Functional properties and responses to ischaemia-reperfusion in Langendorff perfused mouse heart

Despite minimal model characterisation Langendorff perfused murine hearts are increasingly employed in cardiovascular research, and particularly in studies of myocardial ischaemia and reperfusion. Reported contractility remains poor and ischaemic recoveries variable. We characterised function in C57/BL6 mouse hearts using a ventricular balloon or apicobasal displacement and assessed responses to 10-30 min global ischaemia. We examined the functional effects of pacing, ventricular balloon design, perfusate filtration, [Ca(2+)] and temperature. Contractility was high in isovolumically functioning mouse hearts (measured as the change in pressure with time (+dP/dt), 6000-7000 mmHg s(-1)) and was optimal at a heart rate of approximately 420 beats min(-1), with the vasculature sub-maximally dilated, and the cellular energy state high. Post-ischaemic recovery (after 40 min reperfusion) was related to the ischaemic duration: developed pressure recovered by 82 +/- 5 %, 73 +/- 4 %, 68 +/- 3 %, 57 +/- 2 % and 41 +/- 5 % after 10, 15, 20, 25 and 30 min ischaemia, respectively. Ventricular compliance and elastance were both reduced post-ischaemia. Post-ischaemic recoveries were lower in the apicobasal model (80 +/- 4 %, 58 +/- 7 %, 40 +/- 3 %, 32 +/- 7 % and 25 +/- 5 %) despite greater reflow and lower metabolic rate (pre-ischaemic myocardial O(2) consumption (V(O2,myo)) 127 +/- 15 vs. 198 +/- 17 microl O(2) min(-1) g(-1)), contracture, enzyme and purine efflux. Electrical pacing slowed recovery in both models, small ventricular balloons (unpressurised volumes < 50-60 microl) artificially depressed ventricular function and recovery from ischaemia, and failure to filter the perfusion fluid to < 0.45 microm depressed pre- and post-ischaemic function. With attention to these various experimental factors, the buffer perfused isovolumically contracting mouse heart is shown to be stable and highly energized, and to possess a high level of contractility. The isovolumic model is more reliable in assessing ischaemic responses than the commonly employed apicobasal model.     

Various inotropic effects of angiotensin II in post‐ischaemic rat hearts depending on ischaemic time with possible involvement of protein kinase C

Aims: The present study investigated if the inotropic effect of angiotensin II (AngII) is altered during post‐ischaemic reperfusion in hearts subjected to mild and severe ischaemia. The possible involvement of protein kinase C (PKC) in the change in the inotropic effect was also investigated. Methods: Isolated Langendorff‐perfused rat hearts were perfused under constant flow with oxygenated Krebs–Henseleit buffer and paced at 360 beats min^?1. A saline‐filled balloon catheter inserted into the left ventricle was used for measurement of contractile force. In the first series of experiments, hearts were subjected to continuous perfusion, 15‐ or 25‐min global ischaemia followed by 45‐min reperfusion. At the end of reperfusion, 0.1 μmol L^?1 AngII was infused for 5 min. In a second series of experiments, AngII was infused in hearts subjected to 25‐min ischaemia followed by 45‐min reperfusion in the absence or presence of the PKC inhibitor chelerythrine chloride (5 μmol L^?1). Results: The current study demonstrates that AngII exerts a positive inotropic effect in normoxic hearts with an increase of left ventricular developed pressure (LVDP) by 11% (P < 0.05 vs. prior to AngII infusion). In post‐ischaemic hearts subjected to 15‐min ischaemia no effect of AngII was observed. In hearts subjected to 25 min of ischaemia, however, AngII evoked a negative inotropic response with a decrease of LVDP by 18% (P < 0.05 vs. prior to AngII infusion). The negative inotropic effect of AngII was inhibited by the PKC inhibitor chelerythrine chloride. Conclusions: AngII exerts negative inotropic effect in severely injured post‐ischaemic heart, possibly through the PKC pathway.     

Cyclic fluctuations in the cardiac performance of the isolated Langendorff-perfused mouse heart: pyruvate abolishes the fluctuations and has an anti-ischaemic effect

During the development of a Langendorff preparation of isolated mouse hearts, hitherto undescribed cyclic fluctuations in left ventricular pressure and coronary flow were independently observed in three laboratories. Isolated mouse hearts were perfused with crystalloid glucose-containing Krebs-Hensleit buffer in a constant pressure model, and left ventricular pressures were measured via an intraventricular balloon catheter. After acquiring technical skill in preparing the mouse hearts, the perfusionists observed that fluctuations in cardiac performance with a cycle period lasting 5-10 min occurred shortly after initiation of perfusion. Each fluctuation cycle consisted of a phase of increase and a phase of decrease. Synchronized with the fluctuations in left ventricular pressure, increases and decreases in dP/dt max took place. Analogous fluctuations in coronary flow occurred, with onset 1-2 min later than changes in left ventricular systolic pressure. In some preparations a gradual ST-segment elevation was seen on the electrocardiogram during the systolic pressure increase phase. The amplitude of the fluctuations could be augmented by increasing the perfusion pressure, and reduced, but not abolished, by lowering the pressure. Changes in buffer calcium, magnesium, or sodium concentration did not alter the fluctuations, nor did any change of anaesthetics, mouse strain, or left ventricular drainage. Altering the perfusion mode from constant pressure to constant flow did not prevent the occurrence of the cyclic fluctuations. The hearts became stable and the fluctuations disappeared when the buffer was supplemented with 2 mm pyruvate. In the present study, pyruvate given throughout stabilization and reperfusion also markedly attenuated the ischaemic insult, as evidenced by the delayed ischaemic contracture and a reduced magnitude of ischaemic contracture. A cardioprotective effect was only visible at early reperfusion, did not affect the final functional recovery. In conclusion, a phenomenon of cyclic fluctuations in left ventricular pressure followed by fluctuations in coronary flow was observed in isolated mouse hearts. These could be abolished by adding 2 mm pyruvate to the perfusion buffer. Pyruvate in the buffer also markedly attenuated the post-ischaemic deterioration of cardiac performance seen in this mouse model.     

Relationship between ischaemic time and ischaemia/reperfusion injury in isolated Langendorff‐perfused mouse hearts

Myocardial functional recovery and creatine kinase (CK) release following various periods of ischaemia were investigated in isolated mouse hearts. The hearts were perfused in the Langendorff mode with pyruvate‐containing Krebs–Hensleit (KH) buffer under a constant perfusion pressure of 80 mmHg, and were subjected to either continuous perfusion or to 5, 15, 20, 25, 30, 45 or 60 min of global ischaemia followed by 45 min of reperfusion. In hearts subjected to ischaemic periods of 5, 15 or 20 min, there was a transient reduction in the left ventricular (LV) dP/dt max during the early phase of reperfusion, while the recovery at the end of reperfusion reached a level similar to that in hearts subjected to continuous perfusion. In hearts subjected to longer ischaemic periods, i.e. 25, 30, 45 or 60 min, the decrease in the cardiac performance was more pronounced and persistent, with significantly lower recovery in LV dP/dt max and higher LV end diastolic pressure (LVEDP) at the end of reperfusion than in the non‐ischaemic hearts. There were no significant differences in the recoveries in coronary flow or in heart rate (HR) between groups. Similarly to the functional recovery, the release of CK showed a clear ischaemic length‐related increase. In conclusion, the Langendorff‐perfused isolated mouse heart could be a valuable model for studies of myocardial ischaemia/reperfusion injury. Future studies using gene‐targeted mice would add valuable knowledge to the understanding of myocardial ischaemia/reperfusion injury.     

Cyclic fluctuations in the cardiac performance of the isolated Langendorff‐perfused mouse heart: pyruvate abolishes the fluctuations and has an anti‐ischaemic effect

During the development of a Langendorff preparation of isolated mouse hearts, hitherto undescribed cyclic fluctuations in left ventricular pressure and coronary flow were independently observed in three laboratories. Isolated mouse hearts were perfused with crystalloid glucose‐containing Krebs–Hensleit buffer in a constant pressure model, and left ventricular pressures were measured via an intraventricular balloon catheter. After acquiring technical skill in preparing the mouse hearts, the perfusionists observed that fluctuations in cardiac performance with a cycle period lasting 5–10 min occurred shortly after initiation of perfusion. Each fluctuation cycle consisted of a phase of increase and a phase of decrease. Synchronized with the fluctuations in left ventricular pressure, increases and decreases in dP/dt max took place. Analogous fluctuations in coronary flow occurred, with onset 1–2 min later than changes in left ventricular systolic pressure. In some preparations a gradual ST‐segment elevation was seen on the electrocardiogram during the systolic pressure increase phase. The amplitude of the fluctuations could be augmented by increasing the perfusion pressure, and reduced, but not abolished, by lowering the pressure. Changes in buffer calcium, magnesium, or sodium concentration did not alter the fluctuations, nor did any change of anaesthetics, mouse strain, or left ventricular drainage. Altering the perfusion mode from constant pressure to constant flow did not prevent the occurrence of the cyclic fluctuations. The hearts became stable and the fluctuations disappeared when the buffer was supplemented with 2 mm pyruvate. In the present study, pyruvate given throughout stabilization and reperfusion also markedly attenuated the ischaemic insult, as evidenced by the delayed ischaemic contracture and a reduced magnitude of ischaemic contracture. A cardioprotective effect was only visible at early reperfusion, did not affect the final functional recovery. In conclusion, a phenomenon of cyclic fluctuations in left ventricular pressure followed by fluctuations in coronary flow was observed in isolated mouse hearts. These could be abolished by adding 2 mm pyruvate to the perfusion buffer. Pyruvate in the buffer also markedly attenuated the post‐ischaemic deterioration of cardiac performance seen in this mouse model.     

Relationship between ischaemic time and ischaemia/reperfusion injury in isolated Langendorff-perfused mouse hearts

Myocardial functional recovery and creatine kinase (CK) release following various periods of ischaemia were investigated in isolated mouse hearts. The hearts were perfused in the Langendorff mode with pyruvate-containing Krebs-Hensleit (KH) buffer under a constant perfusion pressure of 80 mmHg, and were subjected to either continuous perfusion or to 5, 15, 20, 25, 30, 45 or 60 min of global ischaemia followed by 45 min of reperfusion. In hearts subjected to ischaemic periods of 5, 15 or 20 min, there was a transient reduction in the left ventricular (LV) dP/dt max during the early phase of reperfusion, while the recovery at the end of reperfusion reached a level similar to that in hearts subjected to continuous perfusion. In hearts subjected to longer ischaemic periods, i.e. 25, 30, 45 or 60 min, the decrease in the cardiac performance was more pronounced and persistent, with significantly lower recovery in LV dP/dt max and higher LV end diastolic pressure (LVEDP) at the end of reperfusion than in the non-ischaemic hearts. There were no significant differences in the recoveries in coronary flow or in heart rate (HR) between groups. Similarly to the functional recovery, the release of CK showed a clear ischaemic length-related increase. In conclusion, the Langendorff-perfused isolated mouse heart could be a valuable model for studies of myocardial ischaemia/reperfusion injury. Future studies using gene-targeted mice would add valuable knowledge to the understanding of myocardial ischaemia/reperfusion injury.     

甘氨酰谷氨酰胺在大鼠离体心脏缺血/再灌注损伤中的保护作用研究

目的： 研究甘氨酰谷氨酰胺对缺血再灌注大鼠离体心脏的保护作用。方法：应用Langendorff离体心脏灌注系统建立心肌缺血再灌注模型。30只SD雄性大鼠随机分为正常对照组(control)、甘氨酰谷氨酰胺对照组(Gly-Gln)、缺血再灌注组(I/R)、缺血/再灌注+甘氨酰谷氨酰胺组(I/R+ Gly-Gln)。I/R组及I/R+ Gly-Gln组分别灌注30 min后,全心停灌20 min,再灌注40 min,I/R+ Gly-Gln组于再灌注时在灌流液中加入Gly-Gln;正常对照组连续灌流90 min,Gly-Gln对照组灌流液中加入Gly-Gln。记录各组灌注时,左室舒张末压(LVEDP)、左室发展压(LVDP)、左室压力最大变化速率(±dp/dtmax)、心率(HR)及心肌细胞单相动作电位(MAP);同时在相应的时点分别测定冠脉流出液中的乳酸脱氢酶（LDH)、肌酸激酶(CK)活性。结果：离体大鼠心脏缺血20min,再灌注40 min,导致严重的心功能抑制,表现为LVEDP升高,LVDP、±dp/dtmax降低;再灌注液中加入Gly-Gln后,LVEDP降低,LVDP、±dp/dtmax明显升高（P<0.01)。I/R+ Gly-Gln组冠脉流出液中LDH、CK活性明显低于I/R组(均P<0.01)。结论： Gly-Gln能有效减轻缺血再灌注引起的左室功能下降,减少心肌细胞LDH、CK的释出,表明Gly-Gln对缺血再灌注损伤的大鼠离体心脏具有保护作用。     

Cardiac function in open-chest dogs after left to right ventricular shunting and right coronary artery occlusion

Patients with acquired ventricular septal defect (VSD) after myocardial infarction have a particularly bad prognosis if right ventricular function is severely impaired. The significance of an ischaemic right ventricular free wall on cardiac function during interventricular shunting was examined in open-chest dogs. An external interventricular shunt could be opened and closed at will, and by occlusion of the right coronary artery (RCA), a part of the right ventricular free wall was rendered ischaemic. Aortic flow decreased by 8 +/- 2% when the shunt was opened in the presence of a normal right ventricle, and by 16 +/- 2% (difference: P less than 0.05) in the presence of right ventricular ischaemia. Aortic flow fell by 19 +/- 3% when the RCA was occluded. Right ventricular dyskinesia was demonstrated after occlusion of RCA, by recording segment lengths in the right ventricular free wall. The dyskinesia was aggravated when the shunt was opened. The left ventricle exerted a 'negative' work on the ischaemic right ventricular free wall. Retention of blood in the right ventricle, with a subsequent decline in left ventricular filling and an almost unchanged interventricular shunting of blood, explain why aortic flow fell more when the shunt was opened in the presence of right ventricular ischaemia.     

Long-term structural and functional consequences of cardiac ischaemia-reperfusion injury in vivo in mice

The short-term (<24 h) consequences of oxidative stress induced by ischaemia-reperfusion (IR) have been studied extensively in the mouse heart. However, much less is known about the long-term effects inflicted by a brief ischaemic period on the murine heart. We therefore examined the structural and functional consequences of a 30 min ischaemic period after 2 and 8 weeks of reperfusion and compared these to the effects induced by permanent occlusion of the left anterior descending coronary artery (LAD). The latter procedure resulted in transmural myocardial infarcts of about 52% of the left ventricle. In contrast, the single 30 min ischaemic period led to infarct sizes of about 13% of the left ventricle (range, 4-23%) at 2 and 8 weeks after reperfusion. Maximal cardiac contractility responses (+dP/dt) to dobutamine infusion and volume loading were depressed at 2, but not at 8 weeks after IR. The restoration of cardiac contractility at 8 weeks after IR was associated with a significant 20% enlargement of the end-diastolic volume and 16% increase of the left ventricular wall thickness. These changes in cardiac geometry were less pronounced at 2 weeks after IR. Histological examination revealed that the IR injury was associated with prominent calcification. At 2 and at 8 weeks after IR, 25 +/- 5 and 38 +/- 5% of the injured area was calcified as observed in 69 and 73% of the animals, respectively. After permanent occlusion of the LAD, calcification was not observed and healing of the affected area was characterized by thinning and dilatation of the infarcted myocardium. These data indicate that, in mice, a single 30 min period of ischaemia reduced ventricular contractility up to at least 2 weeks after reperfusion. However, 8 weeks after IR, cardiac function was restored by eccentric hypertrophy associated with calcification of the injured ventricular wall.     

Left ventricular mechanoreceptors: a haemodynamic study

1. To study the function of the left ventricular mechanoreceptors, a working left ventricle preparation was devised in dogs which permitted control of pressure and flow of the isolated perfused coronary circulation and of the flow of the isolated, separately perfused systemic circulation. The systemic circulation was perfused at a constant rate so that changes in systemic pressure reflected changes in systemic resistance.2. Increases in myocardial contractility produced by injection of catecholamines into the isolated, perfused coronary circulation produced a fall in the pressure (resistance) of the isolated, separately perfused (at a constant rate) systemic circulation.3. Completeness of isolation of the coronary and systemic circulations was shown by the marked difference in appearance times between the reflex hypotensive responses from catecholamine injections into the isolated coronary circulation and the direct hypertensive response from a similar injection when the circulations were connected as well as by the marked difference between the pressure pulses recorded simultaneously on both sides of the aortic balloon separating the two circulations.4. Myocardial beta receptor blockade produced by injection of propranolol into the isolated coronary circulation abolished or attenuated the changes in left ventricular myocardial contractility as well as the subsequent hypotensive responses following the similar injection of catecholamines.5. Electrical stimulation of a sympathetic nerve innervating the heart resulted in increases in left ventricular myocardial contractility and subsequent systemic hypotensive responses indistinguishable from those following injection of catecholamines.6. That distortion of the mechano- or stretch receptors in the left ventricular myocardium was the cause of the hypotensive responses was demonstrated by increasing left ventricular myocardial contractility by mechanically obstructing the left ventricular outflow which produced hypotensive responses similar to those following the injection of catecholamines or nerve stimulation.7. Bilateral high cervical vagotomy abolished the hypotensive responses following injection of catecholamines into the isolated coronary circulation or following left ventricular outflow obstruction in all but one instance, indicating the importance of vagal fibres to the afferent arm of the reflex.8. It is suggested that the left ventricular mechanoreceptors function normally to reduce the peripheral resistance in order to prepare the systemic circulation to receive the left ventricular output and, especially during exercise, to prepare the systemic circulation to receive the augmented cardiac output with a minimum alteration in the systemic blood pressure and to distribute this augmented output preferentially to the skeletal muscles.     

Myoglobin function in the isolated fluorocarbon-perfused dog heart

An isolated dog heart preparation perfused with hemoglobin-free fluorocarbon suspension has been developed to study the role of myoglobin in myocardial function. The coronary vasculature was perfused at constant flow, with oxygen consumption determined from arteriovenous PO2 differences. Muscle function was assessed by measurement of pressures generated in a latex balloon placed in the left ventricle. The perfusate consisted of 20% perfluorotributylamine and 80% Ringer's lactate with 16 mM glucose. Steady-state oxygen consumption decreased from 0.30 to 0.11 ml/min per gram dry weight left ventricle, as perfusate PO2 decreased from 690 to 150 mmHg. Left ventricular pressure generation and oxygen consumption were determined before and after addition of 8 mM sodium nitrite, which changed functional ferrous myoglobin to high-spin ferric myoglobin. Over the range of perfusate PO2 studied, nitrite addition did not alter mechanical performance or myocardial oxygen consumption. These data suggest that those conditions necessary for substantial myoglobin-facilitated diffusion of oxygen in the myocardium are not present in the isolated fluorocarbon-perfused dog heart.     

99-m technetium (Dupont Cardiolite) investigations in postinfarction patients with Holter-checked silent ischaemia.

Sixteen middle-aged, normotensive, slightly overweight male patients with previous myocardial infarction were studied during Holter-checked silent myocardial ischaemia. As reference, stress and late 201-T1 scintigraphy served for comparison with Cardiolite-MIBI silent ischaemic perfusion scan, both carried out in planar mode. The circumferential profiles differed in 9 cases, on region of interest basis the segment number difference was 10, but the late distribution segment number was near to both ischaemic numbers. The quantitative scores were distinctive (ratio 133-128/103) indicating the silent ischaemia appeared in the peri-infarct area. The silent ischaemic MIBI and stress 201-T1 ischaemic score difference was reduced by means of repeated SPECT investigation. With gated radionuclide ventriculography there was -4.3% difference between the left ventricular ejection fractions, measured with first pass MIBI technique during silent ischaemia and afterwards in basal state. The impairment of the left ventricular function was reflected on the stroke pattern of our Holter-based radiocyclogram, as well. Taking the 43.7-48.0 = -4.3% "ischaemic shift" into consideration it was a close correlation (r = 0.90) between the two kinds of ejection fraction determination. The major rhythm failures (occurring during the 24 h Holter monitoring) decreased to a higher degree the left ventricular ejection fraction than silent ischaemia or silent ischaemia and minor rhythm failure together (38-42-50%).     

Endogenous nitric oxide attenuates hypoxic vasoconstriction of small pulmonary arteries and veins in anaesthetized cats

Ischaemic preconditioning has cardioprotective effects. Reactive oxygen species may be possible mediators. The present study investigated whether low doses of exogenous hydrogen peroxide could mimic preconditioning in isolated, Langendorff-perfused rat hearts. Hearts were subjected to two episodes of 3 min global ischaemia and 5 min reperfusion (n = 17), or were given 10 (n=15), 20 (n=10), 30 (n=20), 40 (n=18), 80 (n=17) or 160 μM (n=10) hydrogen peroxide for 10 min, followed by 10 min recovery, before 25 min global ischaemia and 60 min reperfusion, and compared with ischaemic controls of matching perfusion time (n=17 and n=23). Cardiac performance was assessed by heart rate, left ventricular systolic, end-diastolic and developed pressures, and coronary flow. Severe reperfusion arrhythmias occurred frequently in control hearts, and was attenuated by ischaemic preconditioning. All hearts pretreated with 160 μM hydrogen peroxide had severe arrhythmias throughout reperfusion, while these were not seen in any heart perfused with 20 μM hydrogen peroxide (P< 0.01 compared to controls). Ischaemia and reperfusion induced a minor decrease in heart rate, left ventricular systolic and developed pressures, and increased end-diastolic pressure. Ischaemic preconditioning attenuated the decrease of heart rate and the increase of end-diastolic pressure, and increased coronary flow, while hydrogen peroxide did not significantly attenuate these changes. In conclusion, a low dose of exogenous hydrogen peroxide before global ischaemia inhibited severe reperfusion arrhythmias, but had no other protective effects. The present work does not suggest that reactive oxygen species are important mediators of the preconditioning effects on stunning and arrhythmias in the rat heart.     

Myocardial contracture and accumulation of mitochondrial calcium in ischemic rabbit heart

The relationship between myocardial contracture and cell calcium was studied in electrically paced, isolated perfused rabbit hearts. Isovolumic left ventricular dP/dt and end-diastolic pressure were utilized as indexes of contractility and ventricular stiffness. After 60 min of low flow (ischemia) without or with reperfusion at high flow for 10 min, calcium was measured in the mitochondrial fraction and used as an indicator of intracellular calcium. Low flow led to ventricular standstill and contracture, and reperfusion produced partial mechanical recovery with end-diastolic pressure remaining markedly elevated. Nifedipine (10(-7) M), an antagonist of myocardial calcium uptake, prevented contracture and permitted nearly complete mechanical recovery without elevation in diastolic pressure. Increases in mitochondrial calcium paralleled the severity of contracture and the lack of diastolic relaxation after reperfusion. Mitochondrial calcium did not increase in hearts protected by nifedipine. Results demonstrate a close relationship between mechanical changes induced by ischemia and accumulation of intracellular calcium.     

Various inotropic effects of angiotensin II in post-ischaemic rat hearts depending on ischaemic time with possible involvement of protein kinase C

AIMS: The present study investigated if the inotropic effect of angiotensin II (AngII) is altered during post-ischaemic reperfusion in hearts subjected to mild and severe ischaemia. The possible involvement of protein kinase C (PKC) in the change in the inotropic effect was also investigated. METHODS: Isolated Langendorff-perfused rat hearts were perfused under constant flow with oxygenated Krebs-Henseleit buffer and paced at 360 beats min(-1). A saline-filled balloon catheter inserted into the left ventricle was used for measurement of contractile force. In the first series of experiments, hearts were subjected to continuous perfusion, 15- or 25-min global ischaemia followed by 45-min reperfusion. At the end of reperfusion, 0.1 micromol L(-1) AngII was infused for 5 min. In a second series of experiments, AngII was infused in hearts subjected to 25-min ischaemia followed by 45-min reperfusion in the absence or presence of the PKC inhibitor chelerythrine chloride (5 micromol L(-1)). RESULTS: The current study demonstrates that AngII exerts a positive inotropic effect in normoxic hearts with an increase of left ventricular developed pressure (LVDP) by 11% (P<0.05 vs. prior to AngII infusion). In post-ischaemic hearts subjected to 15-min ischaemia no effect of AngII was observed. In hearts subjected to 25 min of ischaemia, however, AngII evoked a negative inotropic response with a decrease of LVDP by 18% (P<0.05 vs. prior to AngII infusion). The negative inotropic effect of AngII was inhibited by the PKC inhibitor chelerythrine chloride. CONCLUSIONS: AngII exerts negative inotropic effect in severely injured post-ischaemic heart, possibly through the PKC pathway.     

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.     

The influence of coronary pressure and coronary flow on intracoronary blood volume and geometry of the left ventricle

Summary Intracoronary blood volume in relation to coronary perfusion pressure was estimated in dog hearts in situ with cannulated left coronary arteries. Electromagnetically measured inflow into coronary arteries times mean transit time, obtained by a dye dilution technique determined the intracoronary blood volume. Within the range from 70 and 170 mm Hg coronary perfusion pressure the mean value of intracoronary blood volume increases from 11.0 to 17.8 ml per 100 g wet weight; an increase of about 62%. The mycocardial wall at 70 mm Hg consists of 10.4% intracoronary blood and at 170 mm Hg of 15.1%. A significant increase in intracoronary blood volume is seen with increasing coronary perfusion pressure at constant coronary flow.With increasing coronary perfusion pressure the outer volume of the heart and the volume of the myocardial wall increases while the inner volume of the left ventricle decreases in blood perfused dog hearts in situ and in isolated cat hearts. The mean radius of the left ventricle is not changed by the coronary perfusion pressure. This change in the geometry of the left ventricle influences the pressurevolume relation of the heart and can explain the effect of coronary perfusion pressure on the performance of the heart.     

Leakage of cytoplasmic enzymes from rat heart by the stress of cardiac beating after increase in cell membrane fragility by anoxia

The effects of spontaneous beating after anoxia and the pumping stress induced by a left ventricular balloon on the leakage of myocardial enzymes from the isolated perfused rat heart were investigated. Beating of the heart was arrested by perfusion with high-K⁺ medium. When the beating was arrested during reoxygenation after anoxia, the leakage of lactate dehydrogenase (LDH) was significantly lower than during reoxygenation with spontaneous cardiac beating. After changing from K⁺ arrest to spontaneous beating by perfusion with low-K⁺ medium during reoxygenation, the leakage of LDH increased markedly. Imposition of left ventricular wall stress on the K⁺-arrested heart by repetitive passive distension during aerobic perfusion and after 20 min and 60 min of anoxia caused LDH leakages of 1.0, 4.6 and 21.0 units/g in 30 min, respectively. Under this mechanical stress, the release of LDH as a percentage of its total myocardial activity coincided well with that of cytoplasmic aspartate aminotransferase (AST), while the percentage release of mitochondrial AST was much less. These results appeared to indicate that the leakage of cytoplasmic enzymes during reoxygenation is accelerated by cardiac beating because of fragility of the cell membranes developing during the preceding anoxia.     

The effect of bone marrow‐ and adipose tissue‐derived mesenchymal stem cell transplantation on myocardial remodelling in the rat model of ischaemic heart failure

This study aimed to investigate the effect of bone marrow‐ and adipose tissue‐derived mesenchymal stem cell (BM‐MSC and AD‐MSC respectively) transplantation on left ventricular function and infarct area (IA) in the rat model of ischaemic heart failure. In anaesthetized Wistar rats, the left coronary artery (LCA) was occluded for 40 min with subsequent reperfusion for 7 days. Seven days following surgery, the animals with LCA occlusion/reperfusion were randomized into three groups: (i) Controls received intramyocardial injection of vehicle at three different locations within the peri‐infarct zone, (ii) BM‐MSC: cells were injected in the same way as in previous group (10⁶), (iii) AD‐MSC: using the same protocol as used in the BM‐MSC group. In addition there was also a sham‐treated group that had no injection. Two weeks following MSC transplantation, the hearts were isolated and perfused according to the Langendorff method followed by 30‐min global ischaemia and 90‐min reperfusion. After this IA was determined histologically. During Langendorff perfusion initial and postischaemic LV functions were the same in all groups although LV pressure at the 10th minute of reperfusion was higher in the AD‐MSC group compared to controls. However, LV pressure during 30‐min global ischaemia was significantly higher in BM‐MSC as compared to controls and AD‐MSC. The sham treated animals showed the same results as those seen with BM‐MSC. Thus, BM‐MSC transplantation, in contrast to transplantation of AD‐MSC, resulted in better preservation of the LV ability to contract during ischaemia. Furthermore, IA was significantly smaller in BM‐MSC group as compared to the controls and the AD‐MSC groups. Thus this study has demonstrated that treatment with BM‐MSC both ameliorates LV function and reduces histological scar size.     

Reversal of the no reflow phenomenon in globally ischemic rat hearts by ventricular dilation

Changes in the contracture and stiffness of ventricular walls during ischemia and their effect on vascular reperfusion were studied in isolated rat hearts. Global ischemia was induced by stopping the flow of oxygenated perfusate for 60 min. Contracture pressures generated against water-filled left ventricular balloons maintained at diastolic volume increased between 8 and 25 min of ischemia and declined thereafter. On the other hand, left ventricular wall stiffness, estimated from the pressure required to periodically inflate otherwise uninflated balloons to diastolic volume, increased rapidly between 20 and 30 min of ischemia, and more slowly thereafter. Inflation of balloons following 30 or more min of ischemia caused significant reductions in left ventricular wall stiffness. Similar brief inflation after 60 min of ischemia allowed aqueous sodium fluorescein to perfuse the subendocardial half of the left ventricular wall which was otherwise not accessible to reperfusion. This reversal of the no reflow phenomenon was accompanied by a reduction in myocardial wall stiffness, stretching of myocytes and increased patency of myocardial capillaries.