Inability of methylprednisolone sodium succinate to decrease infarct size or preserve enzyme activity measured 24 hours after coronary occlusion in the dog

Enhanced effect of combining human cardiac stem cells and bone marrow mesenchymal stem cells to reduce infarct size and to restore cardiac function after myocardial infarction

BACKGROUND

Because mesenchymal stem cells (MSCs) induce proliferation and differentiation of c-kit(+) cardiac stem cells (CSCs) in vivo and in vitro, we hypothesized that combining human (h) MSCs with c-kit(+) hCSCs produces greater infarct size reduction compared with either cell administered alone after myocardial infarction (MI).

METHODS AND RESULTS

Yorkshire swine underwent balloon occlusion of the left anterior descending coronary artery followed by reperfusion and were immunosuppressed after MI with cyclosporine and methylprednisolone. Intramyocardial combination hCSCs/hMSCs (1 million cells/200 million cells, n=5), hCSCs alone (1 million cells, n=5), hMSCs alone (200 million cells, n=5), or placebo (phosphate-buffered saline; n=5) was injected into the infarct border zones at 14 days after MI. Phenotypic response to cell therapy was assessed by cardiac magnetic resonance imaging and micromanometer conductance catheterization hemodynamics. Although each cell therapy group had reduced MI size relative to placebo (P<0.05), the MI size reduction was 2-fold greater in combination versus either cell therapy alone (P<0.05). Accompanying enhanced MI size reduction were substantial improvement in left ventricular chamber compliance (end-diastolic pressure-volume relationship; P<0.01) and contractility (preload recruitable stroke work and dP/dtmax; P<0.05) in combination-treated swine. Ejection fraction was restored to baseline in cell-treated pigs, whereas placebo pigs had persistently depressed left ventricular function (P<0.05). Immunohistochemistry showed 7-fold enhanced engraftment of stem cells in the combination therapy group versus either cell type alone (P<0.001).

CONCLUSIONS

Combining hMSCs and hCSCs as a cell therapeutic enhances scar size reduction and restores diastolic and systolic function toward normal after MI. Taken together, these findings illustrate important biological interactions between c-kit(+) CSCs and MSCs that enhance cell-based therapeutic responses.

Complement inhibitors in myocardial ischemia/reperfusion injury

Myocardial ischemia/reperfusion injury is accompanied by an inflammatory response contributing to reversible and irreversible changes in tissue viability and organ function. Endothelial and leukocyte responses are involved in tissue injury, orchestrated primarily by the complement cascade. Anaphylatoxins, and assembly of the membrane attack complex contribute directly and indirectly to further tissue damage. Tissue salvage can be achieved by depletion of complement components, thus making evident a contributory role for the complement cascade in ischemia/reperfusion injury. The complexity of the complement cascade provides numerous sites as potential targets for therapeutic interventions designed to modulate the complement response to injury. The latter is exemplified by the ability of a soluble form of complement receptor 1 (sCR1) to decrease infarct size in in vivo models of ischemia/reperfusion injury as well as prevent myocyte and vascular injury and organ dysfunction by interdicting assembly of the membrane attack complex. Effective inhibitors of complement are not limited to newly developed compounds or solubilized forms of endogenous regulators of complement activation. Therapeutic agents in common use, such as heparin and related non-anticoagulant glycosaminoglycans, are known to inhibit the complement activation in vitro as well as in vivo and may prove useful as cytoprotective agents.

Steroid-induced enhancement of functional recovery of postischemic, reperfused myocardium in conscious dogs

The effects of methylprednisolone sodium succinate (20 mg/kg, intravenously administered) on the time course of functional recovery of myocardium following a 15-minute coronary artery occlusion period and subsequent 5 hour reperfusion period were studied in chronically instrumented, conscious dogs. In comparison to a control group, animals receiving methylprednisolone 90 minutes prior to coronary occlusion demonstrated less depression of regional segment shortening following 15 minutes of reperfusion (52 +/- 13% vs control levels of 23 +/- 7% of preocclusion values) and improved recovery at 5 hours postreperfusion (106 +/- 6% vs control levels of 54 +/- 4% of preocclusion values). In animals receiving methylprednisolone immediately prior to reperfusion, there was also similar recovery of segment shortening at 5 hours (97 +/- 3%). In contrast, dogs receiving methylprednisolone 15 minutes after the onset of reperfusion or sodium succinate (5.5 mg/kg, intravenously administered) 90 minutes prior to occlusion demonstrated no improvement in recovery of function. Experiments in dogs not subjected to coronary occlusion documented that methylprednisolone sodium succinate lacked inotropic and vasodilator properties. The results suggest that methylprednisolone administered prior to or during coronary artery occlusion but not after reperfusion enhances the functional recovery of hypokinetic, postischemic, reperfused myocardium. These effects are unrelated to any direct hemodynamic action of steroids or to the sodium succinate salt.

Effects of alloxan-induced diabetes on ischemia-reperfusion injury in rabbit hearts

Hearts from rabbits with 8-16 weeks of alloxan-diabetes were compared with hearts from normal rabbits to determine whether diabetic myocardium is more sensitive to ischemic injury. In isolated buffer-perfused hearts, left ventricular developed pressure, diastolic pressure, time to peak pressure (TTPP), time to half-maximal relaxation (RT1/2), and positive and negative dP/dt were measured during generation of left ventricular filling curves before and after 90 minutes of low-flow ischemia. Hearts from diabetic rabbits (blood glucose, 384 +/- 28 mg/dl, mean +/- 95% confidence limits) had left ventricular developed and diastolic pressures similar to normal hearts but exhibited significant increases in TTPP and RT1/2 with decreased positive and negative dP/dt. Left ventricular chamber volume relative to heart mass was greater in diabetic than in normal hearts. Recovery of developed pressure after ischemia was similar in normal (41 +/- 16%) and diabetic hearts (47 +/- 13%). In diabetic hearts during recovery from ischemia, TTPP and R1/2 remained increased compared with normal hearts, with positive and negative dP/dt decreased compared with normal hearts, in proportion to the preischemic differences. After ischemia, high-energy phosphates were depleted to the same extent in normal and diabetic rabbits. In coronary ligation experiments, histochemically determined infarct size in diabetic rabbits after 30 minutes occlusion and 24 hours reperfusion was similar to that in normal rabbits when adjusted for a significantly smaller heart weight and a correspondingly smaller anatomic risk region in the diabetic animals. Thus, despite characteristic abnormalities of mechanical function in diabetic hearts, the severity of injury after ischemia with reperfusion was normal for diabetic hearts.

Steroid administration after myocardial infarction promotes early infarct expansion. A study in the rat

Whether steroids lead to thinner scars and larger aneurysms by delaying collagen deposition or worsening infarct expansion before significant collagen deposition begins is unknown. Rats underwent either transmural infarction by left coronary ligation or sham operation. Both infarct and sham rats were randomized to methylprednisolone 50 mg/kg i.p. X 4 or saline treatment within 24 h after operation. Sacrifice occurred before (3 d) or after (7 d) collagen deposition typically begins. Despite similar infarct size, infarct wall thickness was 1.35 +/- 0.08 mm in the saline and 0.99 +/- 0.12 mm in the methylprednisolone group (P less than 0.001) at 3 d. This decrease in wall thickness was explained by a decrease in the number of myocytes across the infarct wall (r = 0.99; P less than 0.001), suggesting that steroids promote myocyte slippage. Furthermore, methylprednisolone caused no further infarct thinning or cavity dilatation beyond 3 d. Thus, high-dose methylprednisolone given within 24 h after transmural infarction worsens infarct expansion before collagen is laid down by promoting the slippage of necrotic myocytes.

Effects of early reperfusion in acute myocardial infarction on arrhythmias induced by programmed stimulation: a prospective, randomized study

This study compares inducibility of ventricular tachyarrhythmias by programmed electrical stimulation of the heart in patients with myocardial infarction with and without reperfusion after streptokinase therapy. Sixty-two consecutive patients admitted with an acute myocardial infarction were randomized to either combined intravenous and intracoronary streptokinase (streptokinase group) or to standard coronary care unit treatment (control group). Thirty-six of the 62 patients (21 patients from the streptokinase and 15 from the control group) with a first myocardial infarction were studied by programmed ventricular stimulation after a mean of 26 +/- 14 days. No patient had a history of antiarrhythmic drug use or documentation of a ventricular arrhythmia before the initial admission. A sustained ventricular arrhythmia was induced in 10 (48%) of the 21 patients randomized to streptokinase therapy and in all 15 (100%) control patients (p less than 0.001). Sustained monomorphic ventricular tachycardia was induced in 6 (29%) and 10 (67%) patients, respectively (p less than 0.05). To terminate an induced arrhythmia, direct current countershock was required in 33% of patients in the streptokinase group and 73% of patients in the control group (p less than 0.02). Seventeen of the 21 patients treated with streptokinase and no control patient had evidence of early reperfusion 200 +/- 70 minutes after the onset of pain. In comparison with patients without early reperfusion, patients in the reperfused group had a lower maximal serum creatine kinase value (p less than 0.01), a shorter time to peak creatine kinase value (p less than 0.001) and a higher angiographic left ventricular ejection fraction (62 versus 45%, p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Infarct size reduction: a review of the clinical trials

The most important finding to emerge from this review of experimental and clinical studies is that the earlier therapy is begun after the onset of symptoms of acute MI, the greater the potential for reduction of infarct size and possibly mortality. It is difficult to define a precise time after which therapy would not have an effect, since the clinical trials for each drug group vary significantly in respect to time of therapy initiation. In experimental studies, major salvage of ischemic myocardium occurs when the drug is given within two hours of coronary artery occlusion. If drug therapy is begun four to six hours postocclusion, then only minor or no reductions in infarct size will occur. The ability of any drug or intervention to reduce infarct size in humans would be optimized if therapy were begun less than four hours of onset of symptoms. With the realization of the wavefront phenomenon and the potential salvage of myocardium at risk with reperfusion, the introduction of reperfusion in the clinical setting with thrombolytic agents or other procedures becomes highly desirable. Clot-selective thrombolytic agents, such as tissue plasminogen activator, diminish the adverse effects and high costs of intracoronary thrombolytic therapy or PTCA. Consequently, it is probable that the initial procedure of choice would be the use of clot-selective thrombolytic therapy. Thrombolytic therapy only lyses thrombi and does not affect the underlying causes of the coronary artery occlusion. Therefore, therapy to reduce the chances of reinfarction and death must also be initiated. Percutaneous transluminal coronary angioplasty, in selected patients, should reduce the reocclusion rate. Beta-adrenoceptor blocking agents appear to be an excellent therapy for reducing mortality when administered chronically; these agents reduce myocardial oxygen consumption and reverse the imbalance between oxygen supply and oxygen demand caused by activation of the sympathetic nervous system and actions of catecholamines. Since thrombus formation has occurred at least once in patients who survive an MI, it is probable that the conditions for thrombus formation still exist. Therefore, institution of antiplatelet aggregating drugs, such as aspirin, would seem to be an appropriate prophylactic regimen. Beta blockers and possibly nitroglycerin have desirable effects when thrombolysis is unavailable. The efficacy of calcium-channel blocking agents on reduction of infarct size appears to be limited, although in the setting of stable and unstable angina postinfarction, these agents can play an important role.(ABSTRACT TRUNCATED AT 400 WORDS)

Failure of nifedipine and reperfusion to reduce infarct size relative to region at risk as measured by NADH fluorophotography

In this report we describe a new technique for the measurement of region at risk after coronary artery ligation in the rabbit by NADH fluorophotography. We also describe the application of this technique to a study of nifedipine combined with reperfusion in experimental myocardial infarction. In 16 untreated rabbits the epicardial surface area of NADH fluorescence immediately after coronary ligation correlated with infarct size at 24 hr after coronary occlusion, as measured by nitro blue tetrazolium staining (r = .84, p less than .001). In 24 rabbits we studied the effect of nifedipine administered immediately after coronary ligation and combined with reperfusion at 1 hr after occlusion. Nifedipine had no significant effect on region at risk or infarct size.

Effects of steroid treatment on release of cardiac myosin light chain II in acute myocardial infarction in dogs

The effect of methylprednisolone sodium succinate (MP) on release of myosin light chain II (LCII) from the myocardium was studied in experimental myocardial infarction (MI). Acute MI was produced in conscious, closed-chest dogs by ligating the left anterior descending coronary artery beyond the first diagonal branch. MP, 30 mg/kg, was administered intravenously just before and 24 hours after MI. After MI, LCII levels in the serum were determined serially up to 240 hours. MI size was determined histologically 10 days after MI. In the MP group, LCII levels in the serum within 72 hours were lower than in the control, and cumulative LCII release for 3 days decreased from 530 +/- 159 to 310 +/- 101 ng/ml (mean +/- standard deviation) (p less than 0.001). However, the peak LCII level appeared later (control vs MP, 63 +/- 27 vs 122 +/- 25 hours, p less than 0.001), and the peak LCII level and cumulative LCII release for 10 days were not decreased by MP treatment. MI size also was not reduced by MP (11.0 +/- 4.4% vs 11.8% +/- 4.5% of the left ventricle, difference not significant). Since the rate of disappearance of LCII is rapid and was not affected by MP, these results suggest that MP treatment early after acute MI delays breakdown of myosin filaments, but cannot prevent it.

Mapping of ventricular tachycardia induced by programmed stimulation in canine preparations of myocardial infarction

To investigate the mechanism of uniform ventricular tachycardia induced by programmed stimulation, we recorded His bundle electrograms and unipolar electrograms from 64 subepicardial, subendocardial, and intramural sites in dogs. Isochronal maps were generated off-line by computer. Two groups of dogs were studied 3 days after occlusion of their left anterior descending coronary arteries; one group underwent reperfusion after 2 to 2.5 hr of occlusion and the other methylprednisolone treatment before permanent occlusion. In the former, subepicardial sequences presented either a pattern suggesting circus movement or a radial pattern in which excitation at intramural sites could precede earliest subepicardial excitation. In the latter preparations, subepicardial excitation patterns consistently suggested circus movement in the subepicardial muscle layer surviving over necrotic tissue. Assuming complete circus movement, the "missed" time interval, measured as the interval left unaccounted for by actual recording of local excitation between ventricular tachycardia cycles, ranged from 3% to 64% of the cycle length of ventricular tachycardia. While surviving subepicardial and intramural layers appeared to be involved in the mechanism of ventricular tachycardia, a late second breakthrough on the right ventricle, in conjunction with fixed-coupled H deflections on the His bundle electrograms, suggested the involvement of the conducting system in propagation of the impulse.

Electrocardiographic changes after streptokinase-induced recanalization in patients with acute left anterior descending artery obstruction

ECG changes were assessed in 15 patients in whom intracoronary streptokinase recanalized a totally occluded left anterior descending artery during acute myocardial infarction. These results were compared retrospectively with those in 22 comparable conventionally treated patients who underwent catheterization during the acute stage of infarction. Before angiography no significant differences were found in the sum of ST elevation (sigma ST increase V1-V6), the sum of R waves (sigma RV1-V6), or the number of Q waves (nQV1-V6) in leads V1 through V6. sigma ST increase V1-V6 was significantly lower in the streptokinase group than in control patients at all times after angiography. sigma RV1-V6 declined and nQV1-V6 increased in both groups during the first 12 hr, but there was no further change in the control group, whereas in the streptokinase group a significant increase in sigma RV1-V6 and decrease in nQV1-V6 followed. There was a significant correlation between long-term electrocardiographic (sigma RV1-V6; nQV1-V6) and angiographic findings (ejection fraction, akinetic segment length). Thus, the Q wave regression and increase in sigma RV1-V6 after streptokinase suggest, in accordance with angiographic findings, that jeopardized myocardium was salvaged by reperfusion.

Failure of methylprednisolone to prevent nonuniform cardiac accelerator nerve discharge associated with coronary occlusion-induced arrhythmia: evidence against prostaglandin modulation of autonomic cardioaccelerator neural discharge in the anesthetized cat

Postganglionic cardiac sympathetic neural discharge in the minute prior to arrhythmia produced by acute occlusion of the left anterior descending coronary artery was nonuniform, i.e., both increases or decreases occurred. It is hypothesized that the nonuniform neural discharge is transmitted to the heart, causing nonuniform changes in excitability and conduction which produce ventricular arrhythmias. Prostaglandins have been shown to exhibit both arrhythmogenic as well as antiarrhythmic actions. Methylprednisolone (30 or 50 mg/kg, i.v., a known inhibitor of prostaglandin synthesis) was given 30 minutes prior to coronary occlusion of the left anterior descending artery. Both doses of methylprednisolone failed to: exert any effect on the mean postganglionic cardiac sympathetic nerve discharge prior to coronary occlusion; eliminate the nonuniform neural discharge associated with occlusion-induced arrhythmia; increase the time to arrhythmia or death; and decrease the number of cats dying after acute coronary occlusion. Thus, it is hypothesized that methylprednisolone failed to prevent the arrhythmogenic actions of prostaglandins. The failure of methylprednisolone to decrease the time to arrhythmia suggests that, in this study, an antiarrhythmic mechanism for prostaglandins does not exist. The failure of methylprednisolone to prevent the occlusion-induced nonuniform cardiac sympathetic discharge suggests that prostaglandin modulation of the autonomic balance on the heart is not due to a direct action on the postganglionic cardiac sympathetic nerve.

Quantitative effect of early coronary artery reperfusion in baboons. Extent of salvage of the perfusion bed of an occluded artery

We examined the extent to which ischemic myocardium was salvaged by reperfusion using a method that allowed expression of the volume of infarction as a percentage of the volume of the perfusion bed of the occluded artery (region at risk of infarction). In eight baboons, the left anterior descending coronary artery (LAD) was occluded for 2 hours, after which perfusion was restored. A control group of eight baboons underwent an identical protocol, but perfusion was not restored. Twenty-four hours after occlusion, microvascular dyes were injected into the LAD and adjacent arteries to delineate the perfusion bed of the occluded artery. The volume of infarction and volume of the perfusion bed were determined planimetrically. The mean percentage of the perfusion bed infarcted in the control baboons was 94.2 +/- 3.5% and 50.1 +/- 5.8% in the reperfused baboons. Hence, the mean percentage of the perfusion bed infarcted was reduced by 44.1% in the reperfused group compared with the control group (p less than 0.001). In reperfused baboons, hemorrhage occurred in the region of infarction but did not result in infarct extension. We conclude that reperfusion after 2 hours of coronary occlusion results in substantial salvage of ischemic myocardium in the baboon.

Effects of methylprednisolone on the ischemic damage in patients with acute myocardial infarction

In this double-blind randomized study, 19 patients with acute transmural myocardial infarction were treated with methylprednisolone administered 4.4 +/- 0.7 hours (+/- SEM) after the onset of chest pain, and were compared with 21 patients who received placebo 4.5 +/- 0.4 hours after the start of clinical symptoms. The two groups were comparable in reference to sex, prevalence of risk factors, clinical status on admission, location of myocardial infarction and magnitude of ischemic injury as assessed by standard ECGs and precordial ST-segment and QRS maps. The treated patients, however, were older than the patients who received placebo. Methylprednisolone in an i.v. dose of 2.0 g was administered on admission and a similar dose was infused 3 hours later. Placebo administration followed an identical schedule. Mortality, cardiac rupture, incidence of ventricular arrhythmias, blocks, extension of myocardial infarction, pericarditis, postinfarction chest pain, persistent ST-segment elevation at discharge, and change in Killip class during hospitalization were the same in both groups. Peak enzyme values, and changes in ECG variables pertaining to resolution of ST-segment elevation or development of QRS evolutionary alterations were similar in both groups. Follow-up for 6 months did not reveal any differences in the clinical course of the two groups. Methylprednisolone infused in a total dose of 4.0 g within 12 hours after the onset of chest pain in patients with acute transmural myocardial infarction does not result in any demonstrable beneficial or harmful effects.

Prevention of calcium paradox-related myocardial cell injury with diltiazem, a calcium channel blocking agent

The effect of diltiazem on creatine kinase release and tissue adenosine triphosphate content was investigated during calcium paradox in the isolated perfused rat heart. Creatine kinase loss was minimal during the calcium-free phase, but there was a 100-fold increase in creatine kinase release after reperfusion with normal calcium-containing medium. Diltiazem reduced creatine kinase loss by 35 percent when added to calcium-free medium and by approximately 80 percent when added to both calcium-free and reperfusion media. Adenosine triphosphate content was significantly increased from 2.98 mumol in untreated calcium paradox hearts to 5 mumol/g dry weight in diltiazem-treated hearts. With hypothermia the calcium paradox injury was completely inhibited if the temperature of calcium-free perfusion was maintained at 15 degrees C. Diltiazem appears to exert its protective effect through its ability to prevent the cellular separation and alterations in the gap junctions during calcium deprivation of cells and to limit calcium entry into the cells after reperfusion with calcium-containing medium.

Ineffectiveness of methylprednisolone to reduce infarct size in experimental coronary occlusion

Two medium-sized branches of the left coronary artery were prepared in each of 10 anesthetized open chest dogs for later occlusion. The first artery was occluded during 90 minutes and reperfused thereafter. This occlusion produced the control infarct. Methylprednisolone (50 mg/kg i.v.) was injected and the second artery was occluded also for 90 minutes and reperfused thereafter. Both infarcts were made visible by staining left ventricular rings with p-nitrobluetetrazolium. Infarct size was compared with the size of the perfusion area, which we obtained from the postmortem angiogram. Both infarcts were equal in size and comprised 50% of the area of perfusion of the occluded artery. Methylprednisolone in a single high dose given prophylactically did not influence infarct size nor any of the measured parameters.

Failure of nifedipine therapy to reduce myocardial infarct size in the baboon

The value of nifedipine in reducing the ultimate size of an infarct associated with a period of coronary occlusion followed by reperfusion was assessed. Eight baboons were administered a bolus dose of nifedipine, 5 micrograms/kg intravenously, and then a maintenance dose of 30 micrograms/kg per hour was begun 1 hour before occlusion. This regimen resulted in an 8.5 +/- 1.2 percent (mean +/- standard error) decrease in mean arterial pressure. The left anterior descending coronary artery was occluded for 2 hours and then perfusion restored. At 2 hours after reperfusion the nifedipine infusion was discontinued. Eight control baboons underwent an identical protocol without nifedipine therapy. At 24 hours after occlusion, microvascular dyes were injected into the left anterior descending coronary artery and adjacent arteries to delineate the perfusion bed of the previously occluded artery. The volume of infarction was determined with planimetry and compared with the volume of the perfusion bed of the occluded artery. The area of infarction was always contained within the perfusion bed of the occluded artery. The mean percent of the perfusion bed with infarction was 50.1 +/- 5.8 in the control group and 41.7 +/- 9.5 in the treated group (difference not significant; p greater than 0.05). In both control and treated groups of baboons hemorrhage occurred only within the region of infarction. In both groups electron microscopy revealed large electron-dense granules within the mitochondria. In conclusion nifedipine therapy during a 2 hour period of coronary occlusion followed by reperfusion did not result in any significant reduction in ultimate infarct size in the baboon.

Prostaglandins in myocardial: with emphasis on myocardial preservation

Various therapies during early hours of acute myocardial infarction (AMI) have been suggested to protect ischemic myocardium and reduce infarct size. Despite reports that prostaglandins (PGs) are released during myocardial ischemia, and that prostacyclin (PGI2) and thromboxane A2 (TXA2) have opposing effects on vasomotion and platelet aggregation, the physiologic roles of PGs, PGI2 and TXA2 in AMI have not been clearly defined. However, in pharmacologic doses, experimental evidence suggests that vasodilator PGs might be beneficial, and vasoconstrictor PGs might be deleterious, in AMI. Recent recognition that coronary spasm is frequent in AMI has led to the notion that an increased PGI2/TXA2 ratio might be desirable. Thus, exogenous PGE1, exogenous PGI2 or tis more stable analogs, drugs that stimulate PGI2 release, and inhibitors of TXA2 and harmful PGs are potential agents for protective therapy in AMI.

An isolated, blood-perfused, feline heart preparation for evaluating pharmacological interventions during myocardial ischemia

A preparation is described in which feline hearts were perfused with arterial blood drawn from a blood-donor cat. Ventricular function was measured with a fluid-filled latex balloon within the left ventricle. Left ventricular developed pressure, maximum left ventricular dP/dt, ventricular compliance, and coronary blood flow changed only slightly during two hours of perfusion at a constant pressure of 75 mmHg. Water, sodium, potassium, and calcium contents, and creatine kinase activity of isolated hearts did not differ from the values obtained for intact hearts from the blood-donor cats. Isolated hearts subjected to 40 minutes of normothermic global ischemia with one hour of reperfusion exhibited significantly decreased contractility, but no change in ventricular compliance. Myocardial water and sodium contents were increased after 40 minutes of ischemia and reperfusion. Hearts subjected to 60 minutes of ischemia with reperfusion exhibited decreases in both contractility and compliance. A prolonged reactive hyperemic response was maintained throughout the hour of reperfusion. Myocardial sodium content increased more than could be accounted for by edema formation; decreases were observed in potassium content and creatine kinase activity while calcium content was increased. The applicability of this model for evaluating the effects of pharmacological interventions on myocardial ischemic injury are discussed.

Corticosteroids in acute myocardial infarction

Forty-two patients admitted to the Coronary Care Unit with a diagnosis of acute myocardial infarction were studied within 24 hours of the onset of symptoms. In addition to therapy determined by the attending physician, there was a double-blinded administration of either a placebo or methylprednisolone, 30 mg/kg intravenously every 6 hours for four doses. This drug had no beneficial effect on infarct size, dysrhythmias, complications, or left ventricular function 2 weeks after infarction.

Mechanism of the beneficial effect of dexamethasone on myocardial cell integrity in acure myocardial ischemia

Dexamethasone (6 mg/kg) given intravenously to anesthetized cats exerted no significant hemodynamic effect on control open-chest cats or in cats subjected to acute myocardial ischemia by coronary artery ligature. However, dexamethasone normalized elevated S-T segments toward preischemic values, and prevented much of the increase in plasma CPK activity following coronary artery ligation. Moreover, dexamethasone prevented loss of CK activity within ischemic myocardial tissue five hours after the onset of ischemia. Dexamethasone also reduced the extent of ischemic damage as assessed by a nitro-blue tetrazolium staining technique, providing anatomic verification of the reduced ischemic damage. Moreover, dexamethasone prvented the swelling and vacuolization of myocardial lysosomes in the ischemic region, indicating a stabilization of lysosomal membranes within the heart. These data indicate that lysosomal disruption is an important consequence of myocardial ischemia and that early treatment with dexamethasone prevents the loss of myocardial lysosomal and cellular enzymes as reflected in normalization of the ECG and plasma CK activity of ischemic cats. In this way, dexamethasone may act to retard the spread of the developing infarct within the ischemic myocardium.

Reduction of cell injury in hypoxic cultures of rat myocardial cells by methylprednisolone

An in vitro model to study myocardial cell injury was developed with primary monolayer cultures of rat myocardial cells. Two important conditions associated with myocardial ischemia were simulated by depriving the cultures of oxygen and glucose for a specified period of time. Cellular injury caused by hypoxia and glucose deprivation resulted in significant leakage of lactate dehydrogenase (LDH) from the cells into the culture medium. The cells were not lethally injured by treatments as reflected by a lack of change in cell viability and protein content when compared to controls. Pretreatment of cultures with methylprednisolone for 24 hr provided protection to the cells when challenged by hypoxia and glucose deprivation. Methylprednisolone exhibited a dose-response effect in reducing LDH leakage in cultures, which were subsequently deprived of oxygen and glucose for 4 hr. Similar pretreatment with hydrocortisone had no effect in limiting cellular injury in hypoxic and glucose-deprived cultures.

Lack of effect of methylprednisolone on lysosomal and microsomal enzymes after two hours of well-defined canine myocardial ischemia

Myocardial ischemia was produced for 2 hours by coronary ligation in 11 dogs pretreated with methylprednisolone (MP, 30 mg/kg). Myocardial blood flow (MBF) was measured with microspheres (15 micrometer) in each tissue sample used for enzymatic analysis. Homogenates of these tissue samples were separated by ultracentrifugation into lysosome-rich and microsomal fractions and were analyzed for N-acetyl-beta-glusosaminidase (NAGA), beta-glucuronidase (beta-gluc), rotenone-insensitive-NADH-cytochrome c reductase (RINCR), and cytochrome oxidase. The enzymatic data from centrifugal fractions were grouped according to MBF values for statistical analysis of inter-group effects of ischemia. Significant losses (P less than 0.001) of NAGA and beta-gluc were seen in all MP-treated lysosome-rich particulate fractions that were isolated from zones demonstrating MBF values less than 25% of control (L-ischemia). Similar significant losses (P less than 0.001) of RINCR were seen in microsomal fractions from L-ischemia zones. Samples with MBF values greater than 25% but less than 75% of control (M-ischemia) also demonstrated significant decreases of lysosomal and microsomal enzymatic activity in specific fractions. When the data of the above MP-treated group were compared with the untreated control group, no significant intergroup effects of treatment with MP were observed. In addition, enzymatic data (NAGA, RINCR) were normalized prior to performing linear regression analyses; percent loss of particulate enzymatic activity was plotted against percent decrease in MBF. The effects of 2 hours of ischemia on the above biochemical parameters were comparable between untreated and MP-treated groups. Finally, when myocardial samples were grouped according to similar levels of MBF, statistical analysis using the general linear models procedure revealed no beneficial effect of MP treatment on changes in lysosomal hydrolases, microsomal RINCR, or latency of lysosomes.

Influence of methylprednisolone of the sequential redistribution of cathepsin D and other lysosomal enzymes during myocardial ischemia in rabbits

Occlusion of the circumflex coronary artery induced a profound redistribution in ischemic rabbit myocardium of several lysosomal acid hydrolases, including cathepsin D, B-acetylglycosaminidase, and acid phosphatase. 30-45 min after ligation non-sedimentable cathepsin D activity rose from 36% of the total activity to 42-48%, and in immunohistochemical preparations cathepsin D appeared to have diffused from lysosomes into the cytosol of injured cells. A pharmacologic dose of methylprednisolone (50mg/kg) significantly delayed the subcellular redistribution of cathepsin D and the other hydrolases in ischemic heart. Thus, in treated hearts the nonsedimentable activity of cathepsin D rose to only 38% after 30 min of ischemia and 42% after 45 min (P is less than 0.05 compared to untreated ischemia at each time). Similarly, unlike untreated hearts, noevidence of enzyme diffusion from lysosomes could be demonstrated immunohistochemically in corticosteroid-treated ischemic hearts for over 45 min. After 1-2 h of ischemia, however, steroid-protected myocytes deteriorated and the biochemical activity and anatomical distribution of cathepsin D were indistinguishable from untreated ischemic hearts. This study demonstrates that corticosteroid pretreatment does not prevent alterations in cardiac lysosomes during severe ischemia indefinitely, but does delay their development significantly.

Computed tomography for localization and sizing of experimental acute myocardial infarcts

Computed tomography (CT) has been used to quantitate acute myocardial infarct size in isolated, arrested canine hearts. Acute myocardial infarcts were produced in 20 hearts by either left anterior descending (13 dogs) or circumflex coronary artery ligation (seven dogs). Each animal was given iodinated contrast media intravenously immediately before sacrifice 24--72 hours postinfarction. All infarcts greater than 1 g and one of three infarcts 0.5 g or less were detected by CT imaging. Infarct volume determined by CT correlated with gross infarct weight (r=0.83). CT imaging, however, consistently underestimated infarct volume; underestimation was largest in a group of patchy, predominantly subendocardial infarcts. As adequate equipment and techniques for in vivo studies are developed, CT imaging of the heart may become important in clinical evaluation of myocardial infarction.

Topical cardiac hypothermia: the effect of methylprednisolone sodium succinate

We evaluated the effects of methylprednisolone sodium succinate (MPSS) on 60 minutes of myocardial ischemia during profound (5 degrees C) topical cardiac hypothermia (ice chips) in a canine right heart bypass preparation. The ventricular function curve shifted to the right and downward, but not significantly, after ischemia, and stroke work declined significantly for both control and treated dogs. Contractility (rate of rise of left ventricular pressure and maximum velocity of the contractile element) declined for both groups but not significantly. Total coronary flow, oxygen consumption, and metabolism of lactate and pyruvate were not different for control and treated dogs. Ultrastructure of the outer and inner myocardium did not demonstrate benefit from MPSS. Intracellular and extracellular edema of moderate severity was slightly worse in the subendocardium, and reversible mitochondrial injury of a mild to moderate degreee was symmetrically present. Ice-related injury was not noted. We were unable to deomonstrate that pretreatment with MPSS favorably alters cardiodynamics or ultrastructure after 60 minutes of profound topical cardiac hypothermia.

Failure of methylprednisolone to protect acutely ischemic myocardium: a contrast with subsequent beta-adrenergic blockade in man

Two grams of methylprednisolone was administratered to ten patients with acute myocardial infarction at an average of 13 hours from the onset of symptoms; pain in the chest was not relieved in six of the ten patients. In one hour, no significant improvement was noted in the function of the ischemic segments (examined using a multiaxis echocardiographic method) or in the S-T segments of the 12-lead electrocardiogram. Left ventricular filling pressure soon increased by an average of 4 mm Hg (P less than 0.005), without ventricular dilatation or a Frank-Starling response, suggesting a decrease (ischemic?) in myocardial compliance. Cardiac output by Swan-Ganz thermodilution later increased by 21 percent (P less than 0.01) when a decrease in peripheral vasoconstriction was evident. In contrast, small-dose beta-adrenergic blockade using 0.2 mg of pindolol intravenously after administration of methylprednisolone immediately relieved pain in the chest in all six patients. Elevation of the S-T segments was reduced by 34 percent (P less than 0.05) within 15 minutes, and the contractile function of the ischemic segments improved markedly, by 3 mm or to 34 percent of normal, from the 4 percent of normal before administration of pindolol (P less than 0.005). Hemodynamic function did not deteriorate in the eight patients with uncomplicated infarction or moderate left ventricular failure. Therapy with pindolol thus reduced clinical, electrocardiographic, and myocardial mechanical signs of acute ischemia safely, while administration of methylprednisolone had no short-term protective effect.

Effect of therapy with methylprednisolone on the size of myocardial infarcts in man

The use of steroids to decrease the size of the infarct and the mortality in patients with acute myocardial infarction has long been the subject of controversy. In the present study, two large doses of methylprednisolone were administered intravenously to 14 patients with relatively uncomplicated myocardial infarction within 17 hours after the onset of symptoms, whereas a comparable group of 15 patients with myocardial infarction served as controls. The size of the infarct was assessed utilizing serial measurements of serum levels of creatine phosphokinase and its myocardial isoenzyme, the MB form of creatine phosphokinase. There was no significant difference between the two groups of patients with regard to peak cumulative levels of total creatine phosphokinase and the MB form of creatine phosphokinase. Similarly, there was no difference between the two groups in mortality or in the incidence of malignant ventricular arrhythmias, atrioventricular block, congestive heart failure, or extensions of the infarct. We conclude that high intravenous doses of steroids given early in the course of myocardial infarction have neither deleterious nor beneficial effects.

Long-term preservation of ischemic myocardium after experimental coronary artery occlusion

The results of experiments with indirect methods have suggested that various interventions reduce infarct size after coronary artery occlusion. To determine and quantify directly both the short- and long-term effects of several interventions on myocardial salvage without relying on indirect methods, the left coronary artery was occluded in 880 rats; they were then given either no treatment or one of the following interventions: (a) hyaluronidase, an enzyme that hydrolyzes interstitial glycoproteins, 1,500 National Formulary (NF) U/kg i.v. 5 min and 24 h after occlusion; (b) cobra venom factor, a protein that depletes the third component of complement, 20 U/kg i.v. 5 min after occlusion; (c) a glucocorticoid: hydrocortisone, 50 mg/kg i.v. 5 min after occlusion; or the five-fold more potent methylprednisolone (MP): (i) 50 mg/kg i.v. 5 min after occlusion or (ii) 50 mg/kg i.v. 5 min after occlusion followed by 50 mg/kg i.m. 3, 6, and 24 h after occlusion; or (d) reserpine, an agent that depletes the heart of catecholamines, 0.5 mg/kg i.m. once on each of the 3 days before occlusion. The animals were sacrificed either 2 days after occlusion, i.e., at the time of peak necrosis, or after 3 wk, i.e., after the infarct was completely healed. The amount of preserved myocardium was then assessed by two independent techniques: planimetric measurement of serial histologic sections and creatine kinase activity of the whole left ventricle. The amount of normal myocardium preserved at 21 days postocclusion was significantly increased, by 22.3+/-7.8% (P < 0.025) after the administration of hyaluronidase, by 25.3+/-5.8% (P < 0.005) after cobra venom factor, by 14.5+/-6.9% (P < 0.05) after hydrocortisone, by 20.8+/-8.2% (P < 0.025) after the single dose of MP, by 20.9+/-3.9% (P < 0.001) after the four doses of MP, and by 10.2+/-3.7% (P < 0.05) as a result of pretreatment with reserpine. The four doses of MP significantly thinned the infarct-by 25.6+/-2.9% (P < 0.001)-and although ventricular rupture did not occur, the intervention caused distension of the left ventricle as a result of stretching of the infarcted tissue during scar formation. Thus, myocardium acutely jeopardized by ischemia can be preserved on a long-term basis.

Mummification of the infarcted myocardium by high dose corticosteroids

There is evidence that glucocorticoids reduce infarct size but their use in myocardial infarction remains controversial because of their potential adverse effects on healing of the infarct. To investigate the healing process, rats received either four parenteral doses of 50 mg/kg of methylprednisolone (MP) or saline 5 min, 3,6 and 24 hr after coronary occlusion and their hearts were examined by light and electron microscopy 48 hr and seven days after occlusion. At 48 hr, in five untreated rats, only 12 +/- 7% of injured myocytes showed the persistence of striations and a relatively intact sarcolemma despite loss of nuclei and hence appeared "mummified" whereas in six MP-treated rats 72 +/- 8% of myocytes exhibited this appearance (P less than 0.001). In treated rats there were fewer phagocytes than in controls. At seven days, in seven MP-rats, mummified cells were still more prominent than in five untreated rats and there were fewer phagocytes and less collagen. In conclusion, high dose of MP delays the inflammatory process and retards the disintegration of necrotic myocytes, resulting in impaired healing.

Effect of methylprednisolone upon technetium-99m pyrophosphate assessment myocardial necrosis in the canine countershock model

Repeat DC countershock reproducibly results in myocardial necrosis in dogs. In this model, myocardial technetium-99m pyrophosphate (PYP) uptake correlates linearly with tissue creatine kinase depletion (r = -0.83). The effect of pretreatment with methylprednisolone (MP) was studied with PYP in 25 dogs. In myocardium damaged by countershock, 12 MP dogs had higher tissue radioactivity sample:normal (S:N) ratios than control (P less than 0.05), suggesting increased tissue injury. However, by several other measures of tissue damage, the two groups did not differ. MP-elevated PYP S:N ratios were explained by reduced PYP activity in normal myocardium of MP dogs. Further experiments in 21 dogs revealed that renal PYP clearance, which correlated with glomerular filtration rate (GFR) as measured by creatinine clearance, was increased in Mp dogs, resulting in accelerated urinary excretion of PYP (46.9+/-3.6 vs 35.8+/-2.4 percent injected dose in one hour, P less than 0.01), and reduced blood PYP. Thus MP does not modify countershock-induced myocardial injury. However, by increasing GFR, MP increased PYP excretion, resulting in lowered blood and normal zone myocardial PYP, thereby spuriously affecting myocardial PYP tissue uptake data.