丹参对心肌缺血和再灌注损伤的保护作用

采用在家兔全麻、开胸、自主呼吸和自主心律的条件下,结扎冠脉左室支造成急性心肌缺血模型,进而松开结扎结形成再灌注损伤模型。对心肌缺血和再灌注损伤的组织脂质过氧化物含量和局部血流量变化进行测定,同时辅以心电图监护;以丹参注射液为保护剂观察其作用效果。结果表明,随着缺血时间的延续,心肌脂质过氧化物含量逐渐增加;当缺血60分钟后再灌注30分钟,脂质过氧化物含量仍继续上升,明显高于缺血60分钟组,但与缺血90分钟组比较则无显著差异;其缺血区局部组织血流量再灌注后仅恢复53.2%。给予丹参保护的再灌注组,其缺血区组织脂质过氧化物含量较再灌注损伤组下降56.0%(P<0.005),而局部组织血流量恢复则提高32.0%(P<0.001)。     

Early ischemic ultrastructural and histochemical alterations in the myocardium of the rat following coronary artery occlusion.

The early ultrastructural and histochemical changes in the myocardium following coronary artery occlusion in the rat were studied. Hearts from rats in which the left main coronary artery had been occluded for 5, 10, 20, 30, 40, 60, and 180 min were examined. Evidence of damage to myocardial cells and the microvasculature was present at 5 min of ischemia and became progressively more severe with time. Both by electron microscopic and histochemical techniques glycogen depletion was observed within 10 min of the onset of ischemia; neutral fat accumulated at 60 to 180 min of ischemia, predominately in apparently viable cells surrounding the cells with more severe ischemic injury. Loss of oxidative enzyme activity, as determined histochemically, lagged behind ultrastructural evidence of mitochondrial damage. Thus morphologic evidence of ischemic myocardial damage occurs earlier in the rat than in dogs. Wavy fibers were identified in the ischemic zone, but showed less ultrastructural damage than other cells in the same microscopic fields. By histochemical techniques, wavy fibers in the ischemic zone showed glycogen loss but still had oxidative enzyme activity 3 hr after the occlusion.     

Ultrastructural and biochemical studies of ischemic preconditioning using an adenosine receptor blocker and an ATP-sensitive K channel opener

The effect of preconditioning (PC) on acute ischemic myocardial injury was investigated in an openchest dog model. Preconditioned dogs received four 5-min occlusions of the left anterior descending coronary artery (LAD), each separated by 10 min of reperfusion. Four groups were used to assess the effect: non-PC group (G-1), PC group (G-2), 8-phenyltheophylline-(adenosine receptor blocker) infused PC group (G-3), and nicorandil- (ATP-sensitive K-channel opener) infused PC group (G-4). The LAD was occluded for 60 min, followed by 60 min of reperfusion in all dogs. The rate of ultrastructural myocardial severe injury was 26% in G-1, 0% in G-2, 5% in G-3, and 0% in G-4. Biochemical analayses also indicated higher values of myocardial contractile function in G-2 and G-4 than G-1 and G-3. These data suggest that the adenosine receptor and K channel may play a key role in PC.     

Measurement of myocardial PCO2 with a microelectrode: its relation to coronary sinus PCO2.

A micro-PCO2 electrode, with dimensions of 1 x 10 mm, and a 63% response time of 14 s was inserted into the left ventricular myocardium of the pentobarbital-anesthetized dog. Continuous recordings were made of myocardial PCO2 (PmCO2), arterial PCO2 (PaCO2), and coronary sinus PCO2 (CSPCO2) during variation of respiratory rate. PmCO2 and CSPCO2 were compared at varying coronary flow. PmCO2 was similar to and closely followed changes in CSPCO2. The difference between PmCO2 and CSPCO2 was -0.52 +/- 3.63 (SD) mmHg, and PmCO2 exceeded PaCO2 by 20.69 +/- 5.12 mmHg. After coronary occlusion, PmCO2, rose promptly, but CSPCO2 was only slightly elevated until the occlusion was released, when a CO2 efflux into the coronary sinus occurred. It is concluded that the electrode measures extracellular PCO2 and that extracellular and myocardial PCO2 are essentially equal. PmCO2 rises rapidly following coronary occlusion.     

肌酸激酶MBmass对急性心肌损伤早期诊断的实验研究

目的：连续测定犬急性心肌损伤动物模型血清中肌酸激酶MBmass（CK-MBmass）、CK-MB活性、CK活性等心肌酶学标志物,观察CK-MBmass对急性心肌损伤早期诊断的价值。方法：采用球囊堵闭左冠状动脉前降支中远端的方法建立犬急性心肌损伤动物模型。在诸闭前、堵闭后每10min直至90min连续采静脉血各2ml,3000r／min离心10min取血清测定或置-40℃保存待测。采用微粒子酶联免疫分析法测定CK-MBmass。免疫抑制法测定CK-MB活性,速率法测定CK活性。观察急性心肌损伤后CK-MBmass、CK-MB活性、CK活性等心肌酶学标志物的动态变化及损伤心肌的组织学改变。结果：冠状动脉堵闭90min后,心电图可见明显心肌损伤性ST段上抬改变;血清CK-MBmass、CK-MB活性、CK活性等指标皆超出个体值的2倍以上,但未超出实验参考值的2倍;出现异常值时间CK-MBmass、CK-MB活性、CK活性分别为（30-45）min、（30-60）min、（45-90）min。结论：CK-MBmass可早期诊断急性心肌损伤。     

Myocardial ferritin content is closely related to the degree of ischaemia

AIM: Ferritin acts as an iron scavenger and thereby may reduce iron catalysed oxygen radical production during reperfusion injury. We tested the hypothesis that the myocardial ferritin concentration is enhanced during ischaemia in proportion to the blood flow reduction. METHODS: In 10 anaesthetized, open chest Beagle dogs (six controls and four with 60 min coronary occlusion) regional myocardial blood flow (RMBF) was measured with the tracer microsphere technique and ferritin was determined in samples with an average mass of 125 mg (124-256 samples per heart). RESULTS: Under physiological conditions heart rate was 88 +/- 12 bpm, mean aortic pressure 98 +/- 8 mmHg, and RMBF 0.99 +/- 0.33 mL min-1 g-1. Data did not differ between experimental groups, P > 0.05. In the control group regional myocardial ferritin concentration averaged 11.76 +/- 3.54 ng mg-1 protein and exhibited a significant blood flow independent heterogeneity (CV(biol) = 0.27). However, between low and high flow areas (relative flow <0.5 and >1.5 times the average RMBF, respectively) no significant difference in ferritin was found, P > 0.05. In four experiments, in which regional blood flow was reduced by 40% to 0.60 +/- 0.23 mL min-1 g-1, regional ferritin content was significantly higher as compared with the control group 27.95 +/- 6.16 vs. 11.76 +/- 3.54 ng mg-1 protein, respectively. An inverse relationship was observed between ferritin and RMBF, r = -0.61, P < 0.001. Thus, a reduction of RMBF of >80% was associated with a 2.75-fold increase of the average ferritin content. Between subepicardium and subendocardium no significant difference in ferritin content was observed, neither in the control group nor in the group with induced ischaemia. Regions with control low and high flow responded similarly to the coronary constriction with regard to the local ferritin concentration: 27.88 +/- 15.22 vs. 30.10 +/- 14.91 ng mg-1, P > 0.05, respectively. A data analysis using Baye's theorem indicated that sensitivities were 0.28 and 0.94 for average flow reductions of 5 and 93%. In additional in vitro measurements (ischaemic incubation at 37 degrees C) myocardial ferritin content increased almost linearly within the first 60 min of incubation and thereafter remained unchanged. CONCLUSIONS: (1). Local physiological ferritin content in myocardium is heterogeneous and unrelated to control myocardial blood flow. (2). Ischaemia results in an enhanced ferritin content in relation to the degree of ischaemia. (3). The increase of myocardial ferritin requires a severe degree of ischaemia.     

Effects of nifedipine and niludipine on ultrastructural changes induced by coronary occlusion in dog hearts

The effects of nifedipine and niludipine on the ultrastructural changes of myocardium induced by occlusion of the left anterior descending coronary artery (LAD) were investigated in dogs anesthetized with pentobarbital. The ultrastructural changes were graded to slight, moderate, severe, and irreversible ischemic injury. Subendocardial changes were usually severe compared to subepicardial changes. Nifedipine or niludipine was injected or infused intravenously. Complete occlusion of LAD for 60 or 90 min produced severe and irreversible ischemic injury, which was not prevented by nifedipine (30 μg/kg) or niludipine (30 μg/kg) injected 5 min after occlusion. Partial occlusion of LAD (about 67% occlusion) for 90 min did not produce constant ischemic changes, and therefore the effect of drugs could not be evaluated in this ischemic model. A bolus injection (10 μg/kg, 10 min before complete LAD occlusion) followed by a constant infusion (90 μg/kg/70 min for 70 min) of nifedipine (therefore a total dose of 100 μg/kg) inhibited the degree of ischemic injury produced by the complete LAD occlusion (60 min) in the subendocardium, but not in the subepicardium. However, niludipine in the same dose (100 μg/kg) did not improve the ischemic injury induced by complete LAD occlusion in both subendo- and subepicardium.     

冠脉结扎与心肌福尔马林注射对高频成分影响的比较

以狗制作心肌缺血和心肌损伤的实验模型，观察冠脉结扎和福尔马林注射后心电高频成分的变化。共成功地完成了20条狗的实验，其中冠脉结扎12只，福尔马林注射8只。分别记录浅麻、开胸、冠脉结扎即刻、30min、60min、90min、120min以及福尔马林注射即刻、注射后30min、60min、注射60min后再结扎即刻和再结扎后30min等的心电高频成分变化。结果显示浅麻时狗心电上就存在有少量的切迹和转折，但无异常切迹。结扎后高频成分明显增多，并出现异常切迹。注射福尔马林后高频成分亦明显增多，但异常切迹却无明显增多，而注射60min后再结扎则使异常切迹明显增多。提示心电高频成分对各种心肌损伤均很敏感，而异常切迹则对损伤程度有较高的特异性。     

Regional myocardial heat-shock protein (HSP70) concentrations under different blood flow conditions

 The concentration of heat-shock proteins of 70 kD (HSP70) in heart tissue has been shown to increase during transient myocardial ischaemia and to persist during several hours of reperfusion. In this study the relationship between the local myocardial HSP70 concentration and blood flow was addressed for control physiological conditions and acute myocardial ischaemia. A specific aim of this study was to address the question of whether low flow areas under control physiological conditions have undergone a transient ischaemia during the preceding hours and thus may be in a state of hibernation or stunning. In 12 anaesthetized, open-chest beagle dogs (6 control and 6 with 60-min coronary artery stenosis) heart rate, mean aortic pressure, mean arterial partial pressure of O₂ and partial pressure of CO₂ averaged 85±16 beats/min, 94±14 mmHg, 102±17 mmHg and 39±6 mmHg, respectively. Regional HSP70 and myocardial blood flow (RMBF) were measured using an HSP70-enzyme-linked immunosorbent assay and the tracer microsphere technique, respectively, in samples of 250 mg wet mass. In the control group the mean RMBF was 1.06±0.59 ml·min^–1·g^–1 and the local HSP70 concentration was 7.08±1.03 μg/mg cytosolic protein. Myocardial HSP70 showed a blood flow-independent regional biological heterogeneity, equivalent to a coefficient of variation of 0.31. Local HSP70 concentrations did not differ (P>0.05) between control low and high flow samples, 6.16±1.0 vs 6.08±0.75 μg/mg cytosolic protein, respectively. However, after 60 min of coronary artery occlusion the local HSP70 concentration increased from 7.08 ±1.03 to 13.43±3.19 μg/mg cytosolic protein (P<0.001). There was a significant inverse relationship between the percent reduction of local blood flow and HSP70 (r=–0.56, P<0.001). From these results it is concluded that: (1) low flow samples under control physiological conditions are unlikely to be in a state of hibernation or stunning since their HSP70 concentration is normal and (2) the increase in the local HSP70 concentration during myocardial ischaemia reflects the degree of impairment of O₂ delivery. Received: 29 May 1998 / Received after revision: 14 August 1998 / Accepted: 25 August 1998     

Does nitric oxide generation contribute to the mechanism of remote ischemic preconditioning?

The protective effect of local or remote ischemic preconditioning (IPC) on subsequent 40-min ischemic and 120-min reperfusion myocardial damage was investigated. Preconditioned rats underwent one cycle of myocardial ischemia/reperfusion consisting of 5-min ischemia produced as a left coronary artery (LCA) occlusion and 5 min of reperfusion. Remote IPC was produced as 15 min of small intestinal ischemia with 15 min of reperfusion as well as 30 min of limb ischemia with 15 min of reperfusion. A marked protective action was afforded by both IPC protocols with a more significant effect of local (classic) ischemic preconditioning. Since the protective effect of remote IPC was not abolished by nitric oxide (NO) synthase inhibition with Nω-nitro- -arginine ( -NNA) it is concluded that NO generation may not be involved in the mechanism of remote IPC.     

急性心肌缺血时冠状窦血浆纤维蛋白原的改变及意义

通常人们认为,急性心肌缺血可引起血浆纤维蛋白原(Fg)的增高;但是在缺血区局部Fg的变化并不清楚。本文在17条犬上,以自制微米缩窄器造成冠脉左旋支狭窄与梗塞,观察了冠状窦Fg和血小板数(PC)的改变。结果表明:当冠脉狭窄大于75%后,急性心肌缺血可引起Fg含量的减少,当冠脉大狭窄于90%后,PC也出现减少。病理组织学检查在狭窄部位有内皮细胞的损伤、血小板的粘附及冠状动脉血栓和微血栓的形成。这一结果提示:急性心肌缺血可引起血浆Fg的减少,Fg的减少与血小板的聚集及血栓的形成有关。     

Left stellate stimulation: regional myocardial flows and ischemic injury in dogs

The effects of left stellate ganglion stimulation (LSGS) on regional myocardial blood flow (RMBF) and epicardial S-T segment were investigated in the normal and ischemic myocardium of anesthetized dogs. In nonischemic myocardium LSGS decreased calculated coronary resistance, increased RMBF, and reduced the endocardial-to-epicardial (endo-to-epi) ratio. These effects were reversed after atenolol (1 mg/kg) and abolished after combined atenolol and phenoxybenzamine (3 mg/kg) treatments. In ischemic myocardium LSGS did not change RMBF but increased S-T segment. However, after atenolol, LSGS increased ischemic RMBF and the ischemic-to-nonischemic areas flow ratio (reverse coronary steal phenomenon), these effects being abolished by phenoxybenzamine. We conclude that 1) LSGS increases RMBF and decreases endo-to-epi ratio in nonischemic areas by beta 1-adrenergic stimulation through metabolic autoregulation, 2)beta 1-adrenergic blockade in nonischemic areas unmasks alpha-adrenergic vasoconstriction inducing a redistribution of flow towards ischemic areas, and 3) further elevation of S-T segment by LSGS is due to oxygen requirements enhancement by beta 1-adrenoceptors stimulation.     

Changes in ultrasonic attenuation indicative of early myocardial ischemic injury.

This study was designed to determine whether quantitative alterations in ultrasonic attenuation are associated with myocardial changes occurring after acute ischemic injury. Five hundred seventeen regions of myocardium from 41 dogs were studied in vitro at five intervals after coronary occlusion: 15 min, 1 h, 6 h, 24 h, 3 days, and 6 wk. Quantitative indices of ultrasonic attenuation were determined from the measured frequency dependence of the ultrasonic attenuation coefficient characterizing each myocardial region over the range 2-10 MHz. Independent definition of regions of ischemic injury was provided by either creatine kinase depletion or colloidal carbon dye distribution. Results of this study indicate that ischemic myocardial regions investigated 15 min to 24 h after coronary occlusion demonstrated ultrasonic attenuation significantly decreased from nonischemic regions (P less than 0.05). In contrast, ultrasonic attenuation was significantly increased in zones of ischemia or infarction investigated at 3 days and 6 wk after coronary occlusion (P less than 0.05 and P less than 0.01, respectively). These results indicate that altered attenuation of transmitted ultrasound by myocardium in vitro is an early manifestation of ischemia.     

Ventricular arrhythmias parallel cardiac histamine efflux after coronary artery occlusion in the dog

Release of cardiac histamine by immunologic and pharmacologic stimuli is known to provoke ventricular arrhythmias. Augmented histamine efflux from ischemic myocardium has been proposed but remains controversial. The purpose of this study was to determine whether cardiac histamine efflux is precipitated by coronary artery occlusion and if so, whether histamine efflux is associated with the development of early ischemic ventricular arrhythmias. The left anterior descending coronary artery was occluded while recording a continuous electrocardiogram and coronary sinus blood was sampled frequently during the first 30 min of coronary artery occlusion in pentobarbital-anesthetized, openchest dogs. Coronary sinus histamine concentration rose from a mean baseline of 0.06±0.10 ng/ml (±SD) before coronary artery occlusion to a mean peak of 0.61±0.40 ng/ml after coronary artery occlusion (p<0.0001;n=14). The median peak coronary sinus histamine concentration was significantly greater in dogs that suffered ventricular fibrillation after coronary artery occlusion (n=4) than in those that did not (n=10) (0.86 ng/ml vs. 0.37 ng/ml;p=0.05). The area under the coronary sinus histamine concentration-vs.-time curve (total cardiac histamine efflux) correlated directly with the total number of ventricular premature contractions during the first 30 min after coronary artery occlusion (r=0.81;p<0.005;n=10), and with infarct size (r=0.91;p<0.01;n=6). Thus, during acute myocardial ischemia, the coronary sinus histamine concentration increases simultaneously with the development of early ischemic ventricular arrhythmias and in proportion to their severity.This work was supported by grants HL34215, HL37407 and HL18828 from the National Institutes of Health, Bethesda, Maryland; by a grant from the Eleanor Naylor Dana Charitable Trust, New York, New York and by General Research Funds from the Veterans Administration Medical Center, New York, New York.     

Myocardial infarction in dogs with acute and gradual occlusion of the circumflex or right coronary arteries

This study was designed to quantitate and describe the incidence and magnitude of myocardial infarction in the canine heart following acute and gradual occlusion of the circumflex or right coronary arteries. In animals with acute occlusion, the circumflex artery was ligated just distal to the bifurcation of the left coronary artery for 4 hr (seven dogs). Gradual occlusion was produced by placing an Ameroid occluder on the circumflex artery for 1 month (nine dogs), 3 months (nine dogs), and 5 months (eight dogs) and on the right coronary artery for 3 months (nine dogs). Ten dogs served as controls. At the end of the experiments the dogs were sacrificed, and identification of myocardial infarction was made with an enzyme-mapping technique in dogs with acute occlusion and with histological methods in dogs with gradual occlusion. The volume of ventricular infarction was determined with the use of an Apple II Computer and graphics tablet. After 3 months, gradual occlusion of the right coronary artery produced a 22% incidence of infarction which was significantly less (P <.01, X²) than the 67% incidence observed with 3 months of gradual circumflex occlusion. The average infarct volume produced by gradual right coronary occlusion was 0.94 + 0.69%. The average volume of left ventricular infarction in animals with circumflex acute occlusion was 15.6% + 6.6 and the incidence of infarction was 100%. With gradual occlusion of the circumflex artery for 1, 3, and 5 months, average left ventricular infarction was 2.02 ± 1.01%, 3.13 ± 1.53%, and 2.96 ± 1.35%, respectively. There were no significant differences in the amount of damage observed among the three groups with gradual occlusion, and the average incidence of infarction for these three groups was 76%. In the 1-, 3- or 5- month animals with circumflex occlusion, no additional areas of necrosis subsequent to the original damage were found, indicating that infarction is a single event in this model of gradual occlusion. These results suggest that infarct size is determined primarily by factors at the time of total occlusion and that gradual occlusion allows sufficient time for collateral growth, thereby limiting the extent of myocardial injury.     

Reperfusion effect upon ischemic myocardial injury.

Coronary artery ligation with or without reperfusion was carried out in Wistar rats to study the role of reperfusion upon ischemic cardiac muscle cell injury by using the fine structural extracellular protein tracer, horseradish peroxidase (HRP). The findings were compared with those obtained following administration of norepinephrine, a pressor and isoproterenol, a depressor catecholamine.Following the ligation of the left coronary artery that lasted for 20 min some of the collaterals in the ischemic zone were perfused by the tracer, but the number of patent capillaries decreased during a 60-min ligation. The non-homogeneous involvement of cardiac muscle cells in ischemic injury correlated well with these microcirculatory findings. Following a 60-min sustained occlusion, HRP reaction product was visualized on ribosomes and on external mitochondrial membranes of altered cardiac muscle cells. As contrasted with the findings following an identical period of permanent ischemia, after reperfusion an abrupt deterioration of the cardiac muscle cell alteration occurred with influx of plasmatic substances into altered cardiac muscle cells; also the localization of tracer was strikingly different as HRP was bound to contracted myofilaments. The similarity of the changes in the cardiac muscle cell to that seen in the catecholamine models, suggests that in addition to microcirculatory factors, direct cardiac muscle cell stimulation, possibly through release of catecholamines, may also play a role in the evolution of reperfusion injury.     

Delay of development of transmural irreversible ischaemic injury in canine myocardium

Summary During the course of experimentally induced myocardial ischaemia affected tissue initially suffers reversible ischaemic injury or, if ischaemia persists, injury of increasing severity before becoming irreversibly damaged. This state is characterized by tissue necrosis and referred to as myocardial infarction. The purpose of this study was to investigate whether it is possible to delay or perhaps even prevent the development of irreversible ischaemic injury. Ischaemia was induced by coronary artery occlusion (CAO) in canine hearts for 90 min or 24 h. The drug used for intervention was hyaluronidase. Ischaemic damage was assessed by p-NBT staining and ultrastructural evaluation of tissue biopsies. Development of irreversible ischaemic damage was prevented during 90 min of CAO. However, progression of reversible to irreversible ischaemic injury could not be prevented during 24 h of CAO. In conclusion, it is possible to prevent the development of irreversible ischaemic injury by a suitable intervention during the early stages of ischaemia in the canine heart and thus to gain time for additional intervention in the early treatment of myocardial infarction.     

Abnormal myocardial fluid retention as an early manifestation of ischemic injury.

Fifty-seven isolated, blood perfused, continuously weighed canine hearts have been utilized to study the development of abnormal myocardial fluid retention during early myocardial ischemic injury. Inflatable balloon catheters were positioned around the left anterior descending coronary arteries (LAD) of 54 hearts or the proximal left circumflex coronary arteries of three hearts for study of the following intervals of coronary occlusion: a) 10 minutes followed by 20 minutes of reflow, b) 40 minutes followed by either no reflow or by 20 minutes of reflow, and c) 60 minutes without reflow. After 60 minutes of fixed coronary occlusion, histologic and ultrastructural examination revealed mild swelling of many ischemic cardiac muscle cells in the absence of interstitial edema, cardiac weight gain, and obvious structural defects in cell membrane integrity. After 40 minutes of coronary occlusion and 20 minutes of reflow, significant cardiac weight gain occurred in association with characteristic alterations in the ischemic region, including widespread interstitial edema and focal vascular congestion and hemorrhage and swelling of cardiac muscle cells. Focal structural defects in cell membrane integrity were also noted. The development of abnormal myocardial fluid retention after 40 minutes of LAD occlusion occurred in association with a significant reduction in sodium-potassium-ATPase activity in the ischemic area, but with no significant alteration in either creatine phosphokinase or citrate synthase activity in the same region. Despite the abnormal myocardial fluid retention in these hearts, it was possible pharmacologically to vasodilate coronary vessels with adenosine and nitroglycerin infusion to maintain a consistently high coronary flow following release of the coronary occlusion after 40 minutes and to even exceed initial hyperemic flow values following release of the occlusion when adenosine and nitroglycerin infusion was delayed until 15 minutes after reflow. Thus, the data indicate that impaired cell volume regulation and interstitial fluid accumulation and focal structural defects in cell membrane integrity are early manifestations of ischemic injury followed by reflow, but fail to establish a major role for the abnormal fluid retention in altering coronary blood flow prior to the development of extensive myocardial necrosis. In contrast, fixed coronary occlusion for 60 minutes results in mild intracellular swelling but no significant interstitial edema and no obvious structural defects in cell membrane integrity.     

Abnormalities of volume regulation and membrane integrity in myocardial tissue slices after early ischemic injury in the dog: effects of mannitol, polyethylene glycol, and propranolol.

The authors used an in vitro myocardial tissue slice technique to quantitate the transmural distribution of alterations in cell volume regulation and membrane integrity following early ischemic injury and to evaluate directly the effects of therapeutic interventions in a system not subjects to influences of coronary blood flow. Left circumflex coronary occlusion was produced in 57 dogs for 30 or 60 minutes. After in vitro incubation in Krebs-Ringer-phosphate-succinate medium containing trace 14C-inulin, typical values (ml H2O/g dry weight) for control nonischemic myocardial slices were 3.68 +/- 0.07 (SEM) for total tissue water, 2.67 +/- 0.07 for inulin impermeable space, and 1.01 +/- 0.04 for inulin diffusible space. Ischemic myocardial slices exhibited an impaired response to cold shock (0 C for 60 minutes) and rewarming (37 C for 60 minutes). After 60 minutes coronary occlusion, respective increases in total tissue water, inulin-impermeable space and inulin-diffusible space of ischemic slices were 25.5 +/- 2.6%, 6.2 +/- 4.9% and 84.4 +/- 12.5% for papillary muscle, 22.2 +/- 2.1%, 10.4 +/- 4.2% and 52.5 %/- 10.3% for subendocardium and 9.1 +/- 1.5%, 7.2 +/- 2.3% and 15.8 +/- 5.5% for subepicardium. Significant but usually less marked alterations occurred after 30 minutes of coronary occlusion. Propranolol treatment in vivo (2 mg/kg) and/or in vitro (0.01 mg/ml medium) produced no significant changes in tissue water or inulin spaces of ischemic slices, compared with saline controls. Incubation in hyperosmolar mediums resulted in significant reductions in total tissue water and inulin-impermeable space with little change in inulin-diffusible space of both ischemic and control slices. Fifty milliosmolar polyethylene glycol (MW 6000) produced a greater reduction in tissue water and ultrastructural evidence of cell swelling than did either 40 or 100 milliosmolar mannitol (MW 182). The major effect of hyperosmolar incubation appeared to be a selective reduction in edema of cells with structurally intact membranes. Thus, in vitro studies, with myocardial tissue slices provide evidence of widespread alterations of membrane integrity after 30--60 minutes of in vivo coronary artery occlusion. In vitro abnormalities of cell volume regulation can be partially reversed by direct osmotic effects on myocardial cells.     

缺血预适应对心肌微循环内皮功能的保护作用

目的 探讨缺血预适应对心肌微循环内皮功能的作用。方法 复制套扎前降支冠状动脉犬模型。缺血预适应组先给予缺血5min，灌注5min，反复4次，然后缺血1h，再灌注2h；缺血再灌注组给予缺血1h后再灌注2h；两组分别于基础、缺血1h、再灌注2h采集冠状窦血对比分析一氧化氮和内皮素水平，并于再灌注2h对比分析注射乙酰胆碱前后心肌声学造影强度变化，最后用Evan氏兰和TIC双染。结果（1）正常心肌注药后声学强度增强，而缺血心肌反而下降，与再灌注组相比，预适应组缺血区心肌声学强度下降程度显著减轻（P〈0．01）；（2）两组缺血后一氧化氮水平均显著下降（P〈0．01），再灌注2h下降更为明显（P〈0．05），然而预适应组缺血1h与再灌注2h下降程度均小于再灌注组（P〈0．05）；（3）预适应组于缺血1h、再灌注2h内皮素水平比基础有所下降，再灌注组与基础比反而呈升高趋势，但未达统计学水准（P〉0．05），两组相比，预适应使缺血1h和再灌注2h的ET水平显著下降（P〈0．05）。结论 缺血预适应对心肌微循环内皮依赖性舒血管反应及一氧化氮和内皮素水平的调节具有保护效应。