蝙蝠葛碱对猫冠脉结扎和复灌性心律失常的影响及电生理作用

本文报道蝙蝠葛碱(Dau)对猫缺血和非缺血心脏MAP和FRP的影响及其抗心律失常作用。剂量依赖性延长猫左心室MAPD_(50)和MAPD_(90)及FRP,累积剂量9mg/kg时,分别由给药前的170±19ms,216±16ms和177±15ms延长至197±20ms,249±18ms和238±20ms。Dau5mg/kg iv,然后以0.1mg/kg·min~(-1)恒速灌注30min,可防止缺血边缘区MAPD_(50)缩短,使缺血边缘区,中心区和非缺血区FRP延长,并降低3个区域间FRP离散程度和LAD结扎和复灌引起的VF发生率和死亡率。     

Simultaneous 31P nuclear magnetic resonance spectroscopy and mechanical function in working heart models affected by drugs

A working heart model was designed which enabled simultaneous measurement of the physiological function of the heart and the levels of high-energy phosphates and inorganic phosphate, as well as intracellular pH, by high-resolution ³¹P NMR spectroscopy. Careful control of conditions, such as temperature and metallic ions, produced rabbit heart preparations that had stable work output, heart rate, and ATP levels for more than 7 hr. Rat hearts were stable for at least 3 hr. As an example of the utility of the model, the effect of ischemia and two drugs were studied. Global ischemia of a rabbit heart at 36.2°C resulted in almost complete loss of phosphocreatine (PCr) wth 7 min and slower loss of ATP, which reached a plateau at 40% of its initial concentration with 12 min. ntracellular pH fell form 7.01 to 6.03 during 21 min of ischemia. Post-ischemia, the heart's power output and ATP concentration both returned to about 70% of pre-ischemia levels, whereas PCr overshot its initial value by 33%. BRL 34915, a K⁺ channel activator, produced an age- and species-dependent negative inotropic effect in non-ischemic hearts, with only minor changes in ATP, PCr or pH. In hearts obtained from rats pretreated for 2 days with enalapril, an inhibitor of the angiotensin-converting enzyme, post-ischemia power output returned to 74 ± 7% of preischemia levels, compared with 33 ± 11% in hearts from sham-treated rats (N = 6). Enalapril also lessened the decline of ATP during 20 min of global ischemia and enhanced the recovery of ATP in post-ischemic hearts (both about 30% greater than control). ³¹P NMR of working heart preparations enable the effect of drugs and/or ischemia on intracellular energy levels to be determined concurrently with function of the heart. A reproducible method in inducing global ischemia in working hearts facilitates the study of drug effects on functional and metabolic recovery.     

The Effect of Thioridazine and Promazine in Reducing the Potassium Loss from Isolated Perfused Rat Hearts

Electrically stimulated isolated rat hearts were perfused with a Ringer solution containing a low concentration of K⁺. At the end of a control period of 20 min. the cumulative K⁺ loss from the hearts was approximately 30 meq./kg dry weight. This value was used in each experiment as reference (100 per cent) for the total loss found after a subsequent additional test period of 30 min. The addition of promazine and thioridazine to the perfusate at the end of the control period reduced the further K⁺ loss. The values found in the different groups at the end of the test period were: Control group (10 hearts): 154 ± 11.6 per cent; with promazine 10^-5 M added (8 hearts): 103 ± 5.6 per cent; with promazine 2.5 × 10^-5 M added (10 hearts): 74 ± 10.5 per cent and with thioridazine 10^-5 M added (8 hearts): 110 ± 5.8 per cent. In another type of experiments, ouabain 1.5 × 10^-6 M was added at the end of the control period. This drug caused an increased K⁺ loss (181 ± 14.2 per cent) and ventricular fibrillation in 6 out of 8 hearts. Promazine 2.5 × 10^-5 M added before ouabain, prevented the development of fibrillation in another group of 7 hearts, and also markedly reduced the K⁺ loss. It is concluded that phenothiazines reduce the K⁺ permeability of the heart muscle membranes.     

Comparison of the protective actions of Na+/H+ and Na+/Ca2+ exchange inhibitors in ischemic/reperfused rat hearts

The protective effects of the Na⁺/H⁺ exchange inhibitors amiloride, EIPA (5‐(N‐ethyl‐N‐isopropyl)‐amiloride), and HOE 694 (3‐methylsulfonyl‐4‐(1‐piperidino) benzoyl‐guanidine) and the Na⁺/Ca²⁺ exchange inhibitor, DCB (3,4‐Dichlorobenzamil) on ischemia (30 min) / reperfusion (30 min) injury were studied using Langendorff perfused rat hearts. EIPA and HOE 694 given before ischemia protected the heart during reperfusion from mechanical and metabolic disturbances. A weak protective effect was observed with amiloride, but not with DCB. The cardioprotective efficacies of these compounds correlated with their potencies as Na⁺/H⁺ exchange inhibitors as assessed by the NH₄Cl prepulse method. None of the inhibitors was effective when given at reperfusion. EIPA and HOE 694 decreased myocardial rigidity as assessed by the resting tension (RT) which elevated during reperfusion. EIPA led to a more marked attenuation of RT elevation during reperfusion rather than ischemia, whereas diltiazem, a Ca²⁺ channel blocker, suppressed RT elevation during ischemia but did not cause a further attenuation of RT during reperfusion. Treatment with EIPA as well as diltiazem before ischemia showed a direct negative chronotropic effect. Cardioprotective effects were also observed with diltiazem. These results suggest that Na⁺/H⁺ exchange plays a more important role in ischemia‐reperfusion‐induced myocardial injury than does Na⁺/Ca²⁺ exchange. The cardioprotective effects of EIPA appear to be produced by Ca²⁺ channel blockade during ischemia and by Na⁺/H⁺ exchange inhibition during reperfusion. Drug Dev. Res. 48:160–170, 1999. © 1999 Wiley‐Liss, Inc.     

Thaliporphine protects ischemic and ischemic‐reperfused rat hearts via an NO‐dependent mechanism

In ischemia or ischemia‐reperfusion (I/R), nitric oxide (NO) can potentially exert several beneficial effects. Thaliporphine, a natural alkaloid with Ca²⁺ channel‐activating and Na⁺/K⁺ channel‐blocking activities, increased NO levels and exerted cardioprotective action in ischemic or I/R rats. The role of NO in the cardioprotective actions of thaliporphine was assessed. The severity of rhythm disturbances and mortality in anesthetized rats with either coronary artery occlusion for 30 min, or 5 min followed by 30‐min reperfusion, were monitored and compared in thaliporphine‐ vs. placebo‐treated groups. Thaliporphine treatment significantly increased NO and decreased lactate dehydrogenase (LDH) levels in the blood during the end period of ischemia or I/R. These changes in NO and LDH levels by thaliporphine were associated with a reduction in the incidence and duration of ventricular tachycardia (VT) and ventricular fibrillation (VF) during ischemic or I/R period. The mortality of animals was also completely prevented by 1 × 10^–8 moles/kg of thaliporphine. In animals subjected to 4 h of left coronary artery occlusion, 1 × 10^–7 moles/kg of thaliporphine dramatic reduced cardiac infarct zone from 46 ± 6% to 7.1 ± 1.9%. Inhibition of NO synthesis with 3.7 × 10^–6 moles/kg of N^ω ‐nitro‐L‐arginine methyl ester (L‐NAME) abolished the beneficial effects of thaliporphine during 30 min or 4 h myocardial ischemia. However, the antiarrhythmic activity and mortality reduction efficacy of thaliporphine during reperfusion after 5 min of ischemia was only partially antagonized by L‐NAME. These results showed that thaliporphine efficiently exerted the cardioprotections either in acute or prolonged coronary artery occlusion or occlusion‐reperfusion situations. The fact that thaliporphine induced cardioprotective effects were abrogated by L‐NAME indicates that NO is an important mediator for the cardioprotective effects of thaliporphine in acute or prolonged ischemia, whereas antioxidant activities may contribute to the protection of I/R injury. Drug Dev. Res. 52:446–453, 2001. © 2001 Wiley‐Liss, Inc.     

Protection from AMP 579 can be added to that from either cariporide or ischemic preconditioning in ischemic rabbit heart

AMP 579, an adenosine A /A receptor agonist, is cardioprotective when administered at reperfusion. Pretreatment with the Na /H exchanger inhibitor cariporide or ischemic preconditioning (PC) also limits infarct size. To gain insight into the mechanism of AMP 579 we investigated whether its protection could be added to that from either cariporide or PC. rabbit hearts were subjected to 45 min of regional ischemia followed by 3 h of reperfusion. Infarct size in the control group was 55.8 +/- 3.9% of the risk zone. PC significantly reduced infarct size to 26.0 +/- 6.7% (p<0.05). AMP 579 (30 micro g/kg) given just before reperfusion followed by 3 micro g/kg/min infusion for 70 min also limited infarct size (32.1 +/- 1.8%,) but the combination of AMP 579 and PC showed a significantly greater limitation of infarct size (5.5 +/- 2.7%, p < 0.05). Because cariporide pretreatment was so protective (8.5 +/- 3.7% infarction), we had to increase the ischemic insult to 60 min to test for any additive effect of the combination of AMP 579 + cariporide. Infarct size in the untreated group was 66.0 +/- 4.9% of the risk zone. Cariporide (0.5 mg/kg) 5 min prior to ischemia significantly reduced infarct size to 41.5 +/- 7.7%. When cariporide pre-treatment was combined with AMP 579 at reperfusion, infarction was further limited (14.2 +/- 4.5%). Because AMP 579's protection can be added to that of either cariporide or PC, AMP 579's mechanism of protection probably differs from either of them. The combination of AMP 579 + cariporide was particularly efficacious and could be useful in the surgical setting.     

Cardioprotective actions of KC 12291 II. Delaying Na+ overload in ischemia improves cardiac function and energy status in reperfusion

The novel blocker of voltage-gated Na⁺ channels KC 12291 (1-(5-phenyl-1,2,4-thiadiazol-3-yl-oxypropyl)-3-[N-methyl-N-[2-(3,4-dimethoxyphenyl)ethyl] amino] propane hydrochloride) delays myocardial Na⁺ overload in ischemia. To test whether KC 12291 displays cardioprotective properties in the intact heart, cardiac function, energy status and intracellular pH (³¹P NMR) as well as ion homeostasis (²³Na NMR) were investigated during low-flow ischemia (100 µl/min for 36 min) followed by reperfusion. In the well-oxygenated, isolated perfused guinea pig heart, KC 12291 (1 µM) had no effect on left ventricular developed pressure (LVDP; 54±19 mmHg). KC 12291 delayed the onset and decreased the extent of ischemic contracture and markedly improved the recovery of LVDP in reperfusion [39±14 mmHg (n=4) vs 2±2 mmHg in controls (n=5)]. KC 12291 did not influence the rapid drop in phosphocreatine (PCr) following onset of ischemia but attenuated the decline in ATP. It also diminished the ischemia-induced fall in intracellular pH [6.39±0.2 (n=6) vs 6.18±0.20 in controls (n=6)]. In reperfusion, KC 12291 remarkably enhanced the recovery of PCr (84.8±9.6% vs 51.1±8.8% of baseline) and ATP (38.2±12.9% vs 23.7±9.3% of baseline). It also accelerated the recovery of intracellular pH. KC 12291 not only reduced the extent of ischemia-induced Na⁺ overload, but also enhanced Na⁺ recovery. It is concluded that KC 12291 delays contracture and reduces ATP depletion and acidosis in ischemia, and markedly improves the functional, energetic and ionic recovery in reperfusion. Blocking voltage-gated Na⁺ channels in ischemia to delay Na⁺ overload may thus constitute a promising therapeutic approach for cardioprotection.     

Mitochondrial K<Subscript>ATP</Subscript> channels participate in the limitation of infarct size by cariporide

The objective of this study is to assess the participation of mitochondrial ATP-sensitive potassium (mitoK_ATP) channels in the cardioprotective effects of the Na⁺/H⁺ exchanger (NHE-1) blocker cariporide in isolated rat hearts. Regional ischemia was induced by occlusion of left anterior descending coronary artery during 40 min followed by 2-h reperfusion (IC). Cariporide (C, 10 μΜ), or C plus 5-hydroxydecanoate (5-HD, 100 μM, a selective mitoK_ATP channel inhibitor), or C plus chelerythrine (Chele, 1 μM, a PKC inhibitor), or an opener of mitoK_ATP channels, diazoxide (Dz, 100 μM) was applied at the onset of reperfusion. Infarct size (IS) and myocardial function were evaluated. The calcium-induced permeability transition pore (mPTP) opening was determined by measuring the light scattering decrease (LSD, a.u.) in isolated mitochondria in the absence and presence of C, C + 5-HD and Dz. IS was 33 ± 2% of the risk area in IC and was significantly diminished by C (15 ± 2%, p < 0.05), which also improved myocardial function [LVDP = 58 ± 5% (IC) vs 80 ± 5% (C)] and blunted LSD [0.80 ± 0.04 (IC) vs 0.51 ± 0.04 (C) a.u.]. 5-HD and Chele were both able to abolish the cardioprotective effects of C on IS. Dz treatment decreased IS and LSD to a similar extent to that produced by C (15 ± 4% and 0.52 ± 0.04 a.u., respectively). The present data suggest that attenuation of mPTP opening after PKC-mediated mitoK_ATP channel activation is a crucial step for the cardioprotective effects of cariporide.     

ACUTE ISCHEMIC PRECONDITIONING AND HIGH SUBCHRONIC CO EXPOSURE INDEPENDENTLY INCREASE MYOCARDIAL TOLERANCE TO ISCHEMIA

This study was designed to investigate whether exposure to carbon monoxide (CO) could alter or raise the ischemic tolerance induced by preconditioning. To this end, isolated rat hearts were aerobically perfused for 20 min. Hearts were then randomized to two groups: (1) a further 20-min aerobic perfusion, and (2) ischemic preconditioning (2 cycles of 5 min of ischemia followed by 5 min of reperfusion). Hearts were then subjected to 25 min of low-flow (0.3 ml/min.) global ischemia (37°C) and 30 min of reperfusion. In parallel studies, the same protocols were performed in hearts from rats previously exposed to subchronic CO (600 ppm for 2 wk). Ischemic preconditioning accelerated the development of ischemic contracture (onset = 6.0 ± 0.3 vs. 8.6 ± 0.9 min), increased the preischemic coronary flow (19.0 ± 1.0 vs. 11.6 ± 0.6 ml/min/ g), improved contractile recovery (73.7 ± 8.9 vs. 30.8 ± 7.5%), but was without effect on reactive hyperemia (151.2 ± 4.7 vs. 149.2 ± 5.1%) and incidence of ventricular arrhythmia during reperfusion (55.6 vs. 60.0%) compared to a control group. CO exposure alone increased the baseline coronary flow (20.1 ± 1.5 vs. 12.8 ± 0.6 ml/min/g) and the contracture magnitude (54.8 ± 6.8 vs. 37.1 ± 4.8%), improved both contractile recovery (66.1 ± 6.3 vs. 30.8 ± 7.5%) and ventricular arrhythmia incidence (22.2 vs. 60.0%), and increased the hyperemic coronary flow (26.7 ± 1.5 vs. 19.1 ± 0.7%). Preconditioning after CO exposure exacerbated ischemic contracture (shorter onset and higher magnitude), and increased the reactive hyperemia (29.8 ± 1.4%), but raised the beneficial effects on contractile recovery (85.4 ± 8.4%) without alteration of ventricular tachycardia prevention (22.2%). Thus, CO-exposed hearts could be preconditioned in the same way as normal myocardium.     

降钙素基因相关肽介导缺血预适应对溶血性磷脂酰胆碱损伤心肌的保护作用

研究心脏缺血预适应(PC)对溶血性磷脂酰胆碱(LPC)损伤心肌作用的影响，并探讨降钙素基因相关肽(CGRP)在PC中的作用. 离体大鼠心脏Langendorff法灌流，记录心率，冠脉流量，左室压和左室压最大上升速率(+dp/dt_max)，并测定灌流液中肌酸磷酸激酶(CPK)含量. 结果显示，LPC能降低各项心功能指标，并使CPK释放增加；PC(缺血5 min， 再灌5min，重复3次)能减轻LPC的损伤作用；PC的心肌保护作用可被选择性CGRP受体拮抗剂CGRP_8-37所取消；预先给予CGRP或辣椒素能产生与PC相同的心肌保护作用. 对照组, LPC, PC+LPC, CGRP_8-37, CGRP_8-37+PC+LPC, CGRP+LPC, CGRP_8-37+CGRP+LPC, 辣椒素+LPC组CPK释放量分别为0.26±0.05, 2.30±0.22, 0.25±0.03, 0.30±0.08, 2.60±0.15, 0.24±0.05, 2.70±0.20和0.25±0.07 μmol·min^-1·g^-1湿组织. 这些结果提示：1) PC对LPC所致心肌损伤具有保护作用；2) PC的保护作用是由CGRP所介导；3) CGRP或辣椒素可模拟PC的保护作用.     

Glimepiride Treatment Upon Reperfusion Limits Infarct Size via the phosphatidylinositol 3-Kinase/Akt Pathway in Rabbit Hearts

The phenomenon termed postconditioning, that is, brief episodes of ischemia/reperfusion at the onset of reperfusion reduce infarct size, is thought to involve the activation of the phosphatidylinositol 3-kinase (PI3K)/Akt pathway. Treatment with a drug activating PI3K at the onset of reperfusion may confer a similar cardioprotection. The sulfonylurea glimepiride has been shown to activate PI3K in human endothelial cells. We therefore tested in rabbit hearts whether glimepiride can produce postconditioning-mimetic actions. Langendorff-perfused rabbit hearts were subjected to 30 min of global ischemia and 120 min of reperfusion, and infarct size was determined by triphenyltetrazolium staining. Phosphorylation of Akt was analyzed by Western blotting. Glimepiride (10 μM) treatment for the first 10 min of reperfusion significantly reduced infarct size from 67.2 ± 1.3% in controls to 35.8 ± 4.5% (P<0.01). This infarct size–limiting effect of glimepiride was abolished by a selective inhibitor of PI3K (5 μM LY294002, 65.4 ± 3.4%). Phosphorylation of the PI3K substrate Akt was significantly increased in glimepiride-treated hearts when compared to controls (P<0.05). Glimepiride-induced Akt phosphorylation was inhibited by LY294002. In conclusion, our study demonstrates that glimepiride treatment upon reperfusion reduces infarct size in rabbit hearts via a PI3K/Akt-mediated pathway. The postconditioning-mimetic action of glimepiride may be beneficial for the treatment of diabetic patients with ischemic heart disease.     

Na+ channel modulation and force-frequency relationship in human myocardium

The enhancement of force of contraction (FOC) following increasing frequencies of stimulation is an important mechanism of positive inotropy in human myocardium. The present study aimed to investigate the influence of alterations in Na⁺ influx on FFR in human myocardium. Isometric FOC of electrically stimulated right auricular trabeculae (AUT, n=12) from human nonfailing hearts (n=8) was measured at different stimulation rates (0.5-3 Hz) under control conditions, after increasing Na⁺ influx by the addition of (±)BDF 9148 (BDF, 3 μmol l^-1) and after decreasing Na⁺ influx by the addition of lidocaine (LIDO, 10 μmol l^-1). Additionally, the rate dependent changes in diastolic tension (DT) were measured in all experiments. Under control conditions FOC increased with increasing frequencies of stimulation. The rate at which maximal FOC was observed (SFmax) was 2.0±0.2 Hz and maximal increase in FOC (PIEmax) by increasing frequency of stimulation was +1.5±0.5 mN. After increase of Na⁺ influx by BDF (3 μmol l^-1) SFmax was decreased to 0.8±0.1 Hz (p<0.05 versus control) and PIEmax was +0.1±0.3 mN (p<0.05). When Na⁺ influx was diminished by LIDO (10 μmol l^-1) SFmax and PIEmax were increased compared to control (2.4±0.1 Hz and +4.1±0.9 mN, p<0.05 versus control). The diastolic tension (DT) of AUT at 3 Hz was not changed at higher rates in the control group and after application of LIDO (10 μmol l^-1), whereas after enhancement of Na⁺ influx by BDF there was an increase in DT of +0.7±0.2 at 3Hz (p<0.05 versus control and LIDO). An enhanced Na⁺ influx leads to a decrease in the optimal frequency and to a smaller force potentiation by higher stimulation rates which could be at least partly due to incomplete relaxation at higher frequencies, whereas a reduced Na⁺ influx is followed by opposite alterations. It is concluded that besides Ca²⁺ handling also Na⁺ influx and Na⁺ homeostasis might determine the frequency-induced force potentiation in human myocardium. Thus, the negative FFR in diseased human myocardium might result from changes in cellular Ca²⁺ or Na⁺ regulatory sites. Received: 20 November 1996 / Accepted: 21 February 1997     

KR-31762, a novel KATP channel opener, exerts cardioprotective effects by opening SarcKATP channels in rat models of ischemia/reperfusion-induced heart injury

The cardioprotective effects of KR-31762, a newly synthesized K⁺ _ATP opener, were evaluated in rat models of ischemia/reperfusion (I/R) heart injury. In isolated rat hearts subjected to 30-min global ischemia followed by 30-min reperfusion, KR-31762 (3 and 10 μM) significantly increased the left ventricular developed pressure (LVDP) and double product (heart rate × LVDP) after 30-min referfusion in a concentration-dependent manner, while decreasing the left ventricular end-diastolic pressure (LVEDP). KR-31762 also significantly increased the time to contracture (TTC) during ischemic period (20.0, 22.4 and 26.4 min for control, 3 and 10 μM, respectively), while decreasing the release of lactate dehydrogenase (LDH) from the heart during 30 min reperfusion (30.4, 14.3 and 19.7 U/g heart weight, respectively). All these parameters except LDH release were reversed by glyburide (1 μM), a nonselective blocker of K⁺ _ATP channel, but not by 5-hydroxydecanoate, a selective blocker of mitoK⁺ _ATP channel. In anesthetized rats subjected to 45-min occlusion of left anterior descending coronary artery followed by 90-min reperfusion, KR-31762 significantly decreased the infarct size (60.8, 40.5 and 37.8% for control, 0.3 and 1.0 mg/kg, iv, respectively). KR-31762 slightly relaxed the isolated rat aorta precontracted with methoxamine (IC₅₀: 23.5 μM). These results suggest that KR-31762 exerts potent cardioprotective effects through the opening of sarcolemmal K_ATP channel in rat hearts with the minimal vasorelaxant effects.     

离体大鼠心肌局部缺血/再灌注模型制备方法的改良

目的改进离体大鼠心肌局部缺血/再灌注损伤模型的制备方法。方法在传统造模的基础上进行改良,采用在结扎线下加一硬塑管打双结的方法,阻断冠状动脉左前降支,局部缺血30min,再灌注180min。分别测定改良组和传统组的心肌梗死面积、漏出液肌酸激酶(CK)活力。结果改良组梗死区/缺血危险区为(45±7)%、变异系数(CV)为15%,CK活力为(382±18)U/ml、CV为5%;传统组梗死区/缺血危险区为(43±11)%、CV为25%,CK活力为(364±30)U/ml、CV为8%。结论改进后的模型制作方法其心肌缺血稳定、可靠,技术难度低,提高了造模的成功率,较传统法具有显著的优越性。     

前列腺素介导缓激肽诱导预适应对缺血再灌心肌的保护作用(英文)

在大鼠离体心脏观察了前列腺素介导缓激肽诱导的预适应对缺血再灌心肌的保护作用．３０ｍｉｎ缺血和３０ｍｉｎ再灌引起心功能降低（左室内压和左室内压最大上升速率下降）,冠脉流量和心率降低以及肌酸激酶（ＣＰＫ）释放增加．缺血预适应（５ｍｉｎ缺血,５ｍｉｎ再灌,重复３次）能显著改善心功能,促进心率和冠脉流量的恢复,减少ＣＰＫ释放．其作用不受吲哚美辛（１０μｍｏｌ·Ｌ－１预先灌流３０ｍｉｎ）影响．预先用缓激肽（０．５μｍｏｌ·Ｌ－１）处理５ｍｉｎ产生缺血预适应样心肌保护作用,表现为促进心功能恢复,减少ＣＰＫ释放．该作用被预先灌流吲哚美辛取消．对照组,缺血再灌组,缓激肽组,吲哚美辛加缓激肽组的ＣＰＫ分别为（０．２８±０．０３）,（２．２３±０．０６）,（０．３９±０．０９）,（１．８７±０．０５）μｍｏｌ·ｍｉｎ－１·ｇ－１湿组织．结果提示：缓激肽诱导预适应对缺血再灌心肌的保护作用与促前列腺素生成有关     

Taxol prevents myocardial ischemia-reperfusion injury by inducing JNK-mediated HO-1 expression

Context: Ischemia/hypoxia and reperfusion impair mitochondria and produce a large amount of reactive oxygen species (ROS), which lead to mitochondrial and brain damage. Furthermore, heme oxygenase-1 (HO-1) as a cytoprotective gene protects cells against ROS-induced cell death in ischemia–reperfusion injury. Induction of HO-1 is involved in cytoprotective effects of taxol.

Objective: We hypothesize that taxol protects cardiac myocytes possibly by preserving myocardial mitochondrial function and inducing HO-1 expression through the JNK pathway.

Materials and methods: In this project, the perfused Langendorff hearts isolated from rats were randomly divided into five groups: control, ischemic, ischemic?+?taxol (0.1?μM), ischemic?+?taxol (0.3?μM), and ischemic?+?taxol (1?μM). Briefly, following a 15?min equilibration period, the control group was subject to normoxic perfusion for 120?min; the ischemia group, normoxic reperfusion for 120?min after 30?min ischemia; the taxol groups, normoxic reperfusion for 120?min after 30-min ischemia with taxol (0.1, 0.3, or 1?μM). The microtubule disruption score, ROS levels, and the activity of mitochondrial electron transport chain complexes I and III were examined by using immunohistochemical methods and free radical detection kits. Western blot assay was employed to study the underlying mechanisms.

Results: After Taxol treatment (0.1?µM), the ischemic microtubule disruption score was reduced to 9.8?±?1.9%. The study revealed that 0.1, 0.3, and 1?μM taxol reduced the level of ROS by 33, 46 and 51%, respectively (p?<?0.05). In additional, 0.3 and 1?μM taxol dramatically increased the activity of mitochondrial electron transport chain complex I (99.11?±?2.59, 103.49?±?3.89) and mitochondrial electron transport chain complex III (877.82?±?12.08; 907.42?±?16.21; 914.73?±?19.39, *p?<?0.05). Additionally, phosphorylation levels of JNK1 were significantly increased in the taxol group. Furthermore, the expression level of HO-1 increased with taxol treatments, which could be inhibited by the specific inhibitor of JNK, SP600125.

Discussion and conclusion: Taxol stabilized microtubules and effectively reduced ROS levels during ischemia. It also preserved the activity of mitochondrial complexes I and III. Interestingly, taxol induced the expression of HO-1 via the JNK pathway in cardiac myocytes.     

No Beneficial Effects of Isocolloidoosmotic Synthetic Colloid Addition to St. Thomas Hospital Cardioplegic Solution in Ischemia-Reperfusion Injury in Isolated Perfused Rat Hearts

• 1.Cardioplegic solutions provide the opportunity to operate on a nonbeating heart and to protect the heart against ischemic injury during cardiac surgery. The components of these solutions are constantly being modified in an effort to find the optimal solution. We studied the effects of colloidal volume replacers such as dextran, HES and gelatin as an isocolloidoosmotic addition to St. Thomas Hospital cardioplegic solution in ischemia-reperfusion injury of isolated rat hearts.
• 2.In the control group, after a stabilization period of 20 min, the hearts were arrested with St. Thomas Hospital cardioplegic solution for 3 min, then subjected to 30 min of global ischemia. Hearts then were reperfused for 10 min. In the experimental groups, the protocol was the same, but either HES 200/0.5 (50 g/L), modified fluid gelatin (30 g/l) or dextran 70 (25 g/L) were added to the St. Thomas Hospital solution.
• 3.All hearts were compared for their preischemic and postischemic contractility, heart rate, contractility rate product, coronary flow, lactate dehydrogenase, creatine phosphokinase enzyme leakage and wet/dry weight ratio.
• 4.All groups had similar contractility (for control, HES, gelatin and dextran groups the values at minute 10 of reperfusion were 59±9, 56±11%, 61±14%, 49±14% of initial values [P>0.05, respectively]) and enzyme leakage (lactate dehydrogenase 4.1±1.0, 8.1±1.5, 5.8±1.4, 3.7±1.2 [P>0.05] and for creatine phosphokinase 3.9±2.5, 6.4±3.7, 5.5±1.3, 5.5±0.8, P>0.05] IU·min⁻¹·g dry tissue⁻¹ in the reperfusion period, respectively) results as compared with the control group.
• 5.The addition of isocolloidoosmotic colloids to the cardioplegic solution did not appear to enhance the effectiveness of the crystalloid St. Thomas Hospital cardioplegic solution. If a colloid is to be chosen as a plasma replacer or an additive to priming solution in the preoperative period, or during open-heart surgery, it should be modified fluid gelatin—for no sign of cardiodepression was determined with the use of this agent.

     

Salutary actions of thromboxane synthetase inhibition during global myocardial ischemia

Summary Isolated cat hearts were perfused with blood-free Krebs-Henseleit solution for 165 min. Ischemia was induced by reducing perfusion to 0.02 ml/min/g wet heart weight for 2h followed by reperfusion at controls flows for 30 min. Hearts perfused with the thromboxane synthetase inhibitor OKY-1581 at concentrations of 5×10^–6 M were spared from the increases in circulating thromboxane B₂ occurring in untreated ischemic hearts. After reperfusion, cardiac contractile force increased to a higher level in OKY-1581 treated hearts. This was associated with a lower coronary vascular resistance than in untreated ischemic hearts. OKY-1581 treated ischemic hearts exhibited lower perfusate and higher myocardial creatine kinase (CK) activity than untreated ischemic hearts, indicative of preservation of cellular integrity. Also, OKY-1581 treated ischemic hearts showed improved lysosomal stability as evidenced by a lower tissue percent free cathepsin D activity than untreated ischemic hearts. These results are consistent with a significant role of thromboxanes in the propagation of myocardial cellular damage during ischemia.Supported in part by research grant 1 RO1 HL 25575-01 A1 from the National Heart Lung and Blood Institute of the NIH     

粉防己碱对大鼠缺血心脏左室发展压,顺应性及（+）［3H］伊拉地平结合位点的影响

目的 研究粉防己碱（Tet）对大鼠缺血再灌注心脏的左室发展压、左室顺应性和对二氢吡啶拮抗剂(+)［³H］伊拉地平结合位点的影响。以硝苯地平（Nif）作为已知药对照。方法 建立离体大鼠心脏缺血(30 min)再灌注(15 min)模型。大鼠预先ip Tet 30 mg·kg^-1, 每日2次，连续3 d，然后离体心脏给予Tet 0.18 mmol·L^-1灌流, 缺血前灌流5 min，缺血后再灌流15 min。通过连 接于压力传感器的乳胶气囊测定左室发展压（LVDP）和左室顺应性；放射配基结合法测定心脏细胞膜上的(+)［³H］伊拉地平结合位点。结果 与正常对照组相比，缺血再灌注使LVDP降低(42±6)%, 而经Tet处理的心脏只降低(8.6±0.2)%；缺血再灌注后左室顺应性显著受损, 左室舒张末压-容积曲线左移，Tet处理的心脏顺应性改变很小, 接近正常组。Scatchard作图分析, 正常组大鼠心脏细胞膜与(+)［³H］伊拉地平有高度结合位点，K_D为(0.16±0.03)nmol·L^-1，B_max为(0.93±0.30)nmol·g^-1蛋白, 缺血再灌组心脏结合位点的密度减少〔B_max为(0.48±0.14)nmol·g^-1蛋白〕, Tet组的B_max较缺血再灌组明显升高〔(0.68±0.12)nmol·g^-1蛋白〕。各组的K_D值均无明显差别。结论 Tet与Nif相似, 保护离体大鼠心脏的收缩功能和左室顺应性, 减轻缺血所致的二氢吡啶结合位点密度降低。这些效应伴随能量需求的下降因而阻止胞内钙超载, 改善缺血。     

Protection of the right ventricle from ischemia and reperfusion by preceding hypoxia

We have previously shown that 2 weeks of hypoxia protect the right ventricle of the rat heart from subsequent ischemia and reperfusion (I/R). In the present study, we examined the following: (1) Do shorter periods of hypoxia protect from subsequent I/R? (2) Does intermittent normoxia increase the cardioprotective effect? (3) Is hypoxia-inducible factor-1α (HIF-1α), erythropoietin (EPO), or vascular endothelial growth factor (VEGF) involved in the protective effects? Preischemic cardiac work was followed by global ischemia, reperfusion, and postischemic cardiac work (15 min each). External heart work was determined at the end of both work phases. Four groups of hearts were investigated: hearts from normoxic rats (n?=?8), hearts from rats after 24 h of continuous hypoxia (10.5% inspired oxygen, n?=?7), hearts from rats after 24 h hypoxia with a single intermission of 30 min normoxia (n?=?9), and hearts from rats after 24 h hypoxia and multiple intermissions of 30 min normoxia (n?=?7). Protein levels of HIF-1α and mRNA levels of EPO and VEGF were determined in right ventricular tissue of normoxic and hypoxic hearts. Postischemic right heart recovery was better in all three hypoxic groups compared with normoxic hearts (61.8?±?5.9%, 65.6?±?3.0%, and 75.7?±?2.6% vs. 46.0?±?3.9%, p?p?p?=?0.02). No differences in EPO and VEGF mRNA levels were found between normoxic and hypoxic hearts. Twenty-four hours of continuous hypoxia protect the isolated working right heart from subsequent ischemia and reperfusion. When preceding hypoxia is interrupted by multiple reoxygenation periods, there is a further significant increase in cardiac functional recovery. HIF-1α may be involved in the protective effect.