Effect of Nicorandil on Cardiac Dysfunction During Reperfusion in Normotensive and Spontaneously Hypertensive Rats

The cardioprotective effect of nicorandil, an opener of ATP-sensitive potassium channels, was studied in the isolated perfused hearts of the spontaneously hypertensive rat (SHR) and normotensive Wistar-Kyoto (WKY) rat. The hearts were subjected to 30 min of global ischemia followed by 30 min of reperfusion. Controls received no drug. In the nicorandil group, the hearts were treated with 0.03 to 0.3 mmol/L nicorandil for 15 min before ischemia. Left ventricular developed pressure (LVDP and end diastolic pressure (LVEDP) at 30 min of reperfusion were significantly lower and larger, respectively, in SHR than in WKY rats. Nicorandil improved LVDP and decreased LVEDP at 30 min of reperfusion in both SHR and WKY rats dose-dependently. The hypertensive heart in the early stage is already susceptible to reperfusion-cardiac dysfunction. Nicorandil has a beneficial effect on the post-ischemic dysfunction in both SHR and WKY rats.     

Angiotensin II subtype 1 (AT1) receptors contribute to ischemic contracture and regulate chemomechanical energy transduction in isolated transgenic rat (alphaMHC-hAT1)594-17 hearts

BACKGROUND: The role of AT1 receptors in myocardial ischemia/reperfusion injury is unclear. We, therefore, investigated the effects of the AT1 receptor antagonist irbesartan (Irb) in isolated hearts of selective myocardial AT1 overexpressing transgenic [transgenic(alphaMHC-hAT1)594-17] and Sprague-Dawley rats (SD) subjected to ischemia/reperfusion injury. METHODS AND RESULTS: Hearts of 4-week-old male SD or transgenic rats were isolated and perfused with Krebs-Henseleit buffer with or without 10 microM Irb in Langendorff mode. After 15 min of stabilization, pressure-volume curves were obtained and the hearts subjected to 20 min ischemia followed by 30 min reperfusion. A second set of pressure-volume curves was obtained thereafter. Left ventricular developed pressure (LVDP), end-diastolic pressure (LVEDP), total coronary flow (CF) and oxygen consumption (MVO2) were recorded continuously. Myocardial efficiency was derived from the slope of relations of MVO2 to pressure/volume area. After 20 min ischemia, LVEDP was significantly higher in transgenic than in SD (35.7+/-1.8 vs. 29.2+/-1.0 mmHg, P<0.05) or Irb treated transgenic hearts (24.3+/-1.6 mmHg, P<0.05). Myocardial efficiency was increased by Irb before ischemia. Ischemia increased efficiency in SD but not in transgenic rats, Irb increased efficiency in transgenic hearts post-ischemia. CONCLUSION: Transgenic hearts developed ischemic contracture more rapidly than SD hearts as indicated by higher LVEDP during ischemia. This response was antagonized by Irb, indicating a role of AT1 receptors in ischemic contracture, AT1-receptors also appear to be involved in the control of myocardial efficiency.     

Sheng-Mai-San is protective against post-ischemic myocardial dysfunction in rats through its opening of the mitochondrial KATP channels.

The present study used isolated rat hearts to investigate whether (1) Sheng-Mei-San (SMS), a traditional Chinese formulation comprising Radix Ginseng, Radix Ophiopogonis and Fructus Schisandrae, is protective against post-ischemic myocardial dysfunction, and (2) whether the cardioprotective effect of SMS is related to scavenging of hydroxyl radicals and opening the mitochondrial KATP channels. The excised hearts of male Sprague-Dawley rats were perfused on a Langendorff apparatus with Krebs-Henseleit solution with a gas mixture of 95% O2 and 5% CO2. Left ventricular end-diastolic pressure (LVEDP, mmHg), left ventricular developed pressure (LVDP, mmHg), +/-dP/dt (mmHg/s) and coronary flow (ml/min) were continuously monitored. All hearts were perfused for a total of 120 min consisting of a 30-min pre-ischemic period followed by a 30-min global ischemia and 60-min reperfusion. Lactate, lactate dehydrogenase (LDH) and 2,5-dihydroxybenzoic acid (2,5-DHBA) concentrations in the effluent were measured during reperfusion. Three days' treatment with SMS (1.67 ml/kg per day) inhibited the rise in LVEDP and improved the post-ischemic LVDP and +/-dP/dt significantly better than in the untreated control hearts during reperfusion. SMS increased the coronary flow at baseline, and during reperfusion. Pretreatment with 5-hydroxydecanoic acid (5-HD), a mitochondrial KATP channel blocker, abolished the inhibition of the rise in LVEDP, the increase in coronary flow and the improvement in LVDP and +/-dP/dt induced by SMS. SMS significantly attenuated the concentrations of lactate, LDH and 2,5-DHBA during reperfusion, but the pretreatment with 5-HD restored them; 5-HD alone did not affect the concentrations. SMS improved the post-ischemic myocardial dysfunction through opening the mitochondrial KATP channels.     

Loss of cardioprotection induced by ischemic preconditioning after an initial ischemic period in isolated rat hearts

BACKGROUND:

The beneficial effect of ischemic preconditioning (PC) has been extensively studied in normal hearts but its effects on diseased hearts remain largely unknown. The effect of PC in the already ischemic myocardium has not been previously studied, although ischemia in varying intervals, which is difficult to assess, is often encountered in clinical practice.

OBJECTIVE:

To investigate whether the cardioprotective effect of PC is preserved when it is applied after a period of ischemia of varying duration.

METHODS:

Male Wistar rats were used for this study. Isolated normal rat hearts were perfused in Langendorff mode. Before 20 min of zero flow global ischemia followed by 45 min of reperfusion, hearts were subjected to an initial 20-min period of ischemia followed by 10 min of reperfusion (group A1); an initial 20-min period of ischemia followed by 10 min of reperfusion and two-cycle PC (3 min of ischemia, 5 min of reperfusion followed by 5 min of ischemia and 5 min of reperfusion) (group A2); and two-cycle PC followed by the initial 20-min period of ischemia and 10 min of reperfusion (group A3).Groups B and C were subjected to an initial ischemia of 15 min and 10 min, respectively, and subgroups 1, 2 and 3 were treated as above. Left ventricular end-diastolic pressure was measured at 45 min of reperfusion (LVEDP45 in mmHg). Postischemic recovery of left ventricular developed pressure was expressed as a percentage of the initial value (LVDP%).

RESULTS:

LVDP% and LVEDP45 were similar between groups A1 and A2, while when ischemic preconditioning preceded the two periods of ischemia (group A3), it resulted in significantly higher LVDP% and significantly lower LVEDP45 compared with groups A1 and A2. Left ventricular functional recovery was not increased in group B2 compared with group B1. LVDP% and LVEDP45 were similar among groups C1, C2 and C3.

CONCLUSION:

Ischemic preconditioning does not improve functional recovery in isolated rat hearts that have been initially subjected to 20 min or 15 min of zero-flow global ischemia, while an initial 10-min ischemic period seems to precondition the heart.     

“冠心颗粒”抗缺血／再灌注损伤作用及JNK蛋白信号通路在其中的调节作用

目的：观察具有抗心肌缺血／再灌注（I／R）损伤作用的中药“冠心颗粒”（GXKL）对心肌I／R损伤的拮抗作用及其可能的机制。方法：将36只SD大鼠随机分为3组：对照组,I／R组及GXKL组,每组12只大鼠。制备大鼠离体心脏心肌I／R模型再灌注30rain时,分别检测①离体心脏功能指标：左室收缩压（LVDP）、心率（HR）、左室舒张末压（LVEDP）及心室内压最大变化率（±dp／dtmax）;②心律失常评分;③应用生化法检测肌酸激酶（CK）和乳酸脱氢酶（LDH）的活性;④应用蛋白印迹法检测再灌注0min时,心肌组织中JNK的磷酸化水平。结果：与I／R组比较,GXKL组：①可明显提高I／R大鼠心肌中的±dp／dtmax[（2327．1±334．5）US．（1823．1±499．8）mmHg／s,P〈0．05],并明显改善LVDP、LVEDP等指标[LVDP：（39．6±9．1）vs．（24．2±10．1）mmHg,P〈0．05;LVEDP：（19．9±9．9）摊．（31．0±9．4）mmHg,P〈0．05];②可明显降低心律失常的评分（11．58±4．81郴．6．33±1．88,P〈0．05）;③可明显降低LDH和CK的水平[（282．2±29．6）YS．（222．9±30．2）U／L和（299．8±45．4）US．（251．9±41．8）U／L,P〈0．05];④可明显降低缺血心肌组织中磷酸化JNK的水平（0．75±0．07椰．1．54±0．10,P〈0．05）。结论：GXKL可明显改善缺血心肌抗缺血、缺氧的能力,增加心肌收缩力,减轻心律失常;其对离体心肌I／R的拮抗作用可能与JNK途径密切相关。     

Post-ischemic cardiac chamber stiffness and coronary vasomotion: the role of edema and effects of dextran

Contributions of edema to left ventricular (LV) chamber stiffness and coronary resistance after ischemia were studied in isolated buffer-perfused rabbit hearts, with constant LV chamber volume, subjected to 30 min global ischemia and 60 min reperfusion. During reperfusion hearts were perfused with standard buffer or with 3% dextran to increase oncotic pressure and decrease water content. LV chamber volume was adjusted to an initial diastolic pressure (LVEDP) of 10 mmHg. In nonischemic hearts (n = 6) LVEDP was 11 +/- 0.3 mmHg and water content was 5.0 +/- 0.1 ml/g dry weight after 90 min of perfusion. In untreated ischemic hearts (n = 8) LVEDP was 51 +/- 4 mmHg and water content was 6.0 +/- 0.1 ml/g dry weight after 60 min reperfusion (P less than 0.001 v. nonischemic). In dextran-treated ischemic hearts (n = 8) LVEDP was 38 +/- 3 mmHg (P less than 0.05 v. untreated ischemic) and water content was 5.2 +/- 0.1 ml/g dry weight (P less than 0.001 v. untreated ischemic). Coronary resistance in untreated ischemic hearts increased by 26% from 2.0 +/- 0.06 to 2.6 +/- 0.06 mmHg/ml/min after 60 min reperfusion. In treated hearts coronary resistance increased by 16% from 1.9 +/- 0.09 to 2.2 +/- 0.09 mm/Hg/ml/min (P less than 0.01 v. untreated ischemic). To determine whether the decrease in coronary resistance with dextran could be ascribed to active vasodilation, dilator responses to 2 min hypoxia or 10(-4)M adenosine were tested in nonischemic and reperfused ischemic hearts. Dilator responses were stable in nonischemic hearts or hearts reperfused after 15 min ischemia but after 30 min ischemia the dilator response to hypoxia was reduced by 72% (P less than 0.025) and the dilator response to adenosine was eliminated (P less than 0.02). Thus the response to dextran was unlike that of a direct vasodilator. These data suggest that myocardial edema plays a significant role in maintaining increased ventricular chamber stiffness and coronary resistance during reperfusion after ischemia.     

A treatment with rosuvastatin induced a reduction of arterial pressure and a decrease of oxidative stress in spontaneously hypertensive rats

The aim of this study was to appreciate consequences of rosuvastatin administration on hemodynamic function, vascular oxidative stress and ischemia/reperfusion disorders in normotensive and hypertensive rats. At 10 weeks of age, spontaneously hypertensive rats (SHR, n=20) and normotensive Wistar Kyoto male rats (WKY, n=20) were divided into four groups and given, either vehicle or 10 mg/kg/day of rosuvastatin by gavage for 3 weeks. Systolic blood pressure was assessed every week. At the end of these treatments, vascular NADPH oxidase activity was evaluated by chemiluminescence (lucigenin 0.5 microM). Hearts were isolated and perfused according to the Langendorff method and were subjected to 30 min of global ischemia. Reactive oxygen species (ROS) produced during reperfusion were quantified by electron spin resonance (ESR) spectroscopy using a spin probe (CP-H, 1 mM). After one week of treatment, rosuvastatin reduced the arterial pressure in SHR rats (180.3 +/- 2.1, SHR vs 169.7 +/- 2.3 mmHg, SHR+rosuvastatin; p < 0.01), without lowering plasma cholesterol levels; these effects were not observed in WKY. NADPH activity was 25% higher in control SHR rat aortas compared to control WKY, and was reduced by rosuvastatin in SHR rats. In isolated rat hearts subjected to ischemia/reperfusion sequences, there was a deterioration in functional parameters in control SHR compared to control WKY hearts. Rosuvastatin decreased post-ischemic contracture in WKY hearts by 50% (41.5 +/- 7.5, WKY control vs 18.4 +/- 4.6 mmHg, WKY+rosuvastatin; p < 0.01) and increased left ventricular developed pressure. This beneficial effect was accompanied by a decrease in ROS detected by ESR during reperfusion (312.5 +/- 45.3, WKY control; vs 219.3 +/- 22.9 AUC/mL, WKY+rosuvastatin; p < 0.05). In conclusion, these results are in accordance with the hypothesis that oxidative stress plays a crucial role in the pathogenesis of cardiovascular diseases including hypertension, and demonstrate the beneficial effects of rosuvastatin.     

Effects of regression of left ventricular hypertrophy following atenolol or bunazosin therapy on ischemic cardiac function and myocardial metabolism in spontaneously hypertensive rats.

The effects of regression of left ventricular hypertrophy following atenolol and bunazosin therapy on ischemic cardiac function and myocardial metabolism in spontaneously hypertensive rats (SHR) were studied. Atenolol (50 mg/kg/day) and bunazosin (5 mg/kg/day) were administered to SHR from 19 to 26 weeks of age, whereas tap water was given to control SHR and normotensive Wistar-Kyoto rats (WKY). Both atenolol and bunazosin significantly decreased arterial blood pressure and significantly decelerated the increase in left ventricular weight in SHR. At the end of the long-term treatment, hearts were removed and perfused by the working heart technique for 15 min, and then global ischemia was induced for either 10 or 30 min. The ischemic heart was reperfused for 30 min. The pressure-rate product and the extent of recovery of the coronary flow after reperfusion following 30 min of ischemia in the bunazosin-treated SHR were significantly higher than those in the control SHR and the atenolol-treated SHR. The levels of adenosine triphosphate (ATP), creatine phosphate (CrP), and energy charge potential in the SHR heart reperfused after 30 min of ischemia were significantly lower than those in the reperfused WKY. Both atenolol and bunazosin improved the restoration of ATP and CrP in SHR after reperfusion following 30 min of ischemia. In conclusion, antihypertensive therapy with either atenolol or bunazosin was effective in preventing cardiac hypertrophy and ischemic damage caused by different mechanisms. Factors resulting from stimulation of the cardiac alpha 1 adrenoceptor may play an important role in the development of hypertensive cardiac hypertrophy, just as factors resulting from stimulation of the beta 1-adrenoceptor do.     

N-Methyl-1-deoxynojirimycin (MOR-14), an α-glucosidase inhibitor, markedly improves postischemic left ventricular dysfunction

We examined whether pharmacological inhibition of glycogenolysis by N-methyl-1-deoxynojirimycin (MOR-14), a new compound which reduces the glycogenolytic rate by inhibiting the α-1,6-glucosidase activity of the glycogen-debranching enzyme, can protect the heart against postischemic left ventricular dysfunction. The hearts of male Sprague-Dawley rats were excised, and perfused on a Langendorff apparatus with Krebs-Henseleit solution with a gas mixture of 95% O₂ and 5% CO₂. The hearts were paced at 320 beats/min except during the ischemia. Left ventricular developed pressure (LVDP, mmHg), ±dP/dt (mmHg/s), and coronary flow (ml/min) were continuously monitored. All hearts were perfused for a total of 120 min including a 30-min preischemic period followed by a 30-min episode of global ischemia and 60 min reperfusion, with or without 0.5 or 2 mM of MOR-14 during the 30-min preischemic period or the first 30 min of reperfusion. In another series of experiments, the myocardial content of glycogen and lactate was measured during the 30-min episode of ischemia in groups treated with and without 2 mM of MOR-14. Preischemic but not postischemic treatment with MOR-14 significantly improved LVDP and ±dP/dt without altering coronary flow during reperfusion in a dose-dependent manner. MOR-14 significantly preserved the glycogen content and significantly attenuated the lactate accumulation during the 30-min episode of ischemia. Preischemic treatment with MOR-14 is protective against postischemic left ventricular dysfunction through the inhibition of glycogenolysis in the isolated rat heart. Received: December 14, 2000 / Accepted: June 30, 2001     

Energy Metabolism After Ischemic Preconditioning in Streptozotocin-Induced Diabetic Rat Hearts

Objectives. The aim of this study was to compare the cardioprotective effects of preconditioning in hearts from streptozotocin-induced diabetic rats with its effects in normal rat hearts.Background. The protective effect of ischemic preconditioning against myocardial ischemia may come from improved energy balance. However, it is not known whether preconditioning can also afford protection to diabetic hearts.Methods. Isolated perfused rat hearts were either subjected (preconditioned group) or not subjected (control group) to preconditioning before 30 min of sustained ischemia and 30 min of reperfusion. Preconditioning was achieved with two cycles of 5 min of ischemia followed by 5 min of reperfusion.Results. In the preconditioned groups of both normal and diabetic rats, left ventricular developed pressure, high energy phosphates, mitochondrial adenosine triphosphatase and adenine nucleotide translocase activities were significantly preserved after ischemia-reperfusion; cumulative creatine kinase release was smaller during reperfusion; and myocardial lactate content was significantly lower after sustained ischemia. However, cumulative creatine kinase release was less in the preconditioned group of diabetic rats than in the preconditioned group of normal rats. Under ischemic conditions, more glycolytic metabolites were produced in the diabetic rats (control group) than in the normal rats, and preconditioning inhibited these metabolic changes to a similar extent in both groups.Conclusions. The present study demonstrates that in both normal and diabetic rats, preservation of mitochondrial oxidative phosphorylation and inhibition of glycolysis during ischemia can contribute to preconditioning-induced cardioprotection. Furthermore, our data suggest that diabetic myocardium may benefit more from preconditioning than normal myocardium, possibly as a result of the reduced production of glycolytic metabolites during sustained ischemia and the concomitant attenuation of intracellular acidosis.     

Myocardial function in normal and spontaneously hypertensive rats during reperfusion after a period of global ischaemia

Isolated working hearts of 16 month old spontaneously hypertensive rats (SHR, n = 8) and age matched Wistar-Kyoto (WKY, n = 8) rats were exposed to 30 min global normothermic ischaemia followed by 60 min reperfusion. The hearts were routinely perfused at an afterload level of 13.3 kPa and a preload level of 1.0 kPa. The control values of left ventricular pressure, its maximal positive first derivative (dP1v/dtmax), coronary flow per gram heart tissue, and release of lactate and enzymes such as lactate dehydrogenase and aspartate aminotransferase were comparable in both groups. WKY rat hearts ejected almost twice as much perfusate per gram heart weight as the SHR hearts. In pressure-flow curves, obtained during the control period in SHR hearts, cardiac output was independent of changes in afterload, varying between 10.7 and 18.7 kPa. In contrast, in WKY rat hearts increases in afterload resulted in a progressive decrease in cardiac output. Reperfusion of the SHR hearts after 30 min of global normothermic ischaemia resulted in a poor recovery of cardiac output (13% of the control values) and dP1v/dtmax (32%) compared with the values in the WKY rat hearts (66% and 91% of the control values respectively). Reactive hyperaemia was prominent in the WKY rat hearts but completely absent in the SHR hearts. During one hour reperfusion, SHR hearts lost 3.5 times more lactate dehydrogenase and 2.5 times more aspartate aminotransferase than the WKY rat hearts. Pressure-flow curves, obtained during the reperfusion period, showed modest recovery of myocardial function of the WKY rat hearts at the lowest afterload level tested but completely depressed myocardial function of the SHR hearts at all afterload levels. Heart tissue contents of adenosine triphosphate and creatine phosphate after one hour of reperfusion were lower in the SHR than in the WKY rats, but compared with native values a comparable percentage decrease was seen in both groups of rats.     

Cardiac Mechanical Dysfunction Induced by Ischemia‐reperfusion in Perfused Heart Isolated from Stroke‐prone Spontaneously Hypertensive Rats

We investigated the difference in mechanical function after ischemia and reperfusion between Wistar‐Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) or stroke‐prone SHR (SHRSP) using the isolated working heart model, in order to examine postischemic mechanical dysfunction in the severely hypertrophied heart. Systolic blood pressure of SHRSP was higher than that of SHR and WKY, and the left ventricular wall in SHRSP was thicker than in WKY. Mechanical dysfunction of the heart during reperfusion following ischemia (11 min) in SHRSP was severer than that in SHR and WKY, and recovery of the cardiac energy charge potential (ECP) level in SHRSP was lower than that in SHR and WKY. Twenty‐five, 12 and 11 min‐ischemia in WKY, SHR and SHRSP, respectively, caused a similar level of cardiac mechanical damage. Also, the ECP levels were almost equivalent among them at the end of 20 min reperfusion following each time of ischemia. Under each ischemic condition, a Ca^{2 +}‐channel blocker, diltiazem, and an adenosine potentiator, dilazep, produced a beneficial effect on the post‐ischemic dysfunction in SHR and WKY. However, neither cardioprotective drug led to recovery of the mechanical dysfunction of the heart during reperfusion following ischemia in SHRSP. Thus, the severely hypertrophied heart such as that in SHRSP was more susceptible to cardiac reperfusion dysfunction, than the moderately hypertrophied heart such as that in SHR. These results suggest that the cardioprotective effects of drugs may be deteriorated in severe hypertrophied hearts.     

Nicorandil improves post-ischemic myocardial dysfunction in association with opening the mitochondrial K(ATP) channels and decreasing hydroxyl radicals in isolated rat hearts.

BACKGROUND: Nicorandil has been reported to induce cardioprotection by opening the mitochondrial K(ATP) channels. However, whether nicorandil affects reactive oxygen species is unclear. METHODS AND RESULTS: The hearts of male Sprague-Dawley rats were excised and perfused on a Langendorff apparatus with Krebs-Henseleit solution with a gas mixture of 95% O(2) and 5% CO(2). 1 mmol/L of nicorandil was given 10 min before ischemia. Left ventricular developed pressure (LVDP, mmHg), +/-dP/dt (mmHg/s) and coronary flow (ml/min) were continuously monitored. All hearts were perfused for a total of 120 min consisting of a 30 min pre-ischemic period, followed by a 30 min global ischemia and 60 min reperfusion with and without 5-hydroxydecanoic acid sodium salt (5-HD), a mitochondrial K(ATP) channel blocker. The concentrations of 2,3-dihydroxybenzoic acid (2,3-DHBA), an indicator of hydroxyl radicals, in the perfusate during reperfusion period were also measured. Nicorandil significantly improved LVDP and +/-dP/dt, and increased coronary flow during reperfusion. Pretreatment with 5-HD abolished the improvement of LVDP and +/-dP/dt, and the increase in coronary flow induced by nicorandil. Nicorandil significantly attenuated the concentrations of 2,3-DHBA during reperfusion, which were restored by 5-HD. CONCLUSION: Nicorandil is protective against post-ischemic left ventricular dysfunction in association with opening the mitochondrial K(ATP) channels, decreasing hydroxyl radicals and increasing coronary flow in the isolated rat heart.     

Ischemic preconditioning maintains cardioprotection in aging normotensive and spontaneously hypertensive rats

We determined whether ischemic preconditioning could reduce infarct size and improve cardiac function in both aging normotensive Wistar–Kyoto rats (WKY) and spontaneously hypertensive rats (SHR). The left anterior descending coronary artery was occluded for 1 h followed by 3 h reperfusion in aging (∼16 months old) SHR rats and age-matched WKY rats. Hearts were either preconditioned or not (control group) prior to 1 h of coronary artery occlusion. The preconditioning regimen consisted of three cycles of 3 min occlusion followed by 5 min reperfusion applied prior to the subsequent 1 h occlusion. In WKY (n = 12 each group), the risk zone was similar in the control (51 ± 2%) and preconditioned group (46 ± 2%; p = 0.1). Preconditioning significantly reduced infarct size (as a percentage of the ischemic risk zone) (24 ± 6%) compared to controls (51 ± 5%; p = 0.0026). In SHR rats (n = 9 each group), the risk zone was smaller in the preconditioning group (41 ± 3%) than in the control group (51 ± 3%; p = 0.035). Infarct size (as % of ischemic risk zone) was also significantly reduced in the preconditioned group (13 ± 4%) compared to controls (62 ± 5%; p < 0.0001). For both WKY and SHR rats, for any sized risk zone the infarct size was smaller in preconditioned hearts compared with the control hearts. Preconditioning improved aspects of LV function during ischemia and reperfusion phase in SHR rats, but these benefits were not observed in the WKY rats. Preconditioning maintains powerful cardioprotection in aging normotensive hearts as well as aging hypertrophied hearts.     

Transient pre-ischemic acidosis protects the isolated rabbit heart subjected to 30 minutes,but not 60 minutes,of global ischemia

Adenosine released during brief episodes of ischemia, due to the breakdown of ATP, is thought to be an endogenous mediator of ischemic preconditioning. In this study we sought to determine whether protons, also released from ATP during ischemia, may protect the heart from sustained ischemic insult. Experiments were performed in isolated Langendorff-perfused rabbit hearts. Proton release was simulated by a brief transient episode of preischemic acidosis. Before ischemia all hearts underwent 15 min of preischemic perfusion. Control hearts received 15 min perfusion with normal Krebs-Henseleit buffer (KHB; pH 7.39) while the short-term acidosis (STA) group received 5 min of perfusion with normal KHB followed by 5 min of perfusion with acidic buffer (pH 5.97), and then 5 min of perfusion with normal KHB. Both control and STA groups then underwent 30 min of global ischemia. A second pair of control and STA groups were subjected to 60 min of global ischemia. After global ischemia all hearts received 60 min of reperfusion. The time course of functional recovery after 30 min of ischemia was accelerated in the STA group (i.e., developed pressure in the control and STA groups at 15 min into reperfusion averaged 57±9 and 74±3 mmHg, respectively;p<0.05), and a strong trend towards lower release of creatine kinase after 30 min of global ischemia was observed in the STA group (43±7 U/g dry tissue in the STA group vs. 76±15 U/g dry tissue in the control group). However, after 60 min of global ischemia no differences in cardiac function at reperfusion were observed between control and STA groups. Our results indicate that in the isolated rabbit heart, brief acidosis affords protection against 30 min but not against 60 min of global ischemia.     

虎杖苷通过PKC对大鼠离体缺血再灌注心肌的保护作用

目的:研究虎杖苷(polydatin,PD)对大鼠离体缺血/再灌注(I/R)心肌的保护作用。方法:将40只SD大鼠随机分为4组,包括I/R组,PD(I/R+PD)组,虎杖苷+蛋白激酶C(PKC)阻断剂(I/R+PD+chelerythrine)组和PKC阻断剂(I/R+chelerythrine)组。采用Langendorff灌流法建立离体心肌I/R模型,缺血40 min,再灌注共40 min,分别测量再灌20 min以及再灌40 min时心功能和酶学指标包括:心率、左室收缩压(LVDP)、左室舒张末压(LVEDP)、心室内压最大变化速率(±dp/dtmax)及磷酸激酶(PK)、乳酸脱氢酶(LDH)浓度。结果:心肌I/R可引起心脏功能I/R+PD组±dp/dtmax的恢复率明显回升(P0.05),同时,LVEDP、LVDP等指标也有明显改善(P0.05),LDH、PK浓度在复灌20和40 min时明显低于I/R组(P0.05)。说明PD能部分抑制再灌注期PK和LDH的漏出。PD还能够显著提高I/R心肌的超氧化物歧化酶(SOD)水平,并且降低丙二醛(MDA)水平,发挥心肌保护作用。应用PKC抑制剂chelerythrine则可以消除PD的上述作用。结论:PD可能通过PKC蛋白信号转导通路对I/R心肌发挥保护作用。     

Functional and metabolic responses to ischemia in the perfused heart isolated from normotensive and spontaneously hypertensive rats

The difference between normotensive rats (WKY) and spontaneously hypertensive rats (SHR) in functional and metabolic responses to ischemia was studied. Systolic arterial blood pressure of SHR (171.2 +/- 2.9 mmHg) was significantly higher than that of WKY (135.3 +/- 1.2 mmHg), and the left ventricular mass of SHR was larger than that of WKY. Hearts isolated from either WKY or SHR were perfused by the working heart technique. Ischemia was induced by lowering the afterload pressure of the working heart. Ischemia produced cardiac arrest, and decreased the tissue levels of adenosine triphosphate and creatine phosphate in both WKY and SHR. Recovery of mechanical function of the heart during reperfusion following ischemia in SHR was better than that in WKY, while recovery of the high-energy phosphates level in SHR was less prominent than in WKY. It is postulated that hypertension has a deleterious effect on myocardial energy metabolism in ischemic heart, even when cardiac mechanical function is maintained.     

舒芬太尼对大鼠心肌缺血再灌注室性心律失常的影响

目的观察舒芬太尼预处理对大鼠心肌缺血再灌注室性心律失常的影响。方法72只大鼠随机分为假手术组(sham组)、缺血再灌注对照组(I-R组)、缺血预处理组(IPC组)和舒芬太尼不同剂量预处理组(SPC1、SPC2、SPC3组)。舒芬太尼不同预处理组分别以0.25,1,5μg/kg静脉泵注5min,停止5min,重复进行3次。于缺血前30min、缺血30min、再灌注90min时记录心电图,观察测定左室发展压(LVDP)、左室舒张末压(LVEDP),并记录缺血30min、再灌注40min内心律失常评分。并取右室心肌组织行超氧化物歧化酶(SOD)、丙二醛(MDA)测定。结果与sham组比较,I-R组LVDP、SOD降低,LVEDP、MDA升高,心律失常评分升高(P<0.05或0.01);与I-R组比较,IPC组以及SPC1、SPC2、SPC3组LVDP、SOD升高,LVEDP、MDA降低,心律失常评分降低(P<0.05或0.01)。结论舒芬太尼可模拟心脏缺血预处理作用,可降低心肌缺血再灌注室性心律失常的发生。     

Ischemic preconditioning depends on age and gender

The goal of this study was to determine if an ischemic preconditioning (IPC) protocol improved post–ischemic functional recovery of female mouse hearts. A previous study found that IPC did not occur in hearts from 10–week–old females. We studied Langendorff–perfused hearts from both 10– and 18–week–old mice (males and females). Hearts were subjected to 45 min ischemia and 45 reperfusion (I/R); IPC involved pretreatment with 3 min ischemia. We measured hemodynamics, infarct size and levels of the phosphorylated prosurvival kinase Akt (p–Akt). Similar to a previous study, for 10– week–old mice we found that the IPC protocol appreciably improved recovery of LV developed pressure (LVDP) for hearts from males but not females. However, for 18–week–old mice we found that the IPC protocol doubled the recovery of LVDP for both males and females. For both ages, hearts from females had greater recovery of LVDP and higher levels of p–Akt compared to males. Conclusions These findings are consistent with growing evidence that preconditioning induced by ischemia or other interventions can occur in hearts from females. However, for hearts from females, preconditioning depends on age. Moreover, consistent with previous studies, hearts from females have greater inherent resistance to ischemic injury, possibly involving increased signaling via p–Akt.     

腺苷对大鼠离体心脏功能及心肌细胞凋亡的影响

目的 探讨腺苷预处理对离体灌流大鼠心脏功能及心肌细胞凋亡的影响.方法 将30只雄性Wistar大鼠随机分为对照组、缺血—再灌注（IR）组、腺苷组,各10只.采用戊巴比妥钠腹腔注射麻醉,同时腹腔注射肝素,麻醉后开胸暴露心脏,快速取出心脏.用Langehdorff离体灌注大鼠心脏K-H液,腺苷组、IR组建立心肌缺血—再灌注损伤模型.对照组灌注时间为120 min;IR组灌注K-H液30min,缺血30 min,K-H液60 min;腺苷组灌注K-H液10 min,给予腺苷20 min,缺血30 min,K-H液60 min.记录实验初始和结束时左室发展压（LVDP）和平均冠脉流量（CSF）,测定心肌组织丙二醛（MDA）含量和超氧化物歧化酶（SOD）活性,TUNEL方法检测细胞凋亡.结果 IR组和腺苷组实验结束时LVDP、CSF低于实验初始（P均＜0.01）;实验结束时腺苷组、对照组的CSF均高于IR组,LVDP水平IR组＜腺苷组＜对照组,P均＜0.05.大鼠心肌组织中MDA水平IR组＞腺苷组＞对照组,P均＜0.01,腺苷组及对照组心肌组织SOD活性高于IR组,P均＜0.01.心肌细胞凋亡率IR组＞腺苷组＞对照组P＜0.01.结论 腺苷预处理能改善离体灌流大鼠心功能,其机制可能与减轻缺血-再灌注损伤和抑制心肌细胞凋亡有关.