Preconditioning protects the severely atherosclerotic mouse heart

BACKGROUND: Coronary atherosclerosis has profound effects on vascular and myocardial biology, and it has been speculated that the atherosclerotic heart does not benefit from ischemic preconditioning. METHODS: To investigate if atherosclerosis would influence the preconditioning response, Apolipoprotein E/low density lipoprotein (LDL) receptor double knockout mice (ApoE/LDLr-/-) were fed an atherogenic diet (21% fat, 0.15% cholesterol) for 6 to 8 months. At that time, extensive atherosclerotic lesions throughout the coronary tree were seen in transverse sections stained with Oil Red-O. Hearts of ApoE/LDLr-/- mice were Langendorff-perfused with 40 minutes of global ischemia and 60 minutes reperfusion, and compared with C57BL/6 controls. Preconditioning with two episodes of 2 minutes of ischemia and 5 minutes reperfusion, or exposing the mice to a hyperoxic environment (O2 > 98%) for 60 minutes before heart perfusion, was performed. RESULTS: Hearts of mice with coronary atherosclerosis had worse postischemic function, and increased infarct size and troponin T release compared to hearts of C57BL/6 mice. Ischemic preconditioning improved postischemic ventricular function, and reduced myocardial infarct size and troponin T release in both normal and ApoE/LDLr-/- mice. The effects were most pronounced in ApoE/LDLr-/- hearts. Exposure to hyperoxia exerted a similar protection of function and cell viability of ApoE/LDLr-/- mice hearts. CONCLUSIONS: These findings suggest that the severely atherosclerotic heart may be protected by preconditioning induced by ischemia or hyperoxia.     

Lipopolysaccharide pretreatment attenuates myocardial infarct size: A possible mechanism involving heat shock protein 70-inhibitory kappaBalpha complex and attenuation of nuclear factor kappaB

OBJECTIVE: Lipopolysaccharide pretreatment is known to reduce myocardial infarct size, but the mechanism has not been elucidated. We hypothesized that heat shock protein 70, induced by lipopolysaccharide pretreatment, formed complexes with inhibitory kappaBalpha, thereby inhibiting degradation and attenuating activation of nuclear factor kappaB and cellular injury in rat myocardium. METHODS: Fifteen Sprague-Dawley rats were given saline solution (control group) or lipopolysaccharide. After 48 hours, 5 hearts in each group were excised without ischemia for examination of heat shock protein 70 and inhibitory kappaBalpha levels and detection of heat shock protein 70-inhibitory kappaBalpha complexes. Myocardium from the remaining 10 rats in each group was exposed to 30 minutes of ischemia and 30 minutes of reperfusion (n = 5) to evaluate nuclear factor kappaB activity or to 24 hours of reperfusion (n = 5) to evaluate infarct size. RESULTS: Infarct size was reduced in the lipopolysaccharide group (P <.05). Nuclear factor kappaB was activated in the control ischemia group and attenuated in the lipopolysaccharide group (P <.05). Heat shock protein 70 levels were increased in the lipopolysaccharide group (P <.05), but inhibitory kappaBalpha levels were similar in both groups. Heat shock protein 70-inhibitory kappaBalpha complexes were detected only in the lipopolysaccharide group. Colocalization of the 2 proteins was observed in the lipopolysaccharide group. CONCLUSIONS: Heat shock protein 70, induced by lipopolysaccharide pretreatment, forms complexes with inhibitory kappaBalpha and attenuates activation of nuclear factor kappaB and myocardial infarct size. Our results suggest that attenuation of nuclear factor kappaB through a mechanism forming heat shock protein 70-inhibitory kappaBalpha complexes might protect the myocardium from ischemia-reperfusion injury.     

抑制核转录因子减轻心肌缺血再灌注损伤

目的　观察核转录因子(NF-κB)激活抑制剂吡咯二硫氨基甲酸酯(PDTC)对心肌缺血和再灌注损伤的影响。方法　结扎和开放新西兰白兔心脏左冠状动脉前降支,造成局部心肌缺血45min和再灌注120min。缺血前静脉注射PDTC(15mg/kg),对照组给予生理盐水。将压力传感探头包埋于缺血区心外膜下,测定局部心肌的缩短度;再灌注末用氯化三苯四唑啉法计算心肌缺血区梗死面积,并做心肌病理观察和NF-κB免疫电泳活性测定。结果　与对照组相比,实验组在再灌注30min以后心肌缩短度显著改善(P＜0.05);缺血心肌梗死面积显著减小［(19.3±5.2)%对(54.7±6.5)%,P＜0.05］;心肌血管内皮白细胞粘附和浸润减少,结构损害较轻;NF-κB活性明显减弱。结论　核转录因子激活抑制剂PDTC可减轻白细胞介导的心肌缺血再灌注损伤。     

Adenosine-enhanced ischemic preconditioning modulates necrosis and apoptosis: effects of stunning and ischemia-reperfusion

BACKGROUND: Adenosine-enhanced ischemic preconditioning extends the protection of ischemic preconditioning by both significantly decreasing infarct size and significantly enhancing postischemic functional recovery. METHODS: The effects of adenosine-enhanced ischemic preconditioning on necrosis and apoptosis were investigated in the sheep heart using models of stunning (15 minutes regional ischemia, 120 minutes reperfusion) and ischemia-reperfusion (30 and 60 minutes regional ischemia, 120 minutes reperfusion). Ischemic preconditioned hearts received 5 minutes regional ischemia, 5 minutes reperfusion before ischemia. Adenosine-enhanced ischemic preconditioned hearts received a 10 mmol/L adenosine bolus (10 mL) through the left atrium coincident with ischemic preconditioning. Adenosine hearts received a 10 mmol/L bolus (10 mL) of adenosine. Regional ischemic hearts received no pretreatment. RESULTS: Minimal apoptosis (< 45 per 3,000 myocytes) was observed in the stunning models but was significantly increased with ischemia-reperfusion in regional ischemic hearts after 30 minutes (p < 0.05 versus ischemic preconditioning, adenosine, or adenosine-enhanced ischemic preconditioning) and in adenosine and ischemic preconditioned hearts after 60 minutes ischemia (p < 0.05 versus adenosine-enhanced ischemic preconditioning). DNA laddering was apparent after 60 minutes ischemia in regional ischemia, adenosine, and ischemic preconditioning but not in adenosine-enhanced ischemic preconditioned hearts. CONCLUSIONS: Adenosine-enhanced ischemic preconditioning significantly ameliorates necrosis and apoptosis in the regional ischemic blood-perfused heart.     

Beneficial effect of tetrahydrobiopterin on ischemia-reperfusion injury in isolated perfused rat hearts

OBJECTIVE: It has recently been proposed that nitric oxide synthase, in the presence of suboptimal levels of tetrahydrobiopterin, an essential cofactor of this enzyme, might favor increased production of oxygen radicals. The aim of this study was to clarify whether supplement with tetrahydrobiopterin would exert a cardioprotective effect against ischemia-reperfusion injury. METHODS: Isolated perfused rat hearts were subjected to 30 minutes of global ischemia and 30 minutes of reperfusion at 37 degrees C. Hearts were treated with tetrahydrobiopterin or vehicle for 5 minutes just before ischemia and during the first 5 minutes of the reperfusion period. Effects of tetrahydrobiopterin on left ventricular function, myocardial contents of lipid peroxidation and high-energy phosphates, and levels of lactate dehydrogenase and nitrite plus nitrate in perfusate during ischemia and after reperfusion were estimated and further compared with those of superoxide dismutase plus catalase or L-ascorbic acid. RESULTS: Tetrahydrobiopterin and superoxide dismutase plus catalase both improved contractile and metabolic abnormalities in reperfused hearts. On the other hand, L-ascorbic acid at a dose having an equipotent radical scavenging activity with tetrahydrobiopterin did not significantly affect the postischemic changes. Although tetrahydrobiopterin and superoxide dismutase plus catalase significantly alleviated ischemic contracture during ischemia, diminished perfusate levels of nitrite plus nitrate after reperfusion were restored only with tetrahydrobiopterin. CONCLUSION: Results demonstrated that tetrahydrobiopterin lessens ischemia-reperfusion injury in isolated perfused rat hearts, probably independent of its intrinsic radical scavenging action. The cardioprotective effect of tetrahydrobiopterin implies that tetrahydrobiopterin could be a novel and effective therapeutic option in the treatment of ischemia-reperfusion injury.     

Na(+)/H(+) exchanger inhibitor HOE642 offers myoprotection in senescent myocardium independent of ischemic preconditioning mechanisms

BACKGROUND: Inhibition of Na(+)/H(+) exchange has been shown to provide functional protection during ischemia and reperfusion in mature heart. This study was undertaken to elucidate the effect of Na(+)/H(+) exchange inhibitor HOE642 in the aged rabbit heart. METHODS: Isolated rabbit hearts were subjected to 1 h of left descending coronary artery (LAD) ischemia and 1 h of reperfusion. To determine the effects of HOE642 on ischemia/reperfusion injury, seven aged or mature hearts received the Na(+)/H(+) exchange inhibitor HOE642 (1 microM) for 15 min before the ischemia and for 30 min after reperfusion. Seven aged (more than 135 weeks) or mature (15-20 weeks) rabbit hearts served as a control (untreated) with no interventions. Left ventricular pressures, monophasic action potentials and coronary flows were measured throughout the experiment and infarct size was detected at the end of experiment. RESULTS: (1) In the mature hearts, HOE642 improved postischemic functional recovery (63.1 +/- 5.0% vs. 84.4 +/- 5.4%, mature untreated vs. mature HOE, p < 0.05) and reduced infarct size as compared to untreated hearts (42.0 +/- 2.5% vs. 24.8 +/- 2.3%, mature untreated vs. mature HOE, p < 0.05). (2) Although infarct size in aged untreated hearts was significantly decreased as compared to mature untreated hearts (42.0 +/- 2.5% vs. 19.3 +/- 1.6%, mature untreated vs. aged untreated, p < 0.05), there are no significant differences regarding postischemic functional recovery between mature and aged untreated hearts (63.1 +/- 5.0% vs. 59.5 +/- 5.9%, mature untreated vs. aged untreated, p = n.s.). (3) In the aged hearts, HOE642 improved postischemic functional recovery as compared to untreated hearts (59.5 +/- 5.9% vs. 85.9 +/- 8.1%, aged untreated vs. aged HOE, p < 0.05). CONCLUSION: Na(+)/H(+) exchange inhibitor HOE642 is effective against ischemia-reperfusion injury in senescent as well as mature hearts.     

Promoting angiogenesis protects severely hypertrophied hearts from ischemic injury

BACKGROUND: Myocardial hypertrophy is associated with progressive contractile dysfunction, increased vulnerability to ischemia-reperfusion injury, and is, therefore, a risk factor in cardiac surgery. During the progression of hypertrophy, a mismatch develops between the number of capillaries and cardiomyocytes per unit area, suggesting an increase in diffusion distance and the potential for limited supply of oxygen and nutrients. We hypothesized that promoting angiogenesis in hypertrophied hearts increases microvascular density, thereby improves tissue perfusion and substrate availability, maintains myocardial function, and improves postischemic recovery. METHODS: Left ventricular hypertrophy was created in 10-day-old rabbits by aortic banding and progression was monitored by echocardiography. At 4 weeks (compensated hypertrophy), 2 microg of vascular endothelial growth factor (VEGF) or placebo was administered intrapericardially. After 2 weeks, microvascular density, coronary flow (CF), and glucose uptake (GU) were measured. Tolerance to ischemia was determined by cardiac function measurements before and after ischemia-reperfusion using an isolated heart preparation. RESULTS: Microvascular density increased significantly following VEGF treatment (1.43 +/- 0.08/nuclei/field vs 1.04 +/- 0.06/nuclei/field untreated hypertrophy). Concomitantly, there was an increase in CF (7 +/- 0.5 vs 5 +/- 0.4 mL/min/g) and GU (1.24 +/- 0.2 vs 0.69 +/- 0.2 micromoles/g/30 minutes; p 相似文献   

Effects of tramadol on myocardial ischemia-reperfusion injury

OBJECTIVES: The aim of the present study was to evaluate the effect of tramadol on isolated rat hearts subjected to global ischemia-reperfusion injury. DESIGN: Langerdorff perfused isolated rat hearts were subjected to 60 min of global ischemia following 60 min of reperfusion. In group I and III hearts were received tramadol before the onset of ischemia. Following the ischemic period, group II and III hearts were received tramadol infusion. Group I and IV hearts were subjected to saline at the same time point. The myocardial postischemic recovery was compared using hemodynamic, coronary flow, biochemical parameters from coronary effluent, and oxidative stress markers from heart tissue homogenates. RESULTS: There were significant differences between tramadol and saline used groups in hemodynamic parameters. GPx values of groups I and III were significantly lower than group IV (p<0.05). SOD values of groups I, II and III were higher than group IV (p<0.05). LDH values of groups I and II were significantly lower than groups III and IV (p<0.05). CONCLUSION: Tramadol provides a cardioprotective effect against myocardial ischemia-reperfusion in isolated rat heart.     

Postnatal increase in insulin-sensitive glucose transporter expression is associated with improved recovery of postischemic myocardial function

OBJECTIVE: Glucose is an important substrate for energy production in the developing heart. Increased glucose uptake rate and metabolism during ischemia and reperfusion are closely linked to postischemic myocardial recovery. The initial rate-limiting step for glycolysis is the transport of glucose across the plasma membrane by glucose transporters (GLUT-1 and GLUT-4). We hypothesized that changes in GLUT-1 and GLUT-4 expression in developing hearts lead to age-dependent adaptive changes in glucose uptake capacity and influence tolerance to ischemia. METHODS: Western-immunoblotting was performed to determine GLUT-1 and GLUT-4 expression in myocardial tissue from 1, 2, and 3-week-old and adult rabbits. Glucose uptake rate was measured with (31)P-nuclear magnetic resonance spectroscopy using 2-deoxyglucose as substrate in isolated perfused hearts. Hearts from same age rabbits were perfused in the Langendorff mode with crystalloid buffer or buffer plus a GLUT-4 specific antibody in order to determine GLUT-4 mediated effects on myocardial protection. The hearts were subjected to 30 minutes of normothermic ischemia followed by reperfusion. Cardiac contractile function measurements were obtained pre- and postischemia. Tissue lactate accumulation was measured in all groups at end-ischemia CONCLUSIONS: Insulin-regulated glucose transporter (GLUT-4) expression in the heart increased gradually after birth reaching nearly adult levels by 3 weeks of age. Corresponding with the higher amount of GLUT-4 protein, improved recovery of postischemic contractile function was seen in older hearts in association with increased anaerobic glycolytic capacity. Interventions to accelerate postnatal GLUT-4 expression may improve ischemic tolerance in the neonatal heart.     

The effects of propofol on cardiac function after 4 hours of cold cardioplegia and reperfusion

OBJECTIVE: To examine whether propofol protects against postischemic myocardial dysfunction and apoptosis during reperfusion after prolonged cold ischemia in isolated rat hearts. DESIGN: A prospective, randomized, controlled study. SETTING: A university laboratory. PARTICIPANTS: Animals. INTERVENTIONS: The isolated hearts of 40 Sprague-Dawley male rats were perfused with modified Krebs-Hennseleit solution for 15 minutes for a stabilization period and 15 minutes for a perfusion period and then underwent 4 hours of global cold ischemia followed by 60 minutes of reperfusion. Four groups were studied (n = 10 for each group). Ten hearts served as an untreated control group. Propofol (2 micromol/L) treatment was performed only before ischemia in the PRE group, only during reperfusion in the POST group, and both before and after ischemia in the ALL group. MEASUREMENTS AND MAIN RESULTS: Infusion of propofol during reperfusion improved recovery of left ventricular-developed pressure (LVDP) from 61.2% +/- 8.5% (control) to 86.3% +/- 12.1% (POST) and 74.9% +/- 13.2% (ALL, both p < 0.05), whereas preischemic infusion of propofol (64.3% +/- 9.7%, PRE) did not improve recovery of LVDP. Infusion of propofol during reperfusion significantly reduced the number of apoptotic cells and led to a smaller infarct size than control and PRE groups (p < 0.05, respectively). CONCLUSIONS: Propofol infusion during the reperfusion period produced a cardioprotective effect and inhibited apoptosis of cardiomyocytes in the ischemia-reperfusion model, with prolonged cold ischemia, in isolated rat hearts.     

Role of ceramide in ischemic preconditioning

BACKGROUND: A recent study showed increased myocardial content of ceramide and sphingosine during preconditioning (PC). Because sphingosine-1-phosphate, a metabolite of ceramide, may function as an antiapoptotic factor, we hypothesized the increased ceramide during PC may be heart's effort to harness its own protection. STUDY DESIGN: The isolated hearts were divided into five groups: 1) perfused for 3 hours 45 minutes with KHB buffer (control); 2) perfused with buffer for 45 minutes followed by 30 minutes of ischemia and 2 hours of reperfusion; 3) perfused for 15 minutes with desipramine followed by 30 minutes of perfusion with buffer, 30 minutes of ischemia, and 2 hours of reperfusion; 4) preconditioned followed by 30 minutes of ischemia and 2 hours of reperfusion; and 5) the same as 4), but preperfused for 15 minutes with desipramine. Myocardial preservation was assessed by examining left ventricular function, infarct size, and cardiomyocyte apoptosis. RESULTS: Ischemia/reperfusion-mediated cardiac dysfunction was partially restored with desipramine. PC improved postischemic ventricular recovery and reduced myocardial infarct size and cardiomyocyte apoptosis. The cardioprotective abilities of PC were abolished with desipramine, which also downregulated a PC-mediated increase in antiapoptotic protein Bcl-2. The apparent paradoxical results of desipramine can be explained by the increase in proapoptotic ceramide content in the ischemic reperfused heart that was blocked with desipramine and an increase in antiapoptotic sphingosine-1-p content in the preconditioned heart that was inhibited with desipramine. CONCLUSIONS: The results suggested for the first time that sphingolipid can induce the expression of Bcl-2 warranting its clinical use as a pharmacologic PC agent.     

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

Background. Recently we have reported a novel myoprotective protocol “adenosine-enhanced ischemic preconditioning” (APC), which extends and amends the protection afforded by ischemic preconditioning (IPC) by both reducing myocardial infarct size and enhancing postischemic functional recovery in the mature rabbit heart. However, the efficacy of APC in the senescent myocardium was unknown.

Methods. The efficacy of APC was investigated in senescent rabbit hearts and compared with magnesium-supplemented potassium cardioplegia (K/Mg) and IPC. Global ischemia (GI) hearts were subjected to 30 minutes of global ischemia and 120 minutes of reperfusion. Ischemic preconditioning hearts received 5 minutes of global ischemia and 5 minutes of reperfusion before global ischemia. Magnesium-supplemented potassium cardioplegia hearts received cardioplegia just before global ischemia. Adenosine-enhanced ischemic preconditioning hearts received a bolus injection of adenosine in concert with IPC. To separate the effects of adenosine from that of APC, a control group (ADO) received a bolus injection of adenosine 10 minutes before global ischemia.

Results. Infarct size was significantly decreased to 18.9% ± 2.7% with IPC (p < 0.05 versus GI); 17.0% ± 1.0% with ADO (p < 0.05 versus GI); 7.7% ± 1.3% with K/Mg (p < 0.05 versus GI, IPC, and ADO); and 2.1% ± 0.6% with APC (p < 0.05 versus GI, IPC, ADO, and K/Mg; not significant versus control). Only APC and K/Mg significantly enhanced postischemic functional recovery (not significant versus control).

Conclusions. Adenosine-enhanced ischemic preconditioning provides similar protection to K/Mg cardioplegia, significantly enhancing postischemic functional recovery and decreasing infarct size in the senescent myocardium.     

Adenosine-enhanced ischemic preconditioning provides myocardial protection equal to that of cold blood cardioplegia

BACKGROUND: We recently described a novel myoprotective protocol-adenosine-enhanced ischemic preconditioning (APC)-that extends the protection of ischemic preconditioning (IPC) by both reducing myocardial infarct size and enhancing postischemic functional recovery in the isolated perfused heart. In the present report the efficacy of APC in the blood-perfused heart was investigated and compared with that of cold blood cardioplegia (CBC). METHODS: Cardiopulmonary bypass was instituted in 21 sheep hearts. The APC hearts (n = 6) received a bolus injection of adenosine through the aortic root at the immediate start of IPC (5 minutes of zero-flow global ischemia, followed by 5 minutes of reperfusion) before 30 minutes of global ischemia and 120 minutes of reperfusion. Nine other hearts received CBC. A control group (n = 6) received IPC only. RESULTS: Infarct size was significantly decreased (p<0.01) in the APC (3.0%+/-0.8%) and CBC (2.6%+/-0.2%) hearts compared with the IPC hearts (16.3%+/-1.6%). The preload recruitable stroke work relation, mean arterial pressure, and the time constant of pressure decay (tau) were significantly preserved (p<0.05) in APC and CBC hearts compared with IPC hearts. No significant differences were observed between APC and CBC hearts. CONCLUSIONS: Use of APC is as effective as CBC in significantly decreasing infarct size and enhancing post-ischemic functional recovery.     

Fucoidin reduces coronary microvascular leukocyte accumulation early in reperfusion

Background. Leukocytes rapidly accumulate in the heart early in reperfusion after ischemia, contributing to reperfusion injury. The purpose of this study was to determine whether treatment with the selectin blocker fucoidin (FCN) would attenuate early leukocyte retention in coronary venules and capillaries during low flow reperfusion.

Methods. Isolated rat hearts subjected to 30 minutes of 37°C, no-flow ischemia were initially reperfused with blood containing labeled leukocytes, followed by reperfusion with a Krebs red cell solution. The deposition of leukocytes in coronary capillaries and venules was observed using intravital microscopy. Three groups were studied: nonischemic control hearts, untreated postischemic hearts reperfused at low flow, and postischemic hearts reperfused at low flow, where both the hearts and the blood reperfusate were pretreated with FCN (0.36 mg/mL blood).

Results. In the ischemia-reperfusion group, we observed a rapid and significant increase in leukocyte accumulation in both capillaries and venules. Treatment with FCN significantly reduced the leukocyte accumulation in both capillaries and venules (p < 0.05). In addition, FCN significantly reduced the persistence of leukostasis in both capillaries and venules, indicating that FCN affected a transient adhesion process.

Conclusions. These results suggest that the selectin family of leukocyte–endothelial cell adhesion proteins mediates the initial retention of leukocytes in both coronary capillaries and venules during reperfusion. Selectin blockade may be effective in reducing the contribution of leukocytes to early reperfusion injury.     

Effects of tramadol on myocardial ischemia-reperfusion injury

Objectives. The aim of the present study was to evaluate the effect of tramadol on isolated rat hearts subjected to global ischemia-reperfusion injury. Design. Langerdorff perfused isolated rat hearts were subjected to 60 min of global ischemia following 60 min of reperfusion. In group I and III hearts were received tramadol before the onset of ischemia. Following the ischemic period, group II and III hearts were received tramadol infusion. Group I and IV hearts were subjected to saline at the same time point. The myocardial postischemic recovery was compared using hemodynamic, coronary flow, biochemical parameters from coronary effluent, and oxidative stress markers from heart tissue homogenates. Results. There were significant differences between tramadol and saline used groups in hemodynamic parameters. GPx values of groups I and III were significantly lower than group IV (p<0.05). SOD values of groups I, II and III were higher than group IV (p<0.05). LDH values of groups I and II were significantly lower than groups III and IV (p<0.05). Conclusion. Tramadol provides a cardioprotective effect against myocardial ischemia-reperfusion in isolated rat heart.     

大剂量抑肽酶对心肌缺血再灌注损伤的保护作用

目的　探索大剂量抑肽酶对缺血再灌注离体鼠心的影响。方法　32只雄性SD大鼠随机均分为抑肽酶组(A),对照组(B)。制成离体鼠心工作模型,分别用含有抑肽酶（1×106KIU/L）和不含抑制肽酶的克氏液灌注30min,缺血停搏40min,复灌30min。缺血前及再灌注期间测定血液动力学指标、肌磷酸激酶含量、心脏干湿重比,对心肌超微结构作定性观察。结果　再灌注后,A组心功能、冠脉流量的恢复、超微结构的改善明显优于B组,肌磷酸激酶含量明显低于B组（P＜0.05）。结论　大剂量抑肽酶对缺血再灌注心肌有保护作用。     

Differences in prolonged ischemia length using ischemic preconditioning in the rabbit heart. Tolerable limitation time for surgically induced myocardial ischemia during normothermic cardiac operation

BACKGROUND: To determine the effect of the tolerable limitation time of prolonged ischemia after ischemic preconditioning on postischemic functional recovery and infarct size reduction in the rabbit heart. METHODS: White rabbits (n=30) were used for Langendorff perfusion. Control hearts were perfused at 37 degrees C for 180 min; 30 min global ischemia hearts (30GI) received 30 min global ischemia and 120 min reperfusion; IPC+30GI hearts received 5 min zero flow global ischemia and 5 min reperfusion prior to 30 min global ischemia; 20 min global ischemia hearts (20GI) received 20 min global ischemia and 120 min reperfusion; IPC+20GI hearts received 5 min zero flow global ischemia and 5 min reperfusion prior to 20 min global ischemia. RESULTS: Infarct size in the 30GI hearts was 33.5+/-4.0% and 1.7+/-0.5% in the control hearts. The 20GI hearts and IPC+30GI hearts decreased infarct size, as compared with the 30GI hearts (13.0+/-1.8% and 16.6+/-1.7%, respectively; p<0.001, 20GI vs 30GI; p<0.01, IPC+30GI vs 30GI; p>0.05, 20GI vs IPC+30GI) but did not enhance postischemic functional recovery. The IPC+20GI hearts (3.5+/-0.6%) significantly decreased infarct size as compared with the 20GI hearts (p<0.05, IPC+20GI vs 20GI), and there was no significant difference between the IPC+20GI and the control hearts (p>0.05), but the IPC+20GI hearts did not enhance postischemic functional recovery. CONCLUSIONS: A 20 min ischemia may be the tolerable limitation time of prolonged ischemia after ischemic preconditioning in an isolated rabbit heart model.     

Preconditioning effects of steroids and hyperoxia on cardiac ischemia-reperfusion injury and vascular reactivity.

OBJECTIVE: Corticosteroids and hyperoxia protect the heart against ischemia-reperfusion injury and may attenuate vascular reactivity. We hypothesized that (1) combining these two pretreatments induces an additive cardioprotection, (2) protection depends on activation of survival kinases and/or heat shock proteins, and (3) these interventions would change vascular reactivity into a more relaxed state. METHODS: Male rats were randomized (n=10 in each group): 1. control, 2. dexamethasone (3mg/kg) injected 24 and 12 h before harvesting the hearts, 3. 60 min of hyperoxia (90-95% O(2)) immediately before harvest, 4. combination of dexamethasone and hyperoxia as in groups 2 and 3. The hearts were Langendorff-perfused and exposed to 30 min of global ischemia and reperfused for 120 min. Cardiac function was monitored and infarct size determined. Isometric tension to vasoconstrictive and vasodilatory agents was measured in femoral artery rings. Phosphorylation of survival kinases (protein kinase B/AKT, extracellular signal-regulated kinases (ERK1/2), the stress-activated/c-Jun NH2 terminal kinases (SAPK/JNK) and p38 MAPK), adenosine monophosphate dependent kinase (AMPK) and expression of heat shock protein 72 (HSP72) in hearts was evaluated by immunoblotting. RESULTS: Infarct size was attenuated in all pretreated groups versus controls: 29% reduction in the combined group (p<0.01), 23% in hyperoxia group (p<0.05) and 31% in dexamethasone group (p<0.01). There was no significant difference between the treated groups. Combined pretreatment improved postischemic left ventricular end diastolic pressure compared to all other groups (p<0.001 vs controls, p=0.002 vs dexamethasone, p=0.005 vs hyperoxia). Combined pretreatment improved left ventricular developed pressure and coronary flow compared to controls (p<0.001 for both) and hyperoxia (p=0.0047 and p=0.0024, respectively). Combined pretreatment enhanced endothelium-independent relaxation (p=0.0032) compared to controls. Excepting ERK1/2 phosphorylation in the combined group during early reperfusion, there was no increased phosphorylation of the survival kinases AKT, p38, JNK, or AMPK and no increase of HSP72 expression. CONCLUSION: Combined pretreatment by hyperoxia and dexamethasone improved postischemic heart function, but did not reduce infarct size compared to single pretreatment groups. Except of a possible role of ERK1/2, protection depended neither on survival kinases nor heat shock protein 72.