxaemia at the same oxygen supply, followed by return to baseline conditions (20 min). Seventy-three hearts were divided into four groups: ischaemic or hypoxaemic, spontaneously beating or paced to increase energy demand.

RESULTS

During O2 shortage, myocardial performance was less in ischaemic, spontaneously beating hearts (SpIs), than in the other groups (14 +/- 1% of baseline vs. 25-48%). Consequently, the tissue levels of ATP, total adenylates and phosphocreatine were maintained in SpIs, in contrast to marked decreases in the other groups. Upon reflow, the recovery of performance and of myocardial ATP was 94 +/- 5% in SpIs (P = NS vs. baseline) compared with 64-85% (P < 0.05 vs. baseline) in the other groups. The degree of recovery was positively related to the ischaemic contents of ATP (P = 0.03) and adenylates (P = 0.001), but not to that of phosphocreatine (P = NS).

CONCLUSION

The maintenance of the ATP pool under low oxygen supply conditions is essential for good recovery. The most important factors that determine the ATP pool size are the energy demand, which increases the formation of diffusible ATP catabolites, and the coronary flow, which removes these catabolites, rather than the oxygen supply per se.

Myocardial ischemic injury and purine metabolism in patients undergoing coronary artery bypass

OBJECTIVES

High-energy phosphates and their catabolic products were determined in myocardium during coronary artery bypass surgery with blood cardioplegic reperfusion in order to evaluate the effects of aortic cross-clamping and reoxygenation on myocardial purine metabolism.

DESIGN AND METHODS

Transmural left ventricular biopsy specimens were taken with ITu-Cut biopsy needles, before aortic cross-clamping, before cross-clamp removal and after 30' of reperfusion; perchloric extracts of the material were analyzed for nucleotide content by capillary zone electrophoresis (CZE). The CZE procedure used separates the complete spectrum of purine metabolites in myocardial extracts obtained from 0.6-8.6 mg biopsy material.

RESULTS

The basal values of ATP/ADP ratio and energy charge were low, IMP content was high. After the ischemic period, ATP levels further decreased and IMP, nucleosides and bases accumulated. After reperfusion, nucleoside and base basal levels, but not energy charge, were restored to some extent.

CONCLUSIONS

The study arises the problem of myocardial preservation during heart surgery. In this investigation, capillary electrophoresis was an extremely adaptable technique for the evaluation of ischemic injury and could be useful in studying the effects of cardioplegic solutions.

Apoptosis in heart failure

A characteristic feature of heart failure is the progressive worsening of ventricular function over months or years despite the absence of clinically apparent intercurrent adverse events. The mechanism or mechanisms responsible for this hemodynamic deterioration are not known but may be related to progressive intrinsic contractile dysfunction of residual viable cardiac myocytes, or to ongoing degeneration and loss of myocytes, or both. This report will address the concept of ongoing cardiac myocyte loss that may occur during the course of evolving heart failure viewed from the perspective of apoptosis or "programmed cell death" as the potential mediator of cardiac muscle cell loss. In recent years, several studies have shown that constituent myocytes of failed explanted human hearts and hearts of animals with experimentally induced heart failure undergo apoptosis. Recent studies have shown that cardiac myocyte apoptosis also occurs after acute myocardial infarction, as well as in the hypertrophied heart and the aging heart, conditions frequently associated with the development of heart failure. Considerable work has also been conducted and novel concepts advanced to explain potential molecular triggers of cardiac myocyte apoptosis in heart failure. Although available data support the existence of myocyte apoptosis in the failing heart, questions essential to our understanding of the importance of myocyte apoptosis in this disease process remain unanswered. Lacking are studies aimed at identifying physiological factors inherent to heart failure that trigger myocyte apoptosis. Also lacking are studies that address the importance of myocyte apoptosis in the progression of left ventricular dysfunction. If loss of cardiac myocytes through apoptosis can be shown to be an important contributor to the progression of heart failure, and if factors that trigger apoptosis in the heart can be identified, such knowledge can potentially lead to the development of novel therapeutic modalities aimed at preventing, or at the very least retarding, the process of progressive ventricular dysfunction and the ultimate transition toward end-stage, intractable heart failure.

Effect of acetylsalicylic acid on metabolism and contractility in the ischemic reperfused heart

The effect of acetylsalicylic acid (ASA) on high-energy phosphates (adenosine triphosphate: ATP, creatine phosphate: CrP, inorganic phosphate: Pi) and intracellular pH during myocardial ischemia and reperfusion was studied using phosphorus 31-nuclear magnetic resonance (31P-NMR) in the isolated rabbit hearts. Coronary flow, left ventricular systolic developed pressure (LV Dev.P) and left ventricular end-diastolic pressure (LVEDP) were also measured. Langendorff hearts perfused at 37 degrees C with the perfluorochemical emulsion Fluosol-43 were subjected to 15 min and 30 min of zero-flow ischemia and to 15 min of low-flow ischemia (coronary perfusion pressure = 20 mmHg) followed by 65 min of reperfusion (control, Group I). ASA (0.28 mmol/L) was infused either for the entire experimental period from beginning 45 min prior to ischemia (Group II) and infused immediately after reperfusion (Group III). During ischemia, Group II showed a significant suppression of the decrease in the ATP level and pH with both zero-flow and low-flow ischemia compared to those in the other groups, and moreover the increase in Pi and the decrease in CrP in low-flow ischemia were also suppressed. In Group III, the ATP level during reperfusion was significantly higher than that in Group I, but was not significantly different from that in 30 min zero-flow ischemia. In 30 min zero-flow ischemia, Pi, CrP and coronary flow after reperfusion in Group II tended to recover to preischemic values. There were no differences in LV Dev.P among the 3 groups. In conclusion, ASA has a protective effect on myocardial high-energy phosphates during ischemia and reperfusion in rabbit hearts.

Regional myocardial blood flow, glucose utilization and contractile function before and after revascularization and ultrastructural findings in patients with chronic coronary artery disease

In patients with chronic coronary artery disease, follow-up measurements of myocardial blood flow, metabolism and function were correlated with histology. In 41 patients with chronic coronary artery disease and a severely stenosed left anterior descending coronary artery, a positron emission tomographic (PET) flow/metabolism study and nuclear angiography were performed immediately before and 3 months after bypass surgery. Biopsies were taken from the left ventricular anterior wall at the time of surgery. Control biopsies were taken from donor hearts for cardiac transplantation and from hearts of patients with a defect of the atrial septum. A significant improvement of flow (P<0.01) and regional contractile function (P<0.01) was observed in the mismatch group. Glucose utilization was significantly lower (P<0.001) as compared to preoperative values. The group with preserved flow and the PET match group revealed no significant changes in flow, metabolism or function. Control biopsies revealed significantly less myolytic cells as compared to biopsies taken from both match and mismatch groups (P<0.01) and less fibrosis as compared to biopsies taken from the match group (P<0.01). Postoperatively, linear relationships were found between flow and both % fibrosis (r = 0.71, P<0.001) and regional anterior ejection fraction (r = 0.7, P<0.001). Only mismatch areas revealed significant recovery of both flow and function after revascularization with a disappearance of enhanced glucose uptake. The better linear correlation between flow and % fibrosis after surgery as compared to preoperatively was probably due to improvement of flow values in the mismatch group.

R56865 is antifibrillatory in reperfused ischemic guinea-pig hearts, even when given only during reperfusion

R56865 was previously characterized as an inhibitor of Na and Ca overload that has beneficial effects during ischemia and reperfusion. An isolated guinea-pig heart preparation was subjected to 60 minutes of ischemia and 60 minutes of reperfusion. R56865 was given before ischemia and with the onset of reperfusion, applying different dosing schedules, including an initial loading dose. R56865 below 0.1 mumol/l had no cardiodepressant effects in normoxic hearts and at 0.1 mumol/l reduced left ventricular pressure marginally. The onset of ischemic contracture was delayed only at this concentration. R56865 given before ischemia potently inhibits delayed sustained fibrillation occurring during reperfusion in the concentration range between 0.01 mumol/l and 0.1 mumol/l. Analysis of cellular Na+, K+, and Ca2+ concentrations revealed that R56865 substantially improves the ionic homeostasis of myocardial cells. Most importantly, the compound also reduced the incidence of delayed sustained fibrillation when given at the onset of reperfusion. R56865 was most effective when fast equilibration of drug with tissue was achieved by giving an initial loading dose. In particular, the cellular Na+ and Ca2+ contents were improved using this dosing scheme. The results are compatible with the classification of R56865 as an inhibitor of Na+ and Ca2+ overload.

The electrophysiology of ischemia and cardioplegia: implications for myocardial protection

The primary goal of modern cardioplegia is to protect the heart during the periods of cardiac arrest and global ischemia that are required to perform cardiac surgery. In order to achieve this, cardioplegic solutions must be able to arrest rapidly the electrical activity of the heart. An understanding of the electrophysiology of cardioplegia is critical to an adequate understanding of its basic mechanisms of action. This article reviews recent advances in our understanding of the electrophysiological changes seen during ischemia and cardioplegia. Although 10 years ago, depolarization and repolarization were attributed to changes in membrane resistance, advances in molecular biology have elucidated that the mechanism of the action potential is governed by ionic transport across hydrophobic lipid membranes through carefully regulated pores formed by members of an extended family of ion channel proteins. There also have been great strides in our understanding of the heart's electrophysiological response to ischemia. One of the most dramatic responses to ischemia is a profound shortening of the cardiac action potential, which has been shown to be cardioprotective by limiting calcium influx into the cell. ATP-sensitive potassium channels have been confirmed to play a critical role in the action potential shortening seen during ischemia. Drugs that open these channels have been shown to limit infarct size, attenuate myocardial stunning, and ameliorate reperfusion injury. Recent work has demonstrated that these drugs may be effective cardioplegic agents.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of global ischemia on the sarcolemmal ATPases in the rat heart

To elucidate the effect of global ischemia on the energy utilizing processes, regarding the molecular principles, the kinetic and thermodynamic properties of the sarcolemmal ATPases were investigated in the rat heart. The activation energy for hydrolysis of ATP during ischemia was higher when the reaction was catalyzed by Ca-ATPase or Mg-ATPase. For the Na,K-ATPase reaction, no changes in the activation energy were observed. With respect to the enzyme kinetics, ischemia in a time-dependent manner induced important alterations in KM and Vmax values of Na,K-ATPase, Ca-ATPase and Mg-ATPase. The Vmax value decreased significantly already after 15 min of ischemia, and it also remained low after 30, 45 and 60 min for all 3 enzymes. The significant diminution of KM values occurred later in the 30th min for Ca-ATPase, in the 45th min for Na,K-ATPase. The observed drop in KM indicates the increase in the affinity of the enzymes to substrate, suggesting thus the adaptation to ischemic conditions on the molecular level. This effect could be attributed to some conformational changes of the protein molecule in the vicinity of the ATP-binding site developing after longer duration of ischemia.

Acute pharmacologic preconditioning as a new concept and alternative approach for prevention of skeletal muscle ischemic necrosis

The phenomenon of ischemic preconditioning for augmentation of ischemic tolerance has been well documented in the myocardium of common laboratory animals and human cardiomyocytes. The cellular mechanism of ischemic preconditioning is unclear, but adenosine is most likely the mediator in the rabbit, dog, pig and human. We have demonstrated recently that the protective effect of ischemic preconditioning and adenosine against ischemic injury can also be induced in pig skeletal muscles [116]. We speculate that adenosine is a potential treatment modality for prevention of skeletal muscle ischemic injury in vascular and musculoskeletal reconstructive surgery and in muscle and limb procurement for transplantation in the future. It is hoped that this review will stimulate workers at other laboratories to join the adventure in exploring the cellular mechanism and clinical application of adenosine for augmentation of skeletal muscle ischemic tolerance.

The contraction state of myofibrils during global ischemia and after reperfusion following different forms of cardiac arrest. Correlation with metabolic parameters in the canine heart

This study was undertaken in order to obtain information on the mode of reaction of the contractile apparatus after different forms of cardiac arrest, global ischemia and reperfusion, as well as on possible correlations between the contraction state of myofibrils and biochemical parameters. During the survival time, before the level of 3 mumol/gww creatine phosphate (CP) is reached, the contraction state shows only minor changes. During the revival time in which ATP tissue concentrations decay to 4 mumol/gww, the contribution of ATP, lactate, anorganic phosphate (Pa) and acidosis to the degree of relaxation depends on the method of cardiac arrest. At defined biochemical values, the degree of relaxation is comparable after aortic cross clamping (ACC) and St. Thomas perfusion, but significantly different compared to HTK perfusion. Thus, during the revival time, the relaxation of sarcomeres depends predominantly on the composition of the solutions used for cardiac arrest. The re-entry of contraction below 3 mumol/gww ATP is correlated with the ATP concentration, independent of the form of cardiac arrest. Reperfusion after HTK or St. Thomas cardioplegia and reversible ischemia leads to the focal formation of contraction bands, which do not occur during ischemia. This contraction state is significantly more pronounced after reperfusion of St. Thomas arrested hearts. Thus, the contraction state of myofibrils is influenced not only by alterations in metabolite concentrations, but also by the composition of cardioplegic solutions and by the characteristic conditions (sufficient energy, oxygen and Calcium) during reperfusion.

Kinetic and thermodynamic properties of membrane bound Ca-ATPase with low affinity to calcium in cardiac sarcolemma; response to global ischemia of the heart

Thermodynamic and kinetic properties of membrane bound Ca-ATPase with low affinity to calcium in cardiac sarcolemma were investigated with respect to the effect of global ischemia on the heart. Energy barrier for ATP hydrolysis catalyzed by the Ca-ATPase was slightly higher in hearts subjected to ischemia, as it was evident from increased values of activation energy. Ischemia also induced a time dependent decrease in the activity and maximum velocity (Vmax) value of Ca-ATPase. The depression of enzyme activity was evident as early as 15 minutes after the onset of ischemia. After 30 minutes of ischemia the decrease in Vmax slowed down, probably due to an "adaptational" decrease of the Km value for Ca-ATPase. This phenomenon may be interpreted as a mechanism by which the enzyme attempts to keep working in a situation when the supply of ATP is insufficient.

Myocardial adenine nucleotide depletion within 1 h of acute coronary artery occlusion

In anaesthetized open-chest casts with occlusion of the left anterior descending coronary artery (LAD), adenine nucleotides and degradation products were studied in small myocardial tissue samples (10-20 mg) with high-pressure liquid chromatography, and tissue blood flow was measured with radioactive microspheres 5, 10, 20, 40, and 60 min after LAD occlusion. There was a rapid and parallel decrease of myocardial ATP and accumulation of adenosine, inosine, hypoxanthine, and xanthine both in epicardial and endocardial half-layers of the ischaemic myocardium within the first 20 min of coronary occlusion. After 40 and 60 min, myocardial ATP content decreased and degradation products accumulated further in the endocardium but stabilized epicardially. Analysis of covariance showed that the slightly higher blood flow in ischaemic epicardial layers, did not explain the transmural difference in ATP content after 40 and 60 min. Adenosine decreased after 40 min of ischaemia in both wall layers reaching negligible amounts after 60 min. It is concluded that breakdown of energy stores is less severe in epicardial than in endocardial wall layers during the first hour after acute coronary occlusion in the cat heart. This transmural difference cannot be explained entirely by less severe epicardial ischaemia. Therefore, transmural heterogeneity in metabolic function during severe ischaemia may also be important.

Myocardial fatty acid oxidation during ischemia and reperfusion

Inhibition of fatty acid oxidation is an early event in myocardial ischemia that most likely contributes to tissue injury by the accumulation of potentially toxic intermediates such as acylCoA and acylcarnitine. After reperfusion both myocardial oxygen consumption and fatty acid oxidation may rapidly recover to preischemic levels, even when contractile function remains depressed. The mechanisms underlying the apparent dissociation between contractile function and oxidative metabolism early during reperfusion are still controversial. In isolated rat hearts subjected to 60 min of no-flow ischemia myocardial oxygen consumption and oxidation of palmitate were lowered during reperfusion by 3 mM of NiCl2 and by 6 microM of ruthenium red. The results provide indirect evidence for the hypothesis that intracellular calcium transport may be involved in the mechanisms responsible for the high oxidative metabolic rate early after reperfusion.