Exogenous calcium preconditions myocardium from patients taking oral sulfonylurea agents.

We have previously reported that atrial trabeculae from patients taking oral sulfonylurea hypoglycemic agents cannot be preconditioned by transient ischemia, which may, in part, explain the increased cardiovascular mortality historically associated with the use of these agents (J. C. Cleveland et al., 1997, Circulation 96, 29-32). Recently, we reported that clinically accessible and acceptable exogenous Ca(2+) pretreatment protects human atrial trabeculae from subsequent ischemia (B. S. Cain et al., 1998, Ann. Thoracic Surg. 65, 1065-1070). It remains unknown whether this preconditioning strategy could confer protection to trabeculae from patients taking oral sulfonylurea drugs. We therefore hypothesized that exogenous Ca(2+) confers ischemic protection to trabeculae from patients taking oral sulfonylureas. Human atrial trabeculae were suspended in organ baths and field stimulated at 1 Hz, and force development was recorded. Following 90 min equilibration, trabeculae from patients taking oral sulfonylurea agents (n = 6 patients) were subjected to ischemia/reperfusion (I/R; 45/120 min) with or without Ca(2+) (1 mM increase x 5 min) 10 min prior to I/R. I/R decreased postischemic human myocardial contractility in trabeculae from patients on oral hypoglycemics to 15.3 +/- 2.0% baseline developed force (%BDF). Ca(2+) pretreatment increased postischemic human myocardial developed force to 35.3 +/- 2.9 %BDF in these patients (P < 0.05 vs I/R, ANOVA and Bonferroni/Dunn). We conclude that atrial muscle from patients taking oral hypoglycemic agents can be preconditioned with exogenous Ca(2+). This therapy may offer a clinically relevant means to precondition the myocardium of diabetics taking oral hypoglycemic agents prior to clinical interventions such as coronary angioplasty or cardiac bypass.     

Selective mitochondrial adenosine triphosphate-sensitive potassium channel activation is sufficient to precondition human myocardium

OBJECTIVES: Recently, the mitochondrial adenosine triphosphate-sensitive potassium channel has been suggested to be the final common effector of myocardial preconditioning. The purpose of this study is to determine whether selective mitochondrial adenosine triphosphate-sensitive potassium channel activation alone can precondition human myocardium from an ischemia/reperfusion insult. METHODS: Isolated human right atrial trabeculae were placed in tissue baths, paced, and subjected to 30 minutes of normothermic hypoxia (ischemia) followed by 45 minutes of reoxygenation (reperfusion). Trabeculae were preconditioned with a selective mitochondrial adenosine triphosphate-sensitive potassium channel opener (diazoxide 30 micromol/L) or a nonselective purinergic agonist, adenosine (125 micromol/L), for 5 minutes (adenosine) followed by a 10-minute washout period. Developed force at end reperfusion (mean +/- standard error) was compared with baseline, and tissue creatine kinase and adenosine triphosphate levels were measured after ischemia/reperfusion. RESULTS: Trabeculae subjected to ischemia/reperfusion exhibited 30% +/- 2% of baseline developed force, whereas trabeculae subjected to selective adenosine triphosphate-sensitive potassium channel opening (diazoxide) and nonselective purinergic agonist (adenosine) recovered to 55% +/- 7% and 46% +/- 3% of baseline developed force, respectively. Tissue creatine kinase activity was preserved in both the diazoxide- and adenosine-treated trabeculae (5.4 +/- 12 and 5.4 +/- 14 micromol/L per gram wet tissue) compared with ischemia/reperfusion (1.8 +/- 0.2 U/mg wet tissue). Adenosine triphosphate levels at end reperfusion were also increased in the trabeculae treated with selective (diazoxide) and nonselective (adenosine) adenosine triphosphate-sensitive potassium channel opener (4.1 +/- 0.01 and 4. 4 +/- 0.2 micromol/L per gram wet tissue) compared with trabeculae subjected to ischemia/reperfusion (1.5 +/- 0.1 micromol/L per gram wet tissue). CONCLUSIONS: These results suggest that selective mitochondrial adenosine triphosphate-sensitive potassium channel activation preconditions human myocardium and the protection conferred is equal to that of adenosine preconditioning. Targeted openers of mitochondrial adenosine triphosphate- sensitive potassium channels promote constructive protection of myocellular energy levels, contractile function, and cellular viability in human myocardium after ischemia/reperfusion.     

Selective mitochondrial KATP channel opening controls human myocardial preconditioning: too much of a good thing?

BACKGROUND: Paradoxically, patients with noninsulin-dependent diabetes mellitus experience a higher cardiovascular mortality rate than patients with insulin-dependent diabetes mellitus. We have shown that K(ATP) channel inhibition, with oral sulfonylureas, prevents myocardial preconditioning and may explain the paradox of cardiovascular death in patients with noninsulin-dependent diabetes mellitus. Cardiac preconditioning is an attractive protective strategy against any elective ischemia/reperfusion (I/R) injury. The relationship between the K(ATP) channels and human myocardial preconditioning has not previously been elucidated. METHODS: Human atrial trabeculae were harvested, placed in organ baths, and paced (1 Hz). Developed force was recorded during simulated 37 degrees C I/R (30/45 or 45/60 minutes). Before I/R, trabeculae were treated transiently with a selective mitochondrial K(ATP) channel opener for 5 minutes, followed by a 10-minute washout, or were exposed to the channel opener throughout ischemia. Recovery of function is expressed as percentage of baseline developed force. Conserved creatine kinase activity (units per gram of wet tissue) was measured at the end of reperfusion as an indicator of cellular protection. RESULTS: Transient mitochondrial K(ATP) channel opening provided protection from both I/R insults. Surprisingly, there was no protection afforded by continuous mitochondrial K(ATP) channel opening. CONCLUSIONS: Transient selective mitochondrial K(ATP) channel opening protects both viability and function of human myocardium against I/R injury, although prolonged opening of the mitochondrial K(ATP) channel does not. These results reinforce the concept of preconditioning as a transient event that must be completed before the onset of ischemia.     

肾缺血预处理对未成熟心肌的保护作用

目的探讨肾缺血预处理对未成熟心肌保护的影响，为未成熟心肌的保护提供新的方法。方法建立兔Langendorff灌注模型，将18只幼兔随机分为3组，缺血／再灌注组（I／R组）：灌注15min转为工作心15min，停灌45min，恢复灌注15min改为工作心30min；心脏缺血预处理组（CIP组）：灌注15min转为工作心15min，反复2次缺血5min再灌注5min，重复I／R组的方法；肾缺血预处理组（RIP组）：反复3次阻断左肾动脉血流5min再灌注5min，取离体心脏，灌注15min转为工作心15min，重复I／R组的方法。观察血流动力学、生化等指标。结果CIP组和RIP组的冠状动脉流量（CF）、心排血量（CO）、左心室收缩压（LVSP）恢复百分率均较I／R组升高，左心室舒张期末压（LVEDP）恢复率则较I／R组降低，差异有统计学意义（P〈0.01）；三组间比较，HR、AF恢复率差异无统计学意义（P〉0.05）；RIP组与CIP组比较各指标恢复率差异无统计学意义（P〉0．05）。RIP组与I／R组比较：心肌含水量（MWC）、血清肌酸激酶（cK）和乳酸脱氢酶（LDH）漏出率、ATP含量、丙二醛（MDA）含量、超氧化物歧化酶（SOD）活性、心肌细胞内Ca^2＋含量、心肌线粒体Ca^2＋-ATPase活性、心肌线粒体Ca^2＋含量、心肌线粒体合成ATP能力差异有统计学意义（P〈0.01），RIP组和CIP组比较各项指标差异无统计学意义（P〉0.05）。结论肾缺血预处理对未成熟心肌具有心肌保护作用。     

Mechanisms of ischemic preconditioning in skeletal muscle

BACKGROUND: Ischemic preconditioning (IP) (one or more cycles each consisting of a short period of ischemia and a short period of reperfusion, before the sustained ischemia) reduces ischemia-related organ damage in heart and skeletal muscle but the underlying mechanisms are not clear. This study was intended to assess the possible involvement of K(ATP) channels and of adenosine receptors in IP of skeletal muscle in a rat model of skeletal muscle ischemia. MATERIALS AND METHODS: Groups of 8-15 rats were given the following in vivo treatments: ischemia-reperfusion (I-R: 2.5 h tourniquet-induced ischemia of the right hindlimb, then 2 h reperfusion); IP (three cycles of 5 min ischemia, then 5 min reperfusion) before I-R; cromakalim and I-R; glibenclamide, cromakalim, and I-R; glibenclamide, IP, and I-R; [R]-N(6)-[1-methyl-2-phenylethyl]adenosine (R-PIA) and I-R; adenosine and I-R; and glibenclamide, IP, and I-R. Parameters of muscle function (postischemic maximal force, performance, contraction index, and force after 1 min of stimulation) were then assessed in vitro in the extensor digitorum longus muscle. RESULTS: Pretreatment with either IP or the K(ATP) channel opener cromakalim significantly improved postischemic muscle function. The protective effect of cromakalim was not seen when the K(ATP) channel blocker glibenclamide was added. Glibenclamide, however, did not block IP-induced protection. Pretreatment with the adenosine A(1) receptor agonist 8-(p-sulfophenyl)-theophyllin (8-SPT) or with adenosine did not improve postischemic muscle function. The adenosine receptor agonist did not block IP-induced protection against ischemic damage. CONCLUSIONS: The results show significant improvements in postischemic skeletal muscle function after IP or cromakalim pretreatment but they do not support a role for K(ATP) channels or for adenosine receptors in IP of skeletal muscle.     

Does adenosine administration during the early reperfusion period affect ischemic preconditioning?

We hypothesized that the adenosine administration during the early reperfusion period might affect ischemic preconditioning (IPC) and might reduce infarct size and enhance post-ischemic functional recovery. Twenty-four anesthetized rabbits underwent 30 min. normothermic global ischemia with 120 min. reperfusion in a buffer-perfused isolated, paced heart model and divided into four groups. Global ischemic hearts (GI, n = 6) were subjected to 30 min. global ischemia without intervention. Control hearts (n=6) were subjected to perfusion without ischemia. Ischemic preconditioned hearts (IPC, n=6) were subjected to one cycle of 5 min. global ischemia and 5 min. reperfusion prior to global ischemia. IPC + Ado hearts (n=6) received IPC and adenosine administration (100 m mol/L) during 3 min. early reperfusion period. Post-ischemic functional recovery was better in IPC + Ado hearts as compared to GI and IPC hearts, but the effect of post-ischemic functional recovery in IPC + Ado hearts became weaker during 120 min. reperfusion after prolong ischemic insult. Infarct size wre 1.0 ± 0.3% in Control hearts, 32.9 ± 5.1% in GI hearts, 13.8 ± 1.3% in IPC hearts and 8.1 ± 0.9% in IPC + Ado hearts. Infarct size in IPC hearts was significantly decreased (p<0.01) as compared to GI hearts. The reduction rate against myocardial necrosis in IPC + Ado hearts versus GI hearts was higher as compared to IPC hearts versus GI hearts (p<0.001, IPC+Ado hearts vs GI hearts; p<0.01, IPC hearts vs GI hearts; p = ns, IPC + Ado hearts vs Control hearts). These data suggest that adenosine administration during the early reperfusion period reinforce IPC effect and reduce myocardial reperfusion injury. Cardiomyoprotective effects of IPC and exogenous adenosine are exerted during early reperfusion after coronary occlusion in the isolated perfused rabbit hearts.     

Adenosine Reduces Cardiac TNF-α Production and Human Myocardial Injury Following Ischemia-Reperfusion

Myocardial tumor necrosis factor-α (TNF-α) is an autocrine contributor to myocardial dysfunction and cardiomyocyte death in ischemia-reperfusion injury (I/R), sepsis, chronic heart failure, and cardiac allograft rejection. Cardiac resident macrophages and cardiomyocytes themselves produce TNF-α. In this regard, adenosine (ADO) has been reported to reduce macrophage TNF-α production. Our purposes were to determine whether (1) I/R induces rat myocardial TNF-α production; (2) ADO decreases ischemia-induced rat myocardial TNF-α production; (3) ADO functionally protects human myocardium against I/R; and (4) TNF-α-binding protein (TNFBP; p55) confers similar protection when substituted for ADO pretreatment. To study this, human atrial trabeculae were obtained during cardiac surgery and suspended in organ baths, paced at 1 Hz, and force development was recorded during I/R (45/120 min) with or without ADO pretreatment (125 μM × 10 min), or TNFBP (1 μg/ml) during I/R. Isolated rat hearts were perfused using the Langendorff method undergoing I/R (20/40 min) with or without ADO pretreatment (125 μM × 2 min) and rat myocardial expression of TNF-α was assessed by ELISA. Results demonstrated that I/R increased rat myocardial TNF-α levels from 324 ± 36 to 902 ± 77 pg/g (P< 0.05; ANOVA and Bonferroni/Dunn) and decreased human myocardial developed force (DF) to 18 ± 2% of baseline (%BDF;P< 0.05). ADO pretreatment decreased ischemia-induced rat myocardial TNF-α production (356 ± 107 pg/g;P< 0.05) and increased postischemic DF of human myocardium to 39 ± 3% BDF (P< 0.05). Further substantiating the link between ischemia-induced TNF-α production and injury, TNFBP administration similarly improved post-I/R function of human myocardium (55 ± 5% BDF;P< 0.05 vs. I/R alone). We conclude that (1) I/R induces rat myocardial TNF-α production; (2) ADO pretreatment decreases I/R-induced rat myocardial TNF-α production; (3) ADO improves human myocardial function; (4) TNFBP confers similar protection; and (5) inhibition/ neutralization of TNF-α represents a novel strategy for protecting human myocardium against ischemia and reperfusion injury.     

Cardioprotection by anesthetics

Perioperative myocardial ischemia is one of the most important complications associated with significant risk of perioperative cardiac event. Ischemic preconditioning is a phenomenon in which single or multiple brief periods of ischemia have been shown to protect the myocardium against a more prolonged ischemic insult, the result of which is a marked reduction in myocardial infarct size, severity of myocardial stunning, or incidence of cardiac arrhythmias. Myocardial stunning is a clinically important ischemia-reperfusion injury described as a prolonged postischemic contractile dysfunction of myocardium salvaged by reperfusion. Experimental data indicate that general anesthetics protect the myocardium against ischemia-reperfusion injury, as shown by decreased infarct size and a more rapid recovery of contractile function on myocardial stunning. This phenomenon is called anesthetic preconditioning. Volatile anesthetics and morphine have a strong preconditioning like effect. The cardioprotective effect of volatile anesthetics has been supported by some clinical studies. Although the cellular mechanism of anesthetic preconditioning is not fully investigated, possible mechanism involves adenosine, adenosine receptors, the ATP-dependent potassium (K(ATP)) channels, protein kinase C, reactive oxygen species and other mediators or substances. Further, mitochondrial K(ATP) channels play the central role in anesthetic preconditioning.     

线粒体心磷脂在二氮嗪预处理减轻大鼠离体心脏缺血再灌注损伤中的作用

目的 评价线粒体心磷脂在二氮嗪预处理减轻大鼠离体心脏缺血再灌注损伤中的作用.方法 清洁级SD大鼠72只,体重200～280 g,雌雄各半,随机分为对照组(C组)、缺血再灌注组(I/R组)、二氮嗪预处理组(DZ组)和5-羟葵酸拮抗二氮嗪组(HD组),每组18只.采用Langendorff灌流装置建立大鼠离体心脏缺血再灌注模型,C组平衡灌注20 min,持续灌注100 min;I/R组平衡灌注20 min,持续灌注30 min,缺血40 min,再灌注30 min;DZ组平衡灌注20 min后,依次灌注K-H液15 min、50 μmol/L二氮嗪10 min和K-H液5 min,其余缺血再灌注同I/R组;HD组二氮嗪预处理前给予含5-羟葵酸100 μmol/L K-H液10 min,其余处理同DZ组.各组分别于平衡灌注末(T1)、缺血前即刻(T2)、再灌注末(T3)时随机取6只大鼠,监测心率(HR)、左心室发展压(LVDP)和左心室舒张末压(LVEDP),采用高效液相色谱仪测定心肌线粒体心磷脂含量.结果 与T1,2时比较,各组T3时HR、LVDP降低,LVEDP升高,心肌线粒体心磷脂含量降低(P<0.05);与C组比较,其余3组T3时HR、LVDP降低,LVEDP升高,心肌线粒体心磷脂含量降低(P<0.05);与I/R组比较,DZ组T3时HR、LVDP升高,LVEDP降低,心肌线粒体心磷脂含量升高(P<0.05);与DZ组比较,HD组T3时HR、LVDP降低,LVEDP升高,心肌线粒体心磷脂含量降低(P<0.05).结论 二氮嗪预处理可减轻大鼠离体心脏缺血再灌注损伤,与维持心肌线粒体心磷脂含量有关.     

钙预处理对未成熟心肌的保护作用

目的 观察钙预处理对未成熟心肌的影响.方法 采用Langendorff离体灌注模型,分为3组,缺血再灌组(I/R):离体心脏灌注10 win、工作心15 min后停灌45 min恢复灌注15 min,转为工作心模型30 min;心脏缺血预处理组(IPC):离体灌注10 min转为工作心15 min,反复2次缺血5min/再灌5min,停灌45min后恢复灌注15min,转为工作心模型30min;钙预处理组(CP):离体心脏灌注10 min、工作心15 min后,反复3次45 s无钙KH液灌流/5 min KH液灌流,停灌45 min后恢复灌注15 min,转为工作心模型30 min.以血流动力学指标、生化指标和心肌超微结构作为观察指标.结果 IPC与CP组比较,血流动力学指标、生化指标和心肌超微结构等方面均无明显差异;CP、IPC与I/R组比较,左心室功能恢复、三磷酸腺苷含量(ATP)(11.53±1.85、13.40±1.96比4.27±0.83,P＜0.01)、超氧化物歧化酶(SOD)活性(230.47±11.72、236.28±12.69比124.17±6.20,P＜0.01)、心肌线粒体Ca2+ATP酶活性(17.86±1.39、16.38±1.27比6.78 ±0.64,P＜0.01)和心肌线粒体合成ATP的能力(104.29±9.60、102.43±9.53比50.83±4.75,P＜0.01)明显增强,在心肌含水量(75.32±1.25、73.29±1.26比84.23±2.03,P＜0.01)、丙二醛含量(1.32±0.12、1.23±0.11比2.61±0.37,P＜0.01)、肌酸激酶(53.17±5.32、57.47±5.62比123.65±9.63,P＜0.01)和乳酸脱氢酶漏出率(32.16±3.23、34.48±3.43比85.43±5.93,P＜0.01)、心肌细胞内(2.54 ±0.32、2.17±0.22比4.48±0.74,P＜0.01)和心肌线粒体Ca2+含量(35.91±4.01、36.85±3.97比68.29±6.90,P＜0.01)明显减少;CP、IPC组心肌超微结构损伤较I/R组明显减轻.结论 钙预处理对未成熟心肌具有明显保护作用

Abstract：

Objective To investigate the protective effects of Ca2+ preconditioning on isolated immature myocardium.Methods Isolated working rabbit heart model was used,and 18 rabbits were randomly divided into 3 groups:ischemic/reperfusion (I/R) group receiving 45 min ischemia followed by 45 min reperfusion;myocardial ischemic preconditioning (IPC) group receiving 5 min ischemia and 5 min reperfusion 2 times before 45 min ischemia followed by 45 min reperfusion;Ca2 + preconditioning (CP)group receiving no-Ca2 + preconditioning before 45 min ischemia followed by 45 min reperfusion.The hemodynamics,biochemistry and myocardial ultrastructure were tested.Results The hemodynamics,biochemistry and myocardial ultrastructure had no significant diferrence between CP group and IPC group.As compared with I/R group,in CP and IPC groups,the left ventricular function recovery,adenosine triphosphate content (ATP) (11.53 ± 1.85,13.40 ± 1.96 vs 4.27 ±0.83,P＜0.01),superoxide dismutase (SOD)activity (230.47± 11.72,236.28 ± 12.69 vs 124.17 ±6.20,P＜0.01),Ca2+-ATPase activity of mitothondia ( 104.29 ± 9.60,102.43 ± 9.53 vs 50.83 ± 4.75,P＜0.01 ) and synthesized ATP activity of mitochondria ( 104.29 ±9.60,102.43 ±9.53 vs 50.83 ±4.75 ,P ＜0.01 ) were improved,and myocardial water content ( 75.32 ± 1.25,73.29 ± 1.26 vs 84.23 ± 2.03 ,P＜0.01 ),malondialdehyde content ( 1.32 ± 0.12,1.23 ± 0.11 vs 2.61 ± 0.37 ,P＜0.01 ),the dehydrogenase (32.16 ± 3.23,34.48 ± 3.43 vs 85.43 ± 5.93,P ＜0.01 ) and creatine kinase leakage (53.17 ±5.32,57.47±5.62 vs 123.65 ±9.63 ,P ＜0.01 ),myocardial cell Ca2+ content (2.54 ±0.32,2.17 ±0.22 vs 4.48 ±0.74 ,P ＜0.01 ) and mitochondrial Ca2+ content(35.91 ±4.01,36.85 ±3.97 vs 68.29 ±6.90,P ＜0.01 ) were reduced.The ultra.structure injury was milder in CP group and ICP group than in I/R group.Conclusion CP has signifcantly protective effects on immature myocardium.     

Reduction of infarct size and preservation of endothelial function by multidose intravenous adenosine during extended reperfusion

It has been proposed that infarct extension is developed from the early to the late phase of reperfusion (R). This study compares the protective effect of single or multidose administration of adenosine (Ado) on infarct size during early and late phases of R by attenuating neutrophil (PMN) recruitment. Forty-one dogs underwent 60-min left anterior descending artery (LAD) ischemia followed by 6, 24, and 48 h of R, respectively. Infarct size (%) increased over 6 to 24 h (27 +/- 2 to 38 +/- 4; P < 0.05 24 h versus 6 h group), with a corresponding increase in creatine kinase activity. Transmural myocardial blood flow (mL/min/g) decreased from 6 to 24 h (0.47 +/- 0.02 to 0.29 +/- 0.02; P < 0.05 24 h versus 6 h group). PMN localization (mm(2) myocardium) in the perinecrotic tissue detected by immunohistochemistry with anti-CD18 antibody, and accumulation detected by myeloperoxidase (MPO, DeltaAbs/min/g) increased from 6 to 24 h (292 +/- 25 to 605 +/- 44; P < 0.05 24 h versus 6 h group; and 55 +/- 7 to 96 +/- 5; P < 0.05 24 h versus 6 h group), respectively. In in vitro analysis, PMN adherence (mm(2) endothelium) to postischemic LAD increased from 98 +/- 2 to 125 +/- 3 (P < 0.05 24 h versus 6 h group) and maximal LAD endothelium-dependent relaxation (%) impaired from 6 to 24 h (74 +/- 7 to 42 +/- 10; P < 0.05 24 h versus 6 h group). Intravenous Ado (140 microg/kg/min) for 2 h at R reduced infarct size (17 +/- 2; P < 0.05 Ado versus 6 h group), CD18 positive cells (130 +/- 10; P < 0.05 Ado versus 6 h group), MPO (14 +/- 3; P < 0.05 Ado versus 6 h group), PMN adherence (57 +/- 2; P < 0.05 Ado versus 6 h group), and augmented LAD vascular relaxation (102 +/- 5 versus 74 +/- 7; P < 0.05 Ado versus 6 h group). However, this protection by Ado was lost when R was extended to 24 h. Treatment with multiple infusion of Ado at 2, 6, 12, and 18 h R significantly preserved protective effects seen at 6 h R in the Ado group. Protection by multidose Ado was still preserved when R was extended to an additional 24 h. These data suggest that interventions aiming at permanently reducing R injury may thus need to be administered not only at early R, but also during late phase. A slow wave of PMN accumulation at late R may be involved in the extension of infarction and endothelial dysfunction.     

Both ischemic and pharmacological preconditioning decrease hepatic leukocyte/endothelial cell interactions

BACKGROUND: Ischemic preconditioning has been shown to protect some tissues from ischemia/reperfusion (I/R) injury. Adenosine is believed to play an important role by attenuating leukocyte-endothelial cell adhesive interactions. Dipyridamole increases adenosine bioavailability. The purpose of this study was to evaluate the effects of mechanical (MPC) and pharmacological preconditioning (PPC) on leukocyte endothelial cell interaction in hepatic I/R injury. METHODS: C57BL6 mice were subjected to 30 min of ischemia to the left lobe of the liver. Groups tested at 30 min, 2, 5, 12, and 24 hr of reperfusion had 1) sham laparotomy (n = 10, 2) I/R (n = 25), 3) ischemic preconditioning with 5 min of ischemia and 10 min reperfusion before I/R (n = 25), and 4) (PPC) with dipyridamole (n = 25). Intravital microscopic examination was used to assess leukocyte/endothelial cell adhesion. Blood was drawn for leukocyte counts and liver function tests. RESULTS: A significant decrease in leukocyte rolling was observed at 30-min and 5-hr reperfusion intervals in the PPC and ischemic preconditioning groups compared with the I/R group. A significant decrease in leukocyte saltation was also observed in the PPC and MPC groups at 2, 5, and 12 hr of reperfusion when compared with the I/R group. aspartate aminotransferase was significantly decreased in the 5-hr preconditioning groups. There was not a significant decrease in the white blood cell count because of PPC or MPC vs. I/R CONCLUSIONS: Preconditioning decreases endothelial/ leukocyte interaction and reduces liver damage as measured by aspartate aminotransferase. These data prove that IPC and PPC provide some degree of hepatic protection in I/R injury.     

Myocardial protection with Hamburg oxygenated crystalloid cardioplegic solution for multiple coronary bypass and multivalvular replacement

We evaluated myocardial protection with Hamburg oxygenated crystalloid cardioplegic solution in a double study. Part I was a prospective metabolic study, measuring myocardial adenosine triphosphate (ATP) and creatine phosphate (CP) contents before and after ischemia in 30 coronary bypass (CABG) patients. During ischemia, CP levels decreased significantly, whereas ATP did not. After 10 minute of reperfusion, mean ATP contents were 90% of preischemic values and CP levels increased to 85% of preischemic values. Spontaneous myocardial defibrillation was seen in 93.3% of patients. Part II included evaluation of early postischemic myocardial function in 228 patients, 48 with multiple valve replacement (MUVR) and 180 with CABG. Spontaneous myocardial defibrillation was seen in 90.3%. Cardiac index, measured before and 1 and 12 hours after surgery, increased significantly in the postischemic period (from 1.95 +/- 0.9 to 2.5 +/- 0.7 l/min m2 in MUVR, p 0.04; from 2.2 +/- 0.6 to 2.7 +/- 0.7 l/min/m2 in CABG, p 0.01). Myocardial infarction frequency was 3% among CABG patients, and unrelated to the number of distal anastomosis or to aortic cross-clamp time. Early postoperative mortality was 6.2% for MUVR and 0.5% for CABG. Thus, oxygenated cardioplegia with Hamburg solution preserves high-energy phosphate compounds and prevents ischemic injury, with excellent short-term clinical results.     

Preconditioning the human heart.

The phenomenon of ischaemic preconditioning protects the myocardium by limiting infarct size in animal models of ischaemia and reperfusion. Ischaemic preconditioning may be induced by short periods of ischaemia and reperfusion. We investigated whether the human heart can be ischaemically preconditioned during coronary artery bypass grafting (CABG). Patients were enrolled into two separate studies. In the first study myocardial adenosine triphosphate (ATP) was used as the measured endpoint, assayed from myocardial biopsies taken at onset of cardiopulmonary bypass (CPB), at the end of the preconditioning stimulus, and at the end of a 10 min sustained ischaemic insult. In the second study the release of myocardial troponin T was used as the endpoint; taken at pre-CPB, and at 1, 6, 24, and 72 h after CPB. In both studies, patients were randomised into either the preconditioning group or the control group. Preconditioning was induced, after the onset of CPB, with two 3 min periods of crossclamping and an intervening 2 min of reperfusion, followed by 10 min sustained ischaemia. The control group only received 10 min of sustained ischaemia. Ischaemic preconditioning resulted in a slower rate of ATP (mumol/g dry weight) depletion in the preconditioned hearts at the end of the 10 min of sustained ischaemia (preconditioned: 11.5 +/- 0.8 vs control: 7.2 +/- 0.3; P < 0.005). Also, preconditioning resulted in a slower rate of troponin T release which was significantly different at 72 h after CPB in the preconditioned group (0.3 milligram) when compared with the control group (1.4 milligrams; P < 0.05). In addition, more patients in the preconditioned group had troponin T levels lower than 0.5 milligram at 72 h than in the control group (10 vs 3 patients). Both groups of patients received the same number of grafts, and underwent the same length of ischaemia during the procedure. We conclude that in patients undergoing CABG surgery, ischaemic preconditioning may reduce myocardial injury as shown by the favourable changes in myocardial ATP, and serum troponin T levels.     

Pharmacological preconditioning with hyperbaric oxygen: can this therapy attenuate myocardial ischemic reperfusion injury and induce myocardial protection via nitric oxide?

Ischemic reperfusion injury (IRI) is an inevitable part cardiac surgery such as coronary artery bypass graft (CABG). While ischemic hypoxia and the ensuing normoxic or hyperoxic reperfusion are critical to the initiation and propagation of IRI, conditioning myocardial cells to an oxidative stress prior to IRI may limit the consequences of this injury. Hyperbaric oxygen (HBO2) is a modality of treatment that is known to generate an oxidative stress. Studies have shown that treatment with HBO2 postischemia and reperfusion is useful in ameliorating myocardial IRI. Moreover, preconditioning the myocardium with HBO2 before reperfusion has demonstrated a myocardial protective effect by limiting the infarct size post ischemia and reperfusion. Current evidence suggests that HBO2 preconditioning may partly attenuate IRI by stimulating the endogenous production of nitric oxide (NO). As NO has the capacity to reduce neutrophil sequestration, adhesion and associated injury, and improve vascular flow, HBO2 preconditioning induced NO may play a role in providing myocardial protection during interventions that involve an inevitable episode of IRI. This current opinion review article attempts to suggest that HBO2 may be used to pharmacologically precondition and protect the myocardium from the effects of IRI that is known to occur during cardiac surgery.     

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.     

Mechanisms of sevoflurane-induced myocardial preconditioning in isolated human right atria in vitro

BACKGROUND: The authors examined the role of adenosine triphosphate-sensitive potassium channels and adenosine A(1) receptors in sevoflurane-induced preconditioning on isolated human myocardium. METHODS: The authors recorded isometric contraction of human right atrial trabeculae suspended in oxygenated Tyrode's solution (34 degrees C; stimulation frequency, 1 Hz). In all groups, a 30-min hypoxic period was followed by 60 min of reoxygenation. Seven minutes before hypoxia reoxygenation, muscles were exposed to 4 min of hypoxia and 7 min of reoxygenation or 15 min of sevoflurane at concentrations of 1, 2, and 3%. In separate groups, sevoflurane 2% was administered in the presence of 10 microm HMR 1098, a sarcolemmal adenosine triphosphate-sensitive potassium channel antagonist; 800 microm 5-hydroxy-decanoate, a mitochondrial adenosine triphosphate-sensitive potassium channel antagonist; and 100 nm 8-cyclopentyl-1,3-dipropylxanthine, an adenosine A(1) receptor antagonist. Recovery of force at the end of the 60-min reoxygenation period was compared between groups (mean +/- SD). RESULTS: Hypoxic preconditioning (90 +/- 4% of baseline) and sevoflurane 1% (82 +/- 3% of baseline), 2% (92 +/- 5% of baseline), and 3% (85 +/- 7% of baseline) enhanced the recovery of force after 60 min of reoxygenation compared with the control groups (52 +/- 9% of baseline). This effect was abolished in the presence of 5-hydroxy-decanoate (55 +/- 14% of baseline) and 8-cyclopentyl-1,3-dipropylxanthine (58 +/- 16% of baseline) but was attenuated in the presence of HMR 1098 (73 +/- 10% of baseline). CONCLUSIONS: In vitro, sevoflurane preconditions human myocardium against hypoxia through activation of adenosine triphosphate-sensitive potassium channels and stimulation of adenosine A(1) receptors.     

缺血预处理和缺血后处理对大鼠心肌缺血再灌注时炎性反应影响的比较

目的 比较缺血预处理和缺血后处理对大鼠心肌缺血再灌注时炎性反应的影响.方法 雄性SD大鼠40只,体重290～320 g,随机分为4组(n=10),缺血再灌注组(I/R组)、缺血预处理组(IPC组)和缺血后处理组(IPOC组)采用结扎左冠状动脉前降支30 min进行再灌注的方法制备心肌缺血再灌注模型,假手术组(S组)仅在左冠状动脉前降支下穿线.监测再灌注期间HR和MAP,并计算HR和MAP的乘积(心肌氧耗指数,RPP).分别于再灌注30和180 min时采集静脉血样,测定血清TNF-α、IL-6、高迁移率组蛋白1(HMGB1)和心肌肌钙蛋白I(cTnI)的浓度.采集完血样,取心肌组织,测定心肌梗死体积.结果 与S组比较,I/R组MAP和RPP降低,血清cTnI和炎性细胞因子浓度升高,心肌梗死体积增大(P＜0.05);与I/R组比较,IPC组MAP升高,IPOC组MAP和RPP均升高,两组血清cTnI和炎性细胞因子浓度降低,心肌梗死体积缩小(P＜0.05);与IPC组比较,IPOC组血清炎性细胞因子浓度升高,心肌梗死体积增大(P＜0.05).结论缺血预处理减轻大鼠心肌缺血再灌注时炎性反应的作用强于缺血后处理,从而使心肌保护效应较好.     

七氟烷预处理对大鼠心肌缺血再灌注损伤时细胞凋亡的影响

目的 探讨七氟烷预处理对大鼠心肌缺血再灌注损伤时细胞凋亡的影响.方法 成年雄性SD大鼠64只,体重270～350 g,随机分为4组(n=16):假手术组(S组)仅穿线不结扎,心肌缺血再灌注组(I/R组)阻断左冠状动脉前降支缺血30 min,恢复灌注2 h制备心肌缺血再灌注损伤模型,七氟烷组(Sevo组)吸入2.5%七氟烷30 min,七氟烷预处理+心肌缺血再灌注组(SR组)吸入2.5%七氟烷30 min,15 min后制备模型.于再灌注2 h时随机取4只大鼠处死取左心室,采用氯化三苯四唑染色法测定心肌梗死范围,随机取4只大鼠处死取左心室,采用TUNEL法检测凋亡心肌细胞,计算凋亡指数,于缺血前即刻和再灌注2 h时分别随机取4只大鼠处死取左心室,采用Western blot法测定Bcl-2及caspase-3的蛋白表达水平.结果 与S组相比,再灌注2 h时I/R组和SR组心肌梗死范围增大,心肌细胞凋亡指数升高,caspase-3蛋白表达上调,Sevo组Bcl-2蛋白表达上调,I/R组Bcl-2蛋白表达下调,Sevo组和SR组缺血前即刻Bcl-2蛋白表达上凋(P＜0.05);与I/R组相比,再灌注2 h时SR组心肌梗死范围缩小、心肌细胞凋亡指数降低,Sevo组和SR组Bcl-2蛋白表达上调,SR组caspase-3蛋白表达下调(P＜0.05);与缺血前即刻相比,I/R组和SR组再灌注2 h时Bcl-2蛋白表达下调,caspase-3蛋白表达上调(P＜0.05).结论 七氟烷预处理可通过抑制细胞凋亡减轻大鼠心肌缺血再灌注损伤.     

右美托咪啶预处理对大鼠离体心脏缺血再灌注损伤的影响

目的 评价右美托咪啶预处理对大鼠离体心脏缺血再灌注损伤的影响.方法 健康清洁级雄性Wistar大鼠24只,体重230～ 260 g,制备离体Langendorff心脏灌注模型后,采用随机数字表法,将离体心脏随机分为3组(n=8):缺血再灌注组(I/R组)、右美托咪啶Ⅰ组(DI组)、右美托咪啶Ⅱ组(DⅡ组).各组均先用K-H液平衡灌注10 min后,I/R组用K-H液继续灌注30 min,D I组和DⅡ组分别用含有0.23.、2.30ng/ml右美托咪啶的K-H液继续灌注20 min,再用K-H液冲洗10 min.各组心脏均缺血30 min,K-H液再灌注120 min.于平衡灌注末、再灌注5、30、60和120min时收集冠脉流出液,测定肌酸激酶(CK)和乳酸脱氢酶(LDH)活性.再灌注末取心肌组织,测定SOD活性及MDA含量.结果 与I/R组比较DⅠ组和DⅡ组冠脉流出液CK、LDH活性、心肌组织MDA含量降低,心肌组织SOD活性升高(P＜0.05);与DI组比较,DⅡ组冠脉流出液CK、LDH活性、心肌组织MDA含量降低,心肌组织SOD活性升高(P＜0.05).结论 右美托咪啶预处理可减轻大鼠心肌缺血再灌注损伤,且与浓度有关.