Inosine, not adenosine, initiates endothelial glycocalyx degradation in cardiac ischemia and hypoxia

Ischemia/reperfusion and hypoxia/reoxygenation of the heart both induce shedding of the coronary endothelial glycocalyx. The processes leading from an oxygen deficit to shedding are unknown. An involvement of resident perivascular cardiac mast cells has been proposed. We hypothesized that either adenosine or inosine or both, generated by nucleotide catabolism, attain the concentrations in the interstitial space sufficient to stimulate A3 receptors of mast cells during both myocardial ischemia/reperfusion and hypoxia/reoxygenation. Isolated hearts of guinea pigs were subjected to either normoxic perfusion (hemoglobin-free Krebs-Henseleit buffer equilibrated with 95% oxygen), 20 minutes hypoxic perfusion (buffer equilibrated with 21% oxygen) followed by 20 minutes reoxygenation, or 20 minutes stopped-flow ischemia followed by 20 minutes normoxic reperfusion (n = 7 each). Coronary venous effluent was collected separately from so-called transudate, a mixture of interstitial fluid and lymphatic fluid appearing on the epicardial surface. Adenosine and inosine were determined in both fluid compartments using high-performance liquid chromatography. Damage to the glycocalyx was evident after ischemia/reperfusion and hypoxia/reoxygenation. Adenosine concentrations rose to a level of 1 μM in coronary effluent during hypoxic perfusion, but remained one order of magnitude lower in the interstitial fluid. There was only a small rise in the level during postischemic perfusion. In contrast, inosine peaked at over 10 μM in interstitial fluid during hypoxia and also during reperfusion, while effluent levels remained relatively unchanged at lower levels. We conclude that only inosine attains levels in the interstitial fluid of hypoxic and postischemic hearts that are sufficient to explain the activation of mast cells via stimulation of A3-type receptors.     

Measurement of free radical production by in vivo microdialysis during ischemia/reperfusion injury to skeletal muscle

Microdialysis techniques have been used to detect hydroxyl radical and superoxide release into the interstitial space of anaesthetized rat anterior tibialis muscles during a period of prolonged (4 h) limb ischemia and subsequent reperfusion. Data indicate that reperfusion of the ischemic skeletal muscle was associated with a large increase in hydroxyl radical activity in the interstitial space, which may contribute to the significant oxidation of muscle glutathione, protein thiols, and lipids also seen in this model. No evidence for release of superoxide into the interstitial space was found during reperfusion, although this was observed during electrically stimulated contractile activity of the rat limb muscle. These data imply that therapeutic approaches aimed at reduction of hydroxyl radical generation in the interstitial fluid are more likely to be beneficial in reduction of skeletal muscle reperfusion injury than approaches designed to scavenge superoxide radicals.     

Microdialysis separately monitors myocardial interstitial myoglobin during ischemia and reperfusion

Direct monitoring of myoglobin efflux during ischemia and reperfusion has been limited because of inherent sample collection problems in the ischemic region. Recently, the cardiac dialysis technique has offered a powerful method for monitoring myocardial interstitial levels of low-molecular-weight compounds in the cardiac ischemic region. In the present study, we extended the molecular target to high-molecular-weight compounds by use of microdialysis probes with a high-molecular-mass cutoff and monitored myocardial interstitial myoglobin levels. A dialysis probe was implanted in the left ventricular free wall in anesthetized rabbits. The main coronary artery was occluded for 60 or 120 min. We examined the effects of myocardial ischemia and reperfusion on myocardial interstitial myoglobin levels. Interstitial myoglobin increased within 15 min of ischemia and continued to increase during 120 min of ischemia, whereas blood myoglobin increased at 45 min of ischemia. Lactate and myoglobin in the interstitial space increased during the same period. At 60 min of ischemia, reperfusion markedly accelerated interstitial myoglobin release. The interstitial myoglobin level was fivefold higher at 0-15 min of reperfusion than at 60-75 min of coronary occlusion. The dialysis technique permits earlier detection of myoglobin release and separately monitors myoglobin release during ischemia and reperfusion. Myocardial interstitial myoglobin levels can serve as an index of myocardial injury evoked by ischemia or reperfusion.     

Output, Tissue Levels, and Synthesis of Acetylcholine During and After Transient Forebrain Ischemia in the Rat

Biochemical changes in the rat brain cholinergic system during and after 60 min of ischemia were studied using a four-vessel occlusion model. Extracellular acetylcholine (ACh) concentrations in the unanesthetized rat hippocampus markedly increased during ischemia and reached a peak (about 13.5 times baseline levels) at 5-10 min after the onset of ischemia. At 2-5 h after reperfusion, extracellular ACh concentrations were reduced to 64-72% of the levels of controls. ACh levels in the hippocampus, striatum, and cortex decreased significantly during ischemia and exceeded their control values just after reperfusion. A significant increase in hippocampal ACh level after 2 days of reperfusion and a decrease in [14C]ACh synthesis from [14C]glucose in hippocampal slices excised at 2 days after reperfusion were observed. The extracellular concentrations and tissue levels of choline markedly increased after ischemia. These results show that ACh is markedly released into the extracellular space in the hippocampus during ischemia, and they suggest that ACh synthesis is activated just after reperfusion and that cholinergic activity is reduced after 2-48 h of reperfusion in the hippocampus.     

Ischemia and reperfusion of skeletal muscle lead to the appearance of a stable lipid free radical in the circulation

Both ischemia and reperfusion injury and contractile activity are associated with the generation of reactive oxygen species and free radicals by skeletal muscle. In addition, exercise has been reported to lead to the formation of a circulating free radical species that is detectable in the blood by spin trapping before analysis by electron-spin resonance (ESR) techniques. Previous analysis of the ESR signal indicated that the circulating species is either a carbon- or oxygen-centered lipid-derived free radical. The current data indicate that this species is present in the blood of anesthetized rats after 4-h ischemia and 1 h of reperfusion of a single hindlimb. During 4 h of ischemia, the species was also present in microdialysates from the tibialis anterior muscle but was unchanged in magnitude compared with control tissue. During 1 h of reperfusion, the signal intensity increased by a mean of 420% (P < 0.05, n = 4). Hydroxyl radical activity in the interstitial fluid also significantly increased during ischemia and further increased by a mean of 210% (P < 0.05, n = 4) during reperfusion. No changes in interstitial superoxide levels were seen, but interstitial PGE(2) content also increased during reperfusion. A significant positive correlation was found between the magnitude of the ESR signal and both the hydroxyl radical activity and PGE(2) content of microdialysis fluids. These data support the hypothesis that the circulating free radical species is formed in the interstitial fluid by hydroxyl radical interaction with a lipid that may be released from reperfused tissue with a similar pattern to prostanoids.     

Microdialysis study in vivo of the release of adenine nucleotide degradation products into intercellular space of canine myocardium during regional ischemia and reperfusion

Intercellular concentrations of adenine nucleotide degradation products (ANDP)--adenosine inosine and hypoxanthine--in ischemic and control regions of the canine myocardium were measured by microdialysis technique during 20- and 40-min coronary artery occlusion and reperfusion. In hearts that fibrillated on reperfusion during the ischemic 40-min period catabolism of adenine nucleotides was more intensive, which could be the min cause of the reperfusion ventricular fibrillation. Reperfusion ventricular fibrillation was accompanied by an increase in the intercellular ANDP level in the control region, that indicated the development of the total myocardial ischemia. During the initial period of reperfusion after 20-min, a sharp increase in the interstitial ANDP level was observed in the ischemic region as compared with the end of the ischemia which could be explained as a result of demasking of reperfusion damage in such a case. The 40-min reperfusion induced slow reduction of the intercellular ANDP level in the ischemic region, while the regional blood flow already 5 min after the reperfusion did not differ from the blood flow in the control region. It is supposed that a slow washout of ANDP could be caused by the "no-reflow" phenomenon.     

Noradrenaline dynamics in prolonged ischemia after ischemic preconditioning

AIM OF THE STUDY: To determine the effects of two-staged ischemic preconditioning on myocardial noradrenaline in prolonged ischemia and reperfusion. METHODS: Thirty-two male Wistar rats anesthetised with urethane randomly divided into 2 groups: group 1 (ischemic preconditioning group, n = 16), and group 2 (control, n = 16). Myocardial interstitial noradrenaline levels were measured using a microdialysis technique. Ischemic preconditioning was elicited by two episodes: 5 min of ischemia and 10 min of reperfusion. The intermittent occlusions were followed by prolonged occlusion (60 min) and reperfusion (60 min). RESULTS: An increase in interstitial noradrenaline was observed in 10 min of prolonged ischemia in group 2, and in 20 min in group 1. After 20 min of myocardial ischemia there was a significant difference between groups (p < 0.05) in interstitial noradrenaline levels. In control group, it was 60% higher. In reperfusion, noradrenaline levels decreased markedly in group 1. CONCLUSION: We suggest that ischemic preconditioning by two episodes: 5-min ischemia and 10-min reperfusion prevents excessive noradrenaline interstitial accumulation, perhaps, through protection of physiological uptake I carrier.     

Changes of phospholipid composition and superoxide dismutase activity during global brain ischemia and reperfusion in rats

Alterations in phospholipid content and Cu/Zn superoxide dismutase (SOD) activity were examined in rat brain after 15 min of global ischemia (four-vessel occlusion) followed by 2-, 24- or 48-h reperfusion. Phosphatidylcholine (PC) and phosphatidylethanolamine (PE), the main brain phospholipids, were markedly decreased in ischemic rats and remained decreased during the whole reperfusion period. Concentrations of phosphatidylinositol (PI) and sphingomyelin (SM) were also significantly reduced during ischemia but recovered during reperfusion period. In contrast, phosphatidylserine (PS) and lysophospholipids (LysoPL) were unchanged during ischemia but were elevated after 24 h of reperfusion. Significant reductions in blood plasma phospholipids were also demonstrated. 24-48 h of reperfusion markedly decreased PE, PC and PS contents, while the concentrations were almost unchanged by ischemia alone. Brain SOD activity decreased significantly during ischemia and was recovered to control value already after 2 h of reperfusion. These results suggest that ischemia/reperfusion is accompanied by a significant and selective degradation of brain phospholipids that may be attributable to oxidative stress and activation of phospholipases.     

Left ventricular interstitial 8-hydroxy-deoxyguanosine concentration following myocardial ischemia and reperfusion in anesthetized rats

Summary

The effect of myocardial ischemia and reperfusion on left ventricular interstitial 8-hydroxydeoxyguanosine (8-OH-dG), a possible biomarker for in vivo oxidative deoxyribonucleic acid damage, in anesthetized rats was investigated. A microdialysis probe was implanted. Levels of 8-OH-dG in microdialysates were analyzed via an on-line high performance liquid chromatography system equipped with an electrochemical detector. Myocardial ischemia for 10 or 20 min, induced by clamping of the left anterior descending coronary artery, did not affect 8-OH-dG levels. However, reperfusion following either 10-min or 20-min ischemia significantly increased 8-OH-dG levels in collected microdialysates. Reperfusion-induced increases in 8-OH-dG levels were more prominent in the 20 min ischemia group (as high as 3.5 fold relative to basal levels) than in the 10 min ischemia group as high as 2.0 fold relative to basal levels). In conclusion, we observed that left ventricular interstitial 8-OH-dG concentration increased following myocardial ischemia and reperfusion in anesthetized rats. These results suggest that 8-OH-dG might be a useful biomarker for oxidative damage following myocardial ischemia and reperfusion.     

Oxygen-dependent reperfusion injury in the isolated rat lung.

To further define the relationship between oxygen dependence of lung injury during ischemia and ischemia-reperfusion, we used the isolated, perfused, and ventilated rat lung model, so that oxygenation and perfusion could be separated. During ischemia, lungs were ventilated with various oxygen concentrations and then ventilated with 95% oxygen during the 60-min reperfusion period. Other lungs were ventilated with 0% oxygen (nitrogen) during ischemia, and the reperfusion phase oxygen concentration was varied. Tissue and perfusate lipid peroxidation products (thiobarbituric acid-reactive substances and conjugated dienes), dry-to-wet weight ratio, and lactate dehydrogenase were measured as indexes of lung damage. In addition, electron microscopy of some lungs was performed. Results demonstrate an oxygen dependence of lipid peroxidation in both the ischemic and reperfusion phases, but lipid peroxidation is severalfold greater in the reperfusion than in the ischemic phase. Products of lipid peroxidation closely correlate with indexes of lung injury (dry-to-wet weight ratio, lactate dehydrogenase, and electron microscopy).     

The role of prostaglandins in the antiarrhythmic effect of ischemic preconditioning

The role of prostaglandins in the antiarrhythmic effect of ischemic preconditioning (IP) was investigated in pentobarbital-anesthetized rats. In 5 unpreconditioned control rats, 30 min of occlusion of the left coronary artery elicited ventricular tachycardia (VT) and fibrillation (VF), with an average duration of VT and VF of 51 +/- 6 and 43 +/- 4 s, respectively. Frequent ventricular premature beats (VPBs; average 1,249 +/- 145) were also documented in these animals. Thirty minutes of reperfusion after the prolonged coronary occlusion in these animals caused more severe arrhythmias, including irreversible VF. In animals pretreated with IP (n = 5), which was achieved by 3 cycles of 3 min of occlusion followed by 5 min of reperfusion, 30 min of coronary artery occlusion caused neither VT nor VF, but occasional VPBs (average 2 +/- 1, p < 0.001 vs. control). Only occasional VPBs were observed during 30 min of reperfusion in this group. In animals pretreated with indomethacin (1 mg/kg i.v., n = 5) followed by IP, prolonged ischemia and reperfusion led to frequent VPBs but no VT or VF. The average number of VPBs during ischemia and reperfusion in this indomethacin-treated group was less than that of the controls but greater than the IP-only group (p < 0.01). In conclusion, prostaglandins appear to play a role in the protective effect of IP against VPBs during acute ischemia and reperfusion.     

Complement-dependent NADPH oxidase enzyme activation in renal ischemia/reperfusion injury

NADPH oxidase plays a central role in mediating oxidative stress during heart, liver, and lung ischemia/reperfusion injury, but limited information is available about NADPH oxidase in renal ischemia/reperfusion injury. Our aim was to investigate the activation of NADPH oxidase in a swine model of renal ischemia/reperfusion damage. We induced renal ischemia/reperfusion in 10 pigs, treating 5 of them with human recombinant C1 inhibitor, and we collected kidney biopsies before ischemia and 15, 30, and 60 min after reperfusion. Ischemia/reperfusion induced a significant increase in NADPH oxidase 4 (NOX-4) expression at the tubular level, an upregulation of NOX-2 expression in infiltrating monocytes and myeloid dendritic cells, and 8-oxo-7,8-dihydro-2′-deoxyguanosine synthesis along with a marked upregulation of NADPH-dependent superoxide generation. This burden of oxidative stress was associated with an increase in tubular and interstitial expression of the myofibroblast marker α-smooth muscle actin (α-SMA). Interestingly, NOX-4 and NOX-2 expression and the overall NADPH oxidase activity as well as α-SMA expression and 8-oxo-7,8-dihydro-2′-deoxyguanosine synthesis were strongly reduced in C1-inhibitor-treated animals. In vitro, when we incubated tubular cells with the anaphylotoxin C3a, we observed an enhanced NADPH oxidase activity and α-SMA protein expression, which were both abolished by NOX-4 silencing. In conclusion, our findings suggest that NADPH oxidase is activated during ischemia/reperfusion in a complement-dependent manner and may play a potential role in the pathogenesis of progressive renal damage in this setting.     

Studies on the effects of lactate transport inhibition, pyruvate, glucose and glutamine on amino acid, lactate and glucose release from the ischemic rat cerebral cortex

A rat four vessel occlusion model was utilized to examine the effects of ischemia/reperfusion on cortical window superfusate levels of amino acids, glucose, and lactate. Superfusate aspartate, glutamate, phosphoethanolamine, taurine, and GABA were significantly elevated by cerebral ischemia, then declined during reperfusion. Other amino acids were affected to a lesser degree. Superfusate lactate rose slightly during the initial ischemic period, declined during continued cerebral ischemia and then was greatly elevated during reperfusion. Superfusate glucose levels declined to near zero levels during ischemia and then rebounded beyond basal levels during the reperfusion period. Inhibition of neuronal lactate uptake with alpha-cyano-4-hydroxycinnamate dramatically elevated superfusate lactate levels, enhanced the ischemia/reperfusion evoked release of aspartate but reduced glutamine levels. Topical application of an alternative metabolic fuel, glutamine, had a dose dependent effect. Glutamine (1 mM) elevated basal superfusate glucose levels, diminished the decline in glucose during ischemia, and accelerated its recovery during reperfusion. Lactate levels were elevated during ischemia and reperfusion. These effects were not evident at 5 mM glutamine. At both concentrations, glutamine significantly elevated the superfusate levels of glutamate. Topical application of sodium pyruvate (20 mM) significantly attenuated the decline in superfusate glucose during ischemia and enhanced the levels of both glucose and lactate during reperfusion. However, it had little effect on the ischemia-evoked accumulation of amino acids. Topical application of glucose (450 mg/dL) significantly elevated basal superfusate levels of lactate, which continued to be elevated during both ischemia and reperfusion. The ischemia-evoked accumulations of aspartate, glutamate, taurine and GABA were all significantly depressed by glucose, while phosphoethanolamine levels were elevated. These results support the role of lactate in neuronal metabolism during ischemia/reperfusion. Both glucose and glutamine were also used as energy substrates. In contrast, sodium pyruvate does not appear to be as effectively utilized by the ischemic/reperfused rat brain since it did not reduce ischemia-evoked amino acid efflux.     

Effect of ozone treatment on reactive oxygen species and adenosine production during hepatic ischemia-reperfusion

This study investigates whether ozone could confer protection from hepatic ischemia reperfusion by modifying the accumulation of adenosine and xanthine during ischemia. A significant increase in both adenosine and xanthine accumulation was observed as a consequence of ATP degradation during hepatic ischemia. Adenosine exerts a protective effect on hepatic ischemia reperfusion injury since the elimination of endogenous adenosine accumulation with adenosine deaminase increased the hepatic injury associated with this process. On the other hand, the high xanthine levels observed after ischemia could exert deleterious effects during reperfusion due to reactive oxygen species generation from xanthine oxidase. The administration of allopurinol, an inhibitor of xanthine oxidase, attenuated the increase in reactive oxygen species and transaminase levels observed after hepatic reperfusion. Ozone treatment in liver maintained adenosine levels similar to those found after ischemia but led to a marked reduction in xanthine accumulation. In order to evaluate the role of both adenosine and xanthine, we tried to modify the protection confered by ozone, by modifying the concentrations of adenosine and xanthine. The metabolization of endogenous adenosine after ischemia abolished the protective effect conferred by ozone. When xanthine was administered previous to ozone treatment, the protection conferred by adenosine disappeared, showing both postischemic reactive oxygen species and transaminase levels similar to those found after hepatic ischemia reperfusion. Ozone would confer protection against the hepatic ischemia reperfusion injury by the accumulation of adenosine that in turns benefits the liver and by blocking the xanthine/xanthine oxidase pathway for reactive oxygen species generation.     

Effect of ozone treatment on reactive oxygen species and adenosine production during hepatic ischemia-reperfusion

This study investigates whether ozone could confer protection from hepatic ischemia reperfusion by modifying the accumulation of adenosine and xanthine during ischemia. A significant increase in both adenosine and xanthine accumulation was observed as a consequence of ATP degradation during hepatic ischemia. Adenosine exerts a protective effect on hepatic ischemia reperfusion injury since the elimination of endogenous adenosine accumulation with adenosine deaminase increased the hepatic injury associated with this process. On the other hand, the high xanthine levels observed after ischemia could exert deleterious effects during reperfusion due to reactive oxygen species generation from xanthine oxidase. The administration of allopurinol, an inhibitor of xanthine oxidase, attenuated the increase in reactive oxygen species and transaminase levels observed after hepatic reperfusion. Ozone treatment in liver maintained adenosine levels similar to those found after ischemia but led to a marked reduction in xanthine accumulation. In order to evaluate the role of both adenosine and xanthine, we tried to modify the protection confered by ozone, by modifying the concentrations of adenosine and xanthine. The metabolization of endogenous adenosine after ischemia abolished the protective effect conferred by ozone. When xanthine was administered previous to ozone treatment, the protection conferred by adenosine disappeared, showing both postischemic reactive oxygen species and transaminase levels similar to those found after hepatic ischemia reperfusion. Ozone would confer protection against the hepatic ischemia reperfusion injury by the accumulation of adenosine that in turns benefits the liver and by blocking the xanthine/xanthine oxidase pathway for reactive oxygen species generation.     

Changes in Extracellular Concentrations of Glutamate, Aspartate, Glycine, Dopamine, Serotonin, and Dopamine Metabolites After Transient Global Ischemia in the Rabbit Brain

Although considerable evidence supports a role for excitatory amino acids in the pathogenesis of ischemic neuronal injury, few in vivo studies have examined the effect of increasing durations of ischemia on the extracellular concentrations of these agents. Recently, other neurotransmitters (e.g., glycine and dopamine) have been implicated in the mechanism of ischemic neuronal injury. Accordingly, this study was undertaken to examine the patterns of changes of extracellular glutamate, aspartate, glycine concentrations in the hippocampus, and dopamine, serotonin, and dopamine metabolites in the caudate nucleus with varying durations (5, 10, or 15 minutes) of transient global cerebral ischemia as evidence to support their pathogenetic roles. Microdialysis was used to sample the brain's extracellular space before, during, and after the ischemic period. Glutamate and aspartate concentrations in the dialysate increased from baseline by 1-, 5-, and 13-fold and by 4-, 9-, and 31-fold, respectively, for the three ischemic durations. The concentrations returned to baseline rapidly after reperfusion. The peak concentrations of glutamate and aspartate were significantly higher with increasing ischemic duration. Dopamine concentrations increased by approximately 700-fold in response to all three ischemic durations and returned to baseline within 10 min of reperfusion. Glycine, in contrast, increased during ischemia by a mean of 4-fold, but remained elevated throughout the 80-min period of reperfusion. The final concentrations of glycine were significantly higher than baseline levels (p = 0.0002, Mann-Whitney test). That glutamate and aspartate concentrations in the hippocampus co-vary with the duration of global ischemia is taken as supportive evidence of their pathogenetic role in ischemic neuronal injury.(ABSTRACT TRUNCATED AT 250 WORDS)     

Placental growth factor signaling regulates isoform splicing of vascular endothelial growth factor A in the control of lung cancer cell metastasis

The omega-3 fatty acid, alpha linolenic acid (ALA) found in plant-derived foods induces significant cardiovascular benefits when ingested. ALA may be cardioprotective during ischemia; however, the mechanism(s) responsible for this effect is unknown. Isolated adult rat cardiomyocytes were exposed to medium containing ALA for 24 h and then exposed to non-ischemic (control), simulated ischemia (ISCH), or simulated ischemia/reperfusion (IR) conditions. Cardiomyocyte phospholipids were extracted and analyzed by an HPLC/electrospray ionization tandem mass spectrometry system. Pre-treatment of cells with ALA resulted in a significant incorporation of ALA within cardiomyocyte phosphatidylcholine. Cell death, DNA fragmentation and caspase-3 activity increased during ischemia and ischemia/reperfusion. Two pro-apoptotic oxidized phosphatidylcholine (OxPC) species, 1-palmitoyl-2-(5′-oxo-valeroyl)-sn-glycero-3-phosphocholine (POVPC), and 1-palmitoyl-2-glutaroyl-sn-glycero-3-phosphocholine (PGPC) were significantly increased during both ischemia and ischemia/reperfusion. Pre-treatment of the cells with ALA resulted in a significant reduction in cell death during ischemia and ischemia/reperfusion challenge. Apoptosis was also inhibited during ischemia and ischemia/reperfusion as shown by reduced DNA fragmentation and decreased caspase activation. ALA pre-treatment significantly decreased the production of POVPC and PGPC during ischemia and ischemia/reperfusion. ALA pre-treatment also significantly increased in resting Ca²⁺ during ischemia or ischemia/reperfusion but did not improve Ca²⁺ transients. ALA protects the cardiomyocyte from apoptotic cell death during simulated ISCH and IR by inhibiting the production of specific pro-apoptotic OxPC species. OxPCs represent a viable interventional target to protect the heart during ischemic challenge.     

Glucagon-like peptide-1 (7-36) amide prevents the accumulation of pyruvate and lactate in the ischemic and non-ischemic porcine myocardium

Glucagon-like peptide-1 (7-36) amide (GLP-1) has been studied as a treatment option in diabetic patients. We investigated the effect of recombinant GLP-1 infusion on hemodynamic parameters, myocardial metabolism, and infarct size during normoxic conditions as well as during ischemia and reperfusion using an open-chest porcine heart model. In the presence of rGLP-1, interstitial levels of pyruvate and lactate decreased during ischemia and reperfusion both in ischemic and non-ischemic tissue. Moreover, rGLP-1 infusion resulted in increased plasma insulin levels and decreased blood glucose levels. Neither hemodynamic variables nor the consequent infarct size were influenced by rGLP-1 infusion. We conclude that rGLP-1 altered myocardial glucose utilization during ischemia and reperfusion. It did not exert any untoward hemodynamic effects.     

Cardiac glucose uptake and suppressed expression/translocation of myocardium glucose transport-4 in dogs undergoing ischemia-reperfusion

Impaired glucose metabolism is implicated in cardiac failure during ischemia-reperfusion. This study examined cardiac glucose uptake and expression of glucose transport-4 (GLUT-4) in dogs undergoing ischemia-reperfusion. Cardiac ischemia was induced by cardiopulmonary bypass for 30 min or 120 min in dogs. Plasma insulin and glucose concentrations were measured at pre-bypass (control), and aortic cross-clamp off (ischemia-reperfusion) at 15, 45, and 75 min. At the same time, the left ventricle biopsies were taken for GLUT-4 immunohistochemistry and glycogen content analysis. In dogs receiving 120-min ischemia, coronary arterial and venous glucose concentrations were increased, but the net glucose uptake in ischemia-reperfusion heart were significantly decreased from 25% (control) to zero at 15 and 45 min of reperfusion, and recovered to only 7% after 75 min reperfusion. Myocardium glycogen contents were decreased by 65%. Plasma insulin levels and Insulin Resistant Index were markedly increased in dogs undergoing 120-min ischemia and reperfusion. These changes were relatively mild and reversible in dogs receiving only 30-min ischemia followed by reperfusion. Expression of total GLUT-4 in myocardium was decreased 40% and translocation of GLUT-4 from cytoplasm to surface membrane was decreased 90% in dogs receiving 120-min ischemia followed by 15-min reperfusion. Suppressed translocation of GLUT-4 was also evident in dogs receiving 30-min ischemia, but to a lesser extent. Reduced myocardium glucose uptake, utilization, and glycogen content are clearly associated with ischemia-reperfusion heart injury. This appears to be due, at least in part, to suppressed expression and translocation of myocardium GLUT-4.     

Effects of Mild Hypothermia on the Release of Regional Glutamate and Glycine During Extended Transient Focal Cerebral Ischemia in Rats

The present study is to determine the effect of mild hypothermia (MHT) on the release of glutamate and glycine in rats subjected to middle cerebral artery occlusion and reperfusion. The relationship between amino acid efflux and brain infarct volume was compared in different periods during MHT. Reversible middle cerebral artery occlusion was performed in Sprague-Dawley rats using a suture model. The rats were divided into four groups including (1) MHT during ischemia (MHTi), (2) MHT during reperfusion (MHTr), (3) MHT during ischemia and reperfusion (MHTi + r), and (4) a normothermic group (NT). Extracellular concentrations of glutamate and glycine in the cortex and striatum were monitored using in vivo microdialysis and analyzed using high-performance liquid chromatography. Morphometric measurements for infarct volume were performed using 2,3,5-triphenyltetrazolium chloride staining. The increase of glutamate and glycine in the ischemic cortex of the MHTi and MHTi + r rats during ischemic and reperfusion periods was significantly less than that of the NT rats (p < 0.05). However, there was no statistical difference among these groups in the peak of glutamate and glycine release in the striatum. Infarct volume paralleled the release of glutamate and glycine. The protective effect of MHTi and MHTi + r in reducing ischemia and reperfusion brain injury may be due to the attenuation of both glutamate and glycine release during ischemia and reperfusion.