The effect of an Na+/H+ exchange inhibitor, SM-20550, on ischemia/reperfusion-induced endothelial dysfunction in isolated perfused rat hearts

The aim of this study was to test the protective effect of an Na+/H+ exchange (NHE) inhibitor, SM-20550, on ischemia/reperfusion-induced endothelial dysfunction. Isolated rat hearts were subjected to 30 min of global ischemia followed by 20 min of reperfusion and their responses to the endothelial-dependent vasodilator, acetylcholine, and the endothelial-independent vasodilator, nitroglycerin, before and after ischemia were examined. Acetylcholine-induced relaxation was impaired after ischemia/reperfusion while nitroglycerin induced relaxation was not. Administration of 1-10 nmol/l SM-20550 [N-(aminoiminomethyl)-1,4-dimethyl-1H-indole-2-carboxamide methanesulfonic acid] before and after ischemia prevented impairment of acetylcholine-induced relaxation. To further understand the mechanism of SM-20550 in protecting endothelial function, we measured the inhibitory activity of SM-20550 on NHE in cultured endothelial cells. SM-20550 (1-100 nmol/l) inhibited recovery from acidosis induced by an NH4Cl prepulse in a concentration-dependent manner. Oxygen radicals from endothelial cells and leukocytes are one of the major sources of endothelial cell injury during ischemia and reperfusion. Consequently, we tested the effect of SM-20550 on H2O2-induced endothelial cell injury. SM-20550 (100-1,000 nmol/l) prevented H2O2-induced cell injury measured by lactate dehydrogenase assay. In conclusion, SM-20550 inhibited NHE in endothelial cells, protected ischemia/reperfusion-induced endothelial dysfunction and prevented H2O2-induced endothelial cell injury at higher concentrations.     

Effect of an Na+/H+ exchange inhibitor,SM-20550, on ischemic preconditioning in rabbits

The effects of SM-20550 [N-(aminoiminomethyl)-1,4-dimethyl-1H-indole-2-carboxamide methanesulfonic acid], an Na+/H+ exchange inhibitor, on ischemic preconditioning (IPC) were studied in a rabbit model of myocardial ischemia and reperfusion injury. Anesthetized rabbits underwent occlusion of the coronary artery (30 min) followed by reperfusion (5 h). In SM-20550-treated animals, SM-20550 was intravenously administered at 0.03 mg/kg or 0.1 mg/kg before ischemia (30 min). Treatment with SM-20550 at 0.03 mg/kg had a nonsignificant tendency to reduce infarct size (18%). In contrast, 0.1 mg/kg of SM-20550 significantly reduced infarct size by 62%. In animals with IPC, the condition was induced by 2 or 5 min of ischemia and 10 min of reperfusion prior to sustained ischemia (30 min). Although 5 min of IPC significantly reduced infarct size by 72%, 2 min of IPC reduced infarct size by only 27%, which was not significant. The combination of 5 min of IPC and 0.1 mg/kg of SM-20550 significantly reduced infarct size by 78%. This reduction in infarct size was similar to that produced by 0.1 mg/kg SM-20550 or 5 min of IPC alone. Moreover, the combination of 2 min of IPC and 0.03 mg/kg of SM-20550 significantly reduced infarct size by 64%, although neither 0.03 mg/kg SM-20550 nor 2 min of IPC alone reduced infarct size significantly. These results indicate that an Na+/H+ exchange inhibitor SM-20550, does not antagonize the cardioprotective effect of IPC. SM-20550 and IPC appeared to act synergistically to exert a combined cardioprotective effect.     

Na+/H+ exchange inhibitor reduces vascular injury caused by ischemia-reperfusion in the rat hind limb

This study was designed to evaluate the effects of an Na+/H+ exchange inhibitor, SM-20550, on ischemia-reperfusion injury in the skeletal muscle. Male Sprague-Dawley rats were exposed to ischemia and reperfusion by clamping and releasing clamps both at the abdominal aorta and the bilateral femoral arteries. Rats were divided into three groups; the sham, the SM-20550 treated (SM), and the untreated control (Control) groups. In the SM and control groups, rats were exposed to 5-hr ischemia and 5-hr reperfusion. In the sham group, vessel isolation only was performed. SM-20550 (2.8 mg/kg/hr) in the SM group or vehicle in the sham and control group was continuously administered during ischemia and reperfusion periods. The wall thickness of the vessels were significantly (p<0.01) decreased in the control group than any other group. The internal diameter was significantly (p<0.01) higher in the control and SM group than in the sham group. The wall thickness/internal diameter ratio was significantly (p<0.05) lower in the control group than in the SM group. Thus, an Na+/H+ exchange inhibitor, SM-20550, ameliorated the morphological change due to ischemia reperfusion. These findings provide a clue into the mechanism of ischemia reperfusion injury.     

二氮嗪后处理对离体大鼠心功能及线粒体心磷脂的影响

目的:建立离体大鼠心肌缺血/再灌注损伤模型,观察二氮嗪(diazoxide,D)后处理对缺血/再灌注损伤离体大鼠心功能及线粒体心磷脂的影响,并探讨ATP敏感性钾通道在二氮嗪后处理心肌保护中的作用。方法:采用Langendorff装置建立离体大鼠心肌缺血/再灌注损伤模型,将SD大鼠随机分为对照组(control)、缺血再灌注模型组(I/R)、二氮嗪后处理组(I/R+D)、5-羟葵酸拮抗二氮嗪后处理组(I/R+5-HD+D),每组8只,均先灌注平衡20 min。Control组:灌注平衡后续灌70 min;I/R组:缺血前灌注4℃ST.Thomas停跳液,全心缺血40 min,再灌30 min;I/R+D组:全心缺血40 min,缺血后给予含二氮嗪(50μmol/L)的K-H液灌注5 min后,再灌25 min;I/R+5-HD+D组:二氮嗪后处理前给予含5-羟葵酸(100μmol/L)的K-H液灌注5 min,再灌20 min。观察各组续(再)灌注末心率、冠脉流出液量、心功能、心肌酶学及心肌线粒体心磷脂的变化。结果:各组续(再)灌注末比较,I/R组较control组及I/R+D组心率减慢、冠脉流出液量降低,心功能明显受损,心肌酶增加,心磷酯含量减少,但与I/R+5-HD+D无明显差异。结论:二氮嗪后处理通过增加线粒体心磷脂含量,减少心肌酶的释放,改善心脏功能,减轻心肌的再灌注损伤,产生心肌保护作用。5-羟葵酸能够完全阻断二氮嗪的心肌保护作用。     

线粒体渗透转换孔在肿瘤坏死因子α诱导的抗心肌缺氧/复氧损伤中的作用

目的：研究肿瘤坏死因子α（TNFα）诱导的抗心肌缺氧/复氧损伤的保护作用是否与抑制线粒体渗透转换孔的开放有关。 方法： 采用离体大鼠心脏灌流方法，结扎冠状动脉左前降支30 min和复氧120 min复制局部缺氧/复氧损伤模型，测定心肌梗死面积、冠脉流出液中乳酸脱氢酶（LDH）含量及各项心室力学指标。 结果： 与单纯缺氧/复氧组相比，1×104 U/L TNFα预处理明显降低心脏缺氧/复氧后的梗死面积和复氧期冠脉流出液中LDH含量，促进左室发展压、左室做功和左室舒张末压力的恢复。线粒体渗透转换孔开放剂atractyloside和钙激活钾通道阻断剂paxilline减弱了TNFα的作用。 结论： TNFα诱导的抗心肌缺氧/复氧损伤的保护作用可能与其抑制线粒体渗透转换孔的开放及促进钙激活钾通道的开放有关。     

非创伤性预处理在离体心脏抗再灌注损伤中作用机制的探讨

目的:观察非创伤性肢体缺血预处理对大鼠离体再灌注心肌是否有保护作用。方法:实验采用体重(250±30)gSD雄性大鼠25只随机分成3组,在Langendorff装置上对大鼠离体心脏进行灌流。对照组(C,n=8):在灌注全程均用富氧K-H液(充以95%O₂+5%CO₂),在恒压(8.33kPa)、恒温(37℃)条件下灌注;缺氧/复氧组(A,n=8):预灌15min后,灌注心脏先全心缺血缺氧15min,随后15min复氧再灌注(37℃);非创伤性肢体缺血预处理组(N-WIP,n=9):先将大鼠双后肢捆绑5min,松开5min,反复4次后,随后的方法同R组。在相应时点分别测定冠脉流出液和心肌匀浆中超氧化物歧化酶(SOD)活性,Ca²⁺-Mg²⁺-ATP酶活性和丙二醛(MDA)含量,同时记录心肌细胞的单相动作电位(MAP)和心肌收缩张力曲线。结果:非创伤性肢体缺血预处理能使再灌注心律失常发生率显著低于A组;心肌组织中MDA含量显著低于A组,心肌组织中SOD活性显著高于A组,心肌细胞的膜电位、Ca²⁺-Mg²⁺-ATP酶活性及肌张力较稳定。结论:非创伤性肢体缺血预处理对大鼠离体再灌注心肌有明显的保护作用,可能是通过增强心肌的抗氧化能力、稳定心肌Ca²⁺-Mg²⁺-ATP酶活性和膜相结构等途径,提高心肌细胞对再灌注损伤的抵抗力。     

Preconditioning with Na+/H+ exchange inhibitor HOE642 reduces calcium overload and exhibits marked protection on immature rabbit hearts

Inhibition of Na/H exchanger isoform-1 (NHE1) has shown significant protection in adult myocardium during ischemia/reperfusion injury; however, the effect is unclear in immature myocardium. We evaluated the effects of HOE642 (a potent, highly selective NHE1 inhibitor) preconditioning on immature rabbit hearts. Twenty immature (2-3 weeks old) New Zealand white rabbits were randomly divided into the control group (n = 10) and the HOE642 preconditioning group (n = 10). The immature isolated hearts were subjected to 45 minutes of normothermic global ischemia plus 60 minutes of reperfusion after being established on the Langendorff apparatus. During reperfusion, the recovery rates of cardiac function (LVDP, +dp/dtmax, -dp/dtmax, and coronary flow) were about 90% in the HOE642 treated group and about 50% in the control group (p < 0.05). HOE642 preconditioning can significantly decrease the release of cardiac specific enzymes CK, CK-MB and LDH (p < 0.05) and the myocardial water content (p < 0.05). Meanwhile, HOE642 markedly attenuated intracellular calcium overload (265.8 +/- 41.1 vs. 500.7 +/- 60.8 mg/kg dry wt) (p < 0.01). The blinded ultrastructural assessment under transmission electron microscopy illustrated that preconditioning with HOE642 produced evident myocyte salvage. This study demonstrates that preconditioning with HOE642 provides a significant protection during ischemia/reperfusion injury in immature myocardium, mostly by reducing myocardial calcium overload.     

Does resveratrol induce pharmacological preconditioning?

Resveratrol is a grape component with complex pharmacology related to its antioxidant activity. Little is known about the direct effects of resveratrol on the myocardium. We tested whether resveratrol administration before ischemia could attenuate ischemic/reperfusion damage. We examined how resveratrol affects high-energy phosphate metabolism (31P-nuclear magnetic resonance) and contractility of isolated Langendorff perfused rat hearts subjected to 20 min no-flow ischemia and 30 min reperfusion. During 10 min resveratrol infusion (10 microM) before ischemia, basal phosphorylation potential dropped by 40% (p < 0.05 vs. preinfusion value) without affecting contractility. The level of effluent adenosine was increased by 68%, parallel to a 50% increase in coronary flow. Resveratrol significantly improved postischemic recovery of rate-pressure product (62 +/- 5.2 vs. 23 +/- 8.1% of controls; p < 0.05). The metabolic pattern following resveratrol infusion was similar to that produced by ischemic preconditioning, suggesting that an increase in adenosine availability is involved in cardioprotection.     

Ageing exacerbates the cardiotoxicity of hydrogen peroxide through the Fenton reaction in rats

Reactive oxygen species (ROS) are involved in the post-ischemic reperfusion syndrome of the myocardium. Moreover, ageing is associated with an increased cardiac sensitivity to both ischemia and reperfusion. The aim of the present study was to determine whether the lower tolerance of aged hearts to reperfusion could be due to an increased sensitivity to the ROS that are produced during the early phase of reperfusion. For this purpose isolated perfused hearts from adult (4 months) and aged (24 months) rats were perfused with a buffer containing 150 microM of hydrogen peroxide (H(2)O(2)) in presence or absence of deferoxamine mesylate (150 microM), an iron chelator. H(2)O(2) perfusion was continued until left ventricular developed pressure had decreased up to 20% of its initial value. Ageing led to a significant reduction of the duration of the H(2)O(2) perfusion required for inducing a 80% functional alteration. Although deferoxamine did not affect this parameter in adult rats, it significantly increased the duration of H(2)O(2)-perfusion in senescent hearts (control: 14.0+/-0.9 min vs. deferoxamine: 18.1+/-1.0, P<0.05). Similarly, ageing aggravated cardiac contracture induced by H(2)O(2)-perfusion. Again, deferoxamine, which had no effect on this parameter in young adult hearts, significantly reduced the contracture of senescent rat hearts. To conclude, our data clearly show that ageing is associated with an increased sensitivity of the myocardium to hydrogen peroxide, which is partly reversed by iron chelation. These results suggest that the iron-catalyzed Fenton reaction producing hydroxyl radicals might be greater in hearts from senescent rats than in hearts from young adults.     

离体灌流大鼠心脏Na^＋／H^＋交换的意义

离体大鼠等容收缩心脏预灌流30min,再换用含20mmol/L NH_4Cl的K-H液灌流10min后,随机分为两组:(1)对照组(n=5): 恢复常规K-H液冲洗15min;(2)给药组(n=5):在常规K-H液冲洗时,加入0.5mmol/L amiloride以抑制Na~+/H~+交换。结果如下:预灌及NH_4Cl负荷阶段,两组血液动力学指标无明显差别;在冲洗时,对照组血液动力学指标逐渐恢复,而给药组心肌一直处于挛缩状态。对照组心肌组织Na~+、Ca~(2+)、K~+含量高于给药组;而心肌组织MDA及冠脉流出液中LDH活性则低于给药组。因此,酸负荷状态下,Na~+/H~+交换是pHi及生理活动恢复的重要调节机制,抑制这—过程,将加重心肌组织的损伤,以至于死亡。     

Ca2+ sensitivity of stunned myocardium after skinning using retrograde infusion of detergent

Myofilament Ca2+ desensitization contributes to the contractile dysfunction of ischemic/reperfused ("stunned") myocardium. We examined the presence of reduced Ca2+ sensitivity of isometric force in chemically skinned fibers obtained from stunned myocardium using different modes of applying the detergent Triton X-100. Langendorff-perfused rat hearts underwent 20 min ischemia/20 min reperfusion, which caused a 35 +/- 3% decrease in left ventricular developed pressure, compared to continuously perfused control hearts. Stunned and control hearts were randomly allocated to two different permeabilization protocols: In group A, trabeculae were dissected and immersed in skinning solution containing 1% Triton X-100 for 20 min. Group B hearts remained fixed to the aortic cannula and skinning solution was infused retrogradely for 6 min prior to dissection of trabeculae. Extraction of cytosolic marker proteins was more complete in group-B than in group-A preparations. Group-A preparations from stunned hearts exhibited significant Ca2+ desensitization (pCa50 = 5.07 and 5.15 in stunned and control myocardium, respectively). In group B no such difference was observed, all preparations showing higher Ca2+ sensitivity and maximum force than group-A preparations (pCa50 = 5.32 in stunned versus 5.33 in control hearts). Prolonging group-A skinning to 150 min also abolished the difference in Ca2+ sensitivity between stunned and control myocardium. In conclusion, compared to a conventional protocol, skinning by perfusion results in more complete permeabilization and better preservation of myocardial contractile function. Ischemia/reperfusion at this moderate degree of contractile dysfunction induces Ca2+ desensitization at least partially by factors that can be extracted by thorough skinning.     

Adrenocorticotrope hormone fragment (4-10) attenuates the ischemia/reperfusion-induced cardiac injury in isolated rat hearts

The aim of our study was to investigate the contribution of the adrenocorticotropic hormone fragment, ACTH (4-10), on the recovery of postischemic cardiac function. Effects of ACTH (4-10) on caspase-3 activity, cardiomyocyte and endothelial apoptosis, and HO-1 protein expression were studied. Rats were treated with various doses of ACTH (4-10), and then 12 h later, anesthetized, hearts were isolated, perfused, and subjected to 30-min ischemia followed by 120-min reperfusion. Cardiac function including heart rate, coronary flow, aortic flow, and left ventricular developed pressure were recorded. After 120-min reperfusion, 200 mug/kg of ACTH (4-10) significantly improved the recovery of aortic flow, coronary flow, and left ventricular developed pressure from their untreated control values of 15.3 +/- 0.9 ml/min, 6.5 +/- 0.9 ml/min, and 10 +/- 0.6 kPa to 20.7 +/- 1.3 ml/min, 24.8 +/- 1.8 ml/min and 13.7 +/- 0.7 kPa, respectively. Heart rate did not show significant changes during reperfusion. ACTH (4-10) treatment resulted in a reduction in infarct size, caspase 3 activity, apoptosis, and an increase in HO-1 expression. When ACTH (4-10) was given at the moment of reperfusion, the drug failed to improve the postischemic recovery of the myocardium. Thus, ACTH (4-10) can be a useful tool for the prevention of the development of ischemia/reperfusion-induced injury.     

Na+/H+ exchanger inhibition at the onset of reperfusion decreases myocardial infarct size: role of reactive oxygen species.

BACKGROUND: A burst of reactive oxygen species and activation of Na+/H+ exchanger take place at the beginning of reperfusion. The aim of this study was to assess the possible interrelation of the inhibition of Na+/H+ exchanger and reactive oxygen species about the determination of myocardial infarct size. METHODS: Isolated rat hearts were submitted to 40 min of coronary occlusion and 2 h of reperfusion. Infarct size was determined through triphenyltetrazolium chloride staining technique and was expressed as a percentage of risk area. Lipid peroxidation, as a marker of oxidative stress, was estimated by the concentration of thiobarbituric reactive substances. RESULTS: Treatment during the first 20 min of reperfusion with a selective inhibitor of Na+/H+ exchanger 1 isoform, HOE 642 (cariporide; 10 microM), significantly diminished infarct size (15.1+/-2.4% vs. 31+/-2% in untreated hearts). The administration of a "scavenger" of hydroxyl radical, N-(2-mercaptopropionyl)-glycine (2 mM), decreased infarct size in an extent similar to that of cariporide (18+/-3%). The combination cariporide+N-(2-mercaptopropionyl)-glycine did not produce additional protection (17+/-1.7%). Each intervention [HOE 642 or N-(2-mercaptopropionyl)-glycine] and its combination improved the postischemic recovery of myocardial systolic and diastolic functions in a similar extent. The content of the thiobarbituric reactive substances of untreated hearts (1012+/-144 nmol/g) decreased to 431+/-81, 390+/-82, and 433+/-41 after cariporide, N-(2-mercaptopropionyl)-glycine, and cariporide+N-(2-mercaptopropionyl)-glycine treatments, respectively. CONCLUSIONS: The present data support the conclusion that the cardioprotective effect of cariporide is associated with diminution of oxidative stress.     

Effects of volatile anesthetic preconditioning on expression of NFκB-regulated genes in aged rat myocardium

Volatile anesthetic preconditioning has been shown to be a potent way to provide myocardium protection against ischemia/reperfusion (I/R) injury; however, this cardioprotection is lost in senescent animal models and elderly patients. NFκB-regulated genes have been linked to myocardial I/R injury and anesthetic preconditioning. Here, we investigated NFκB activation related to anesthetic preconditioning in aging rat myocardium. Isolated, Langendorff perfused rat hearts from Fischer 344 male rats, 24 months old, were randomly assigned to one of the three groups. The hearts of the control group were perfused with physiologic solution without any intervention. The hearts in the I/R group were subjected to 25 minutes ischemia and followed by 60 minutes reperfusion. The hearts in the treatment group were subjected to 10 minutes 2.5% sevoflurane, followed by 20 minutes washout and by 25 minutes ischemia and 60 minutes of reperfusion, respectively. Left ventricular developed pressure (LVDP) and left ventricular enddiastolic pressure (LVEDP) were measured. Western blot analysis was used to measure inhibitor of κB (IκB) and antiapoptotic genes: A1, ILP, c-IAP-2, Bcl-2, caspase 8 and caspase 9. Ischemia and reperfusion significantly decreased LVDP and increased LVEDP in aged rat hearts. Anesthetic preconditioning with sevoflurane did not change the effects I/R on LVDP and LVEDP, despite the fact that after treatment with anesthetic preconditioning, the levels of IκB, A1, ILP, caspase 8 and caspase 9 were significantly different compared to those of the control hearts. In conclusion, anesthetic preconditioning with sevoflurane does not improve myocardial systolic and diastolic functions. Our results suggest that the activation of NFκB regulated genes is different in the senescent myocardium and could account for loss of cardioprotection with aging.     

A role for Na+/H+ exchange in pH regulation in Helix neurones

We have used the pH-sensitive fluorescent dye 8-hydroxypyrene-1,3,6-trisulphonic acid (HPTS) to reexamine the mechanisms that extrude acid from voltage-clamped Helix aspersa neurones. Intracellular acid loads were imposed by three different methods: application of weak acid, depolarization and removal of extracellular sodium. In nominally CO2/HCO3-free Ringer the rate of recovery from acid loads was significantly slowed by the potent Na+/H+ exchange inhibitor 5-[N-ethyl-N-isopropyl]-amiloride (EIPA, 50 microM). Following depolarization-induced acidifications the rate of intracellular pH (pHi) recovery was significantly reduced from 0.41 +/- 0.13 pH units.h-1 in controls to 0.12 +/- 0.09 pH units.h-1 after treatment with EIPA at pHi approximately equal to 7.3 (n = 7). The amiloride analogue also reduced the rate of acid loading seen during extracellular sodium removal both in the presence and absence of the Na(+)-dependent Cl-/HCO3- exchange inhibitor 4-acetamido-4'-isothiocyanato-stilbene-2,2'-disulphonic acid (SITS, 50 microM). This is consistent with EIPA inhibiting reverse-mode Na+/H+ exchange. In 2.5% CO2/20 mM HCO3-buffered Ringer pHi recovery was significantly inhibited by SITS, but unaffected by EIPA. Our results indicate that there are two separate Na(+)-dependent mechanisms involved in the maintenance of pHi in Helix neurones: Na(+)-dependent Cl-/HCO3- exchange and Na+/H+ exchange. Acid extrusion from Helix neurones is predominantly dependent upon the activity of Na(+)-dependent Cl-/HCO3- exchange with a lesser role for Na+/H+ exchange. This adds further weight to the belief that the Na+/H+ exchanger is ubiquitous.     

Ultrastructural alterations during the critical phase of reperfusion: a stereological study in buffer-perfused isolated rat hearts.

The present study focuses on myocardial ultrastructural alterations during the early phase of reperfusion. Isolated buffer-perfused rat hearts were exposed to standard perfusion (control group,n = 10); 60 min of global ischemia (n = 10); 60 min of global ischemia followed by 2 min of reperfusion (n = 10); or 60 min of global ischemia followed by 10 min of reperfusion (n = 10). The hearts were perfusion-fixed for electron microscopy, and ultrastructural evaluation was performed using stereological technique in order to obtain an estimate of the volume fraction and absolute volume of different tissue components. EFFECT OF ISCHEMIA: Neither the ventricular nor the myocytic volume differed significantly from the respective control values. Both the myocytic mitochondrial volume (135+/-8 vs control 89+/-6 microl) and the volume of myocytic clear space (35+/-6 vs control 10+/-2 microl) were significantly increased. The capillary volume (22+/-4 vs control 58+/-6 microl) and the volume of the capillary lumen (15+/-3 vs control 48+/-5 microl) were significantly decreased. The volume of the capillary wall, however, was not altered after exposure to ischemia (7+/-3 vs control 10+/-1 microl). ADDITIVE EFFECT OF ISCHEMIA AND REPERFUSION: Both the ventricular volume (755+/-28 vs control 600+/-32 microl) and the myocytic volume (396+/-24 vs control 287+/-16 microl) were significantly increased after 10 min of reperfusion. EFFECT OF REPERFUSION: The ischemic-induced myocytic mitochondrial swelling and increase of clear space were not reinforced during reperfusion. Furthermore, the volume of the capillary lumen and the capillary wall did not alter significantly in the groups exposed to reperfusion compared to the ischemic hearts. In conclusion, stereological evaluation did not reveal significant aggravation of ischemic-induced myocardial injury during the early phase of reperfusion.     

杭白菊提取液对抗缺血再灌注引起的离体大鼠心肌收缩功能下降

目的:观察杭白菊水提取液在缺血再灌注和缺氧/复氧过程中对离体心脏和心室肌细胞的影响,并探讨其作用机制。方法:采用Langendorff离体灌流心脏模型,观察心室收缩功能;用视频跟踪系统和细胞内双波长荧光系统分别记录单个心肌细胞收缩和i;测定心肌丙二醛(MDA)和超氧化物歧化酶(SOD)水平。结果:杭白菊(0.5g/L)可明显减轻缺血再灌注引起的离体灌流心脏左室发展压、最大收缩/舒张速率、冠脉流量和左室发展压与心率乘积的抑制作用;并明显减弱缺氧/复氧抑制心室肌细胞收缩幅度、最大收缩/舒张速度和细胞钙瞬态的作用。杭白菊处理的缺血再灌注组心肌SOD水平明显升高,MDA含量显著降低。结论:杭白菊可能通过对抗自由基的作用,从而减轻缺血再灌注和缺氧/复氧对心肌收缩功能的抑制。     

Changes in catecholamine, angiotensin converting enzyme and adenosine triphosphatase in ischemic preconditioning rat hearts

Changes in catecholamine ,angiotensin converting enzy me and adenosine triphosphatase in ischemic preconditioning rat hearts     

Delayed treatment of Na+/H+ exchange inhibitor SM-20220 reduces infarct size in both transient and permanent middle cerebral artery occlusion in rats

SM-20220 (N-(aminoiminomethyl)-1-methyl-1H-indole-2-carboxamide methanesulfonate) is a Na+/H+ exchanger (NHE) inhibitor which has been shown to attenuate cerebral edema in the rat transient focal ischemia model. However, to date, the effect of SM-20220 on cerebral infarction has not been examined. The present experiments were designed to investigate these effects, using both transient and permanent middle cerebral artery (MCA) occlusion models in rats. A dose of 1 mg/kg given intravenously 30 min after the onset of transient MCA occlusion reduced the infarcted area. In the permanent MCA occlusion model, SM-20220 reduced the infarcted area when treatment was delayed for 5, 30 or 60 min after the onset of ischemia. The present results show that NHE has a crucial role in the pathogenesis of ischemic brain damage. This NHE inhibitor may be useful for treating stroke because of its effectiveness with both forms of ischemia and because of its postischemic administration.     

Nitric oxide and peroxynitrite in postischemic myocardium

Alterations in the production of nitric oxide (NO.) are a critical factor in the injury that occurs in ischemic and reperfused myocardium; however, controversy remains regarding the alterations in NO. that occur and how these alterations cause tissue injury. As superoxide generation occurs during the early period of reperfusion, the cytotoxic oxidant peroxynitrite (ONOO-) could be formed; however, questions remain regarding ONOO- formation and its role in postischemic injury. Electron paramagnetic resonance spin trapping studies, using the NO. trap Fe(2+)-N-methyl-D-glucamine dithiocarbamate (Fe-MGD), and chemiluminescence studies, using the enhancer luminol, have been performed to measure the magnitude and time course of NO. and ONOO- formation in the normal and postischemic heart. Isolated rat hearts were subjected to control perfusion, or ischemia followed by reperfusion in the presence of Fe-MGD with electron paramagnetic resonance measurements performed on the effluent from these hearts. Whereas only trace signals were present prior to ischemia, prominent NO. adduct signals were seen during the first 2 min of reflow. The reperfusion associated increase in these NO. signals was abolished by nitric oxide synthase inhibition. In hearts perfused with luminol to detect ONOO- formation, a similar marked increase was seen during the first 2 min of reperfusion that was blocked by nitric oxide synthase inhibitors and by superoxide dismutase. Either NG-nitro-L-arginine methyl ester or superoxide dismutase treatment resulted in more than twofold higher recovery of contractile function than in untreated hearts. Immunohistology studies demonstrated that the ONOO(-)-mediated nitration product nitrotyrosine was formed in postischemic hearts, but not in normally perfused controls. Thus, NO. formation is increased during the early period of reperfusion and reacts with superoxide to form ONOO-, which results in protein nitration and myocardial injury.