Depressed myocardial creatine phosphokinase activity following experimental myocardial infarction in rabbit

Biomechanics of infarcted left Ventricle-A review of experiments

Myocardial infarction (MI) is one of leading diseases to contribute to annual death rate of 5% in the world. In the past decades, significant work has been devoted to this subject. Biomechanics of infarcted left ventricle (LV) is associated with MI diagnosis, understanding of remodelling, MI micro-structure and biomechanical property characterizations as well as MI therapy design and optimization, but the subject has not been reviewed presently. In the article, biomechanics of infarcted LV was reviewed in terms of experiments achieved in the subject so far. The concerned content includes experimental remodelling, kinematics and kinetics of infarcted LVs. A few important issues were discussed and several essential topics that need to be investigated further were summarized. Microstructure of MI tissue should be observed even carefully and compared between different methods for producing MI scar in the same animal model, and eventually correlated to passive biomechanical property by establishing innovative constitutive laws. More uniaxial or biaxial tensile tests are desirable on MI, border and remote tissues, and viscoelastic property identification should be performed in various time scales. Active contraction experiments on LV wall with MI should be conducted to clarify impaired LV pumping function and supply necessary data to the function modelling. Pressure-volume curves of LV with MI during diastole and systole for the human are also desirable to propose and validate constitutive laws for LV walls with MI.

The efficacy and tolerability of azilsartan in obese insulin-resistant mice with left ventricular pressure overload

Angiotensin II receptor blockers (ARBs) are used widely for the treatment of heart failure. However, their use in obese and insulin-resistant patients remains controversial. To clarify their potential efficacy in these conditions, we administered azilsartan medoxomil (azilsartan), a prodrug of an angiotensin II receptor blocker to mice fed a high-fat diet (HFD) with left ventricular (LV) pressure overload (aortic banding). LV fibrosis (hydroxyproline), cardiac plasminogen activator inhibitor-1 (PAI-1; a marker of profibrosis), and creatine kinase (a marker of myocardial viability and energetics) were assessed. LV wall thickness and cardiac function were assessed echocardiographically. Mice given a HFD were obese and insulin resistant. Their LV hypertrophy was accompanied by greater LV PAI-1 and reduced LV creatine kinase compared with normal diet controls. Drug treatment reduced LV wall thickness, hypertrophy, and PAI-1 and increased cardiac output after aortic banding compared with results in HFD vehicle controls. Thus, azilsartan exerted favorable biological effects on the hearts of obese insulin-resistant mice subjected to LV pressure overload consistent with its potential utility in patients with analogous conditions.

Erythropoietin to augment myocardial salvage induced by coronary thrombolysis in patients with ST segment elevation acute myocardial infarction

To determine whether the administration of erythropoietin (EPO) early after the onset of ischemia could enhance the preservation of jeopardized myocardium by reperfusion, 236 patients admitted <6 hours after the onset of chest pain indicative of acute coronary syndromes confirmed to be ST-segment elevation acute myocardial infarctions who were treated with tenecteplase to induce coronary thrombolysis were studied. Patients were randomized to standard care or standard care plus the administration of a single dose of EPO 30,000 IU intravenously immediately before the onset of treatment with tenecteplase. The primary end point was enzymatically estimated infarct size. The results indicated that infarct size index was virtually identical in the 2 groups, with a mean +/- SE of 13.2 +/- 0.1 creatine kinase-MB gram equivalents in controls and 12.4 +/- 0.9 creatine kinase-MB gram equivalents in patients treated with EPO. In conclusion, although the early administration of EPO was apparently safe, it did not enhance the preservation of jeopardized ischemic myocardium.

Factors of importance for the degree of ischemic injury in the isolated rat heart

Isolated working rat hearts were made ischemic by introducing a one-way aortic ball valve. After the ischemic period the hearts were perfused in a retrograde non-working way for 30 min. Flow rates, glycogen, ATP, and creatine-phosphate went down during the time of ischemia, whereas tissue lactate accumulated. For shorter periods of ischemia these values were normalized but after 30 min of ischemia the hearts seemed to be irreversibly damaged. There was a leakage of GOT, GPT, LDH, and CPK from all hearts when ischemic from 5 to 30 min. Different factors that might be of importance for the degree of ischemic injury were tested. The injury tended to be more severe at higher heart rates. Addition of adrenaline 10(-6)M resulted in excessive myocardial damage. A variation of pH from 7.1 to 7.7 did not alter the effects of the ischemic injury. One group of rats were injected with adrenaline for 8 weeks to simulate chronic stress. When hearts from these rats were made ischemic they were more prone to fail compared to controls. The failing hearts, on the other hand, had a lower leakage of enzymes, possibly due to a less severe myocardial damage. A high mechanical performance and a normal noradrenaline content of the hearts are key factors for the development of myocardial infarction, as indicated by this study.

A Profibrotic Effect of Plasminogen Activator Inhibitor Type-1 (PAI-1) in the Heart

Increased expression of PAI-1 is profibrotic in several organs. However, its potentially profibrotic effects in the heart subjected to infarction have not been elucidated. Accordingly, we induced coronary occlusion in 10-week-old mice congenic on a C57BL6 background and in mice overexpressing PAI-1 (PTG) in multiple tissues. Compared with C57BL6 control mice without myocardial infarction (MI), PTG mice exhibited consistently elevated PAI-1 in plasma at 16 weeks of age but virtually identical PAI-1 content in left ventricular (LV) myocardium. However, they exhibited a 2-fold increase in LV PAI-1 content 6 weeks after induction of MI (4.21 ± 1.0 ng/ml tissue protein) compared with that in C57BL6 mice (2.04 ± 0.5, P < 0.05). In 16-week-old mice, ultrasonically delineated LV fractional shortening (FS) was comparable in normal PTG and normal C57BL6 controls. However, 6 weeks after MI, PTG ( n = 21) compared with C57BL6 ( n = 14) mice exhibited markedly thinner LV posterior walls in both diastole (C57BL6 0.79 ± 0.05 mm, PTG 0.55 ± 0.06, P < 0.05) and systole (0.97 ± 0.05 mm, 0.75 ± 0.06, P < 0.05); increased end systolic LV dimensions (4.54 ± 0.2 mm, 5.17 ± 0.2, P < 0.05); and significantly depressed FS, more impaired LV segmental function, and greater mitral E wave amplitude. Compared with fibrosis assessed by Masson staining of sections from apex to base in C57BL6 mice (10.85 ± 0.43% LV area), PTG mice exhibited 33% more LV fibrosis after MI ( P < 0.05). Thus, PAI-1 is profibrotic in the heart subjected to infarction. Accordingly, overexpression of PAI-1 is a promising target for attenuation of heart failure after MI that may be exacerbated by fibrosis.

Attenuation of apoptosis and the eye of the beholder

OBJECTIVES

We consider the conundrum suggested by myocardial hibernation and late restoration of function despite the absence of a substantial lateral peri-infarction border zone with respect to oxygenation, and suggest a pivotal role for apoptosis and its attenuation in salvaging jeopardized myocardium.

METHODS

Selective pertinent literature is reviewed, and some recent observations indicating difficulties in identifying and quantifying apoptosis microscopically are summarized.

RESULTS

Apoptosis seems to occur primarily after reperfusion following ischemia rather than persistent ischemia leading to necrosis. Refinements of markers of its presence are needed in vitro for use ultimately in vivo and should be pivotal in defining the extent to which tissue-protective interventions can salvage myocardium in the context of a fixed magnitude and duration of ischemia.

CONCLUSION

Apoptosis is strongly implicated in the overall demise of jeopardized myocardium. Its attenuation seems likely to be potentially beneficial. Validation of this hypothesis will require progress in identification, delineation, and assessment of the extent of apoptosis in the threatened heart.

Deleterious effects of lack of cardiac PAI-1 after coronary occlusion in mice and their pathophysiologic determinants

We sought to delineate mechanisms through which the lack of plasminogen activator inhibitor (PAI)-1 in the heart affects remodeling of the heart early after myocardial infarction (MI). MI was induced by coronary occlusion in 10-weeks old PAI-1 knockout (KO) and control mice. Three days after MI, systolic and diastolic function was assessed with high-resolution echocardiography, infarct size was determined biochemically and histologically and accumulation of acute inflammatory cells in zones of infarction was characterized by immunocytochemistry. PAI-1 KO mice exhibited markedly thickened diastolic left ventricular anterior walls (1.38 +/- 0.38 mm vs. 0.77 +/- 0.13 SD), more profound depression of global and regional cardiac function (19 vs. 22% fractional shortening), and greater evidence of diastolic dysfunction (average E wave amplitude = 568 vs. 675 mm/s) all of which were significant. Markedly greater extent of infarction was demonstrated biochemically and histologically in knockout mice compared with controls (76 vs. 29% of the left ventricle, P < 0.05) associated with striking hemorrhage and intense inflammation. Fibrosis normalized for infarct size was markedly reduced (0.006 vs. 0.022 microg hydroxyproline/mg dry weight). Thus, lack of PAI-1 in the heart exerted deleterious effects mediated, at least in part by increased inflammation and hemorrhage and attenuating of fibrosis.

Gender specific effect of progesterone on myocardial ischemia/reperfusion injury in rats

The study was designed to investigate the effect of progesterone and its gender based variation on myocardial ischemia/reperfusion (I/R) injury in rats. Adult Sprague Dawley rats were divided into vehicle treated reperfusion injury group male (I/R-M), female (I/R-F), ovariectomised (I/R-OVR) and progesterone treatment (I/R-M+PG, I/R-F+PG, I/R-OVR+PG) groups, respectively. I/R injury was produced by occluding the left descending coronary artery (LCA) for 1 h and followed by re-opening for 1 h. Progesterone (2 mg kg(-1) i.p.) was administered 30 min after induction of ischemia. Hemodynamic parameters (+/-dp/dt, MAP), heart rate, ST-segment elevation and occurrence of ventricular tachycardia (VT) were measured during the I/R period. The myocardial infarct area, oxidative stress markers, activities of myeloperoxidase (MPO) and creatine kinase (CK) were determined after the experiment along with the assessment of the effect on apoptotic activity by using DNA fragmentation analysis. Histological observations were carried out on heart tissue. Treatment with progesterone significantly (P<0.05) reduced infarct area, lipid peroxidation (LPO) level and activity of MPO in females (I/R-F+PG) as compared to ischemic females (I/R-F). Progesterone significantly (P<0.001, P<0.05) inhibited serum CK activity and incidences of VT in female rats. Superoxide dismutase (SOD) activity, reduced glutathione (GSH) levels were significantly elevated (P<0.05) in I/R-F+PG group. Internucleosomal DNA fragmentation was less in I/R-F+PG group when compared to I/R-F group. The ischemic male and ovariectomised (I/R-M and I/R-OVR) counterparts did not show any significant change after progesterone treatment. In conclusion, the cardioprotective effect of progesterone on myocardial I/R injury induced damage is based on gender of the animal. The protective effect could be mediated by attenuation of inflammation and its possible interaction with endogenous estrogen.

Insulin resistance increases PAI-1 in the heart

To determine whether insulin resistance increases expression of plasminogen activator inhibitor type-1 (PAI-1) in the heart, studies were performed in 22 mice with and 38 without myocardial infarction. Insulin resistance in transgenic animals genetically rendered insulin resistant was confirmed with the use of intraperitoneal glucose tolerance tests. Myocardial infarction was induced by coronary ligation, verified echocardiographically, and quantified by assay of depletion of creatine kinase (CK) from the left ventricle 2 weeks later. PAI-1 increased markedly in zones of infarction to 10.4+/-2.1 (SF) and significantly more to 27.3+/-3.6 in normal and insulin resistant mice compared with 0.45+/-0.04 and 0.50+/-0.03 in normal myocardium. Thus, insulin resistance induced accumulation of PAI-1 in the heart, particularly in zones of infarction. Such increases may contribute to fibrosis and diastolic dysfunction typical late after infarction in patients with insulin resistance.

Cardioprotective effects of the serine protease inhibitor aprotinin after regional ischemia and reperfusion on the beating heart

OBJECTIVE

Early coronary reperfusion of the ischemic myocardium is a desired therapeutic goal to preserve myocardium. However, reperfusion itself contributes to an additional myocardial injury (ie, reperfusion injury), which has been attributed to neutrophil infiltration with subsequent release of proteases and oxygen-derived radicals. We studied the effects of the serine protease inhibitor aprotinin (Trasylol) on myocardial ischemia and reperfusion in a rat model.

METHODS

The effects of aprotinin (5000 and 20,000 U/kg) were examined in vivo in a rat model of regional myocardial ischemia (20 minutes) and long-term reperfusion (24 hours). Cardioprotecive effects were determined by means of measurement of creatine kinase and myeloperoxidase activity within the myocardium, as well as histochemical analysis.

RESULTS

Aprotinin (20,000 U/kg) administrated 2 minutes before reperfusion significantly attenuated myocardial injury expressed as creatine kinase washout compared with that seen in vehicle-treated rats (65 +/- 25 vs 585 +/- 98 creatine kinase difference in units per 100 mg, P <.01). Administration of 5000 U/kg of the protease inhibitor resulted in partial inhibition of myocardial reperfusion injury. Moreover, cardiac myeloperoxidase activity in the ischemic myocardium, a marker of neutrophil accumulation, was significantly reduced after aprotinin treatment. Histologic analysis of the reperfused myocardium demonstrated reduced polymorphonuclear leukocyte infiltration and reduced tissue injury. Furthermore, aprotinin treatment resulted in decreased induction of cardiac myocyte apoptosis compared with that seen in vehicle-treated rats.

CONCLUSIONS

Inhibition of serine proteases with aprotinin appears to be an effective means of preserving ischemic myocardium from reperfusion injury, even after 24 hours of reperfusion. Aprotinin might exert cardioprotection through inhibition of polymorphonuclear leukocyte-induced myocardial injury and inhibition of reperfusion-induced apoptosis of cardiac myocytes.

The relative rapidity of recanalization induced by recombinant tissue-type plasminogen activator (r-tPA) and TNK-tPA, assessed with enzymatic methods

BACKGROUND

Comparison of different plasminogen activators is difficult because conventional endpoints such as mortality are relatively insensitive to potential differences in efficacy with respect to rapidity of recanalization of infarct-related arteries.

METHODS

This study was performed to determine whether valid comparisons could be made by means of biochemical endpoints that have been demonstrated previously to permit estimation of the time of opening of an infarct-related artery in experimental animals and in patients. The method is based on time-dependent interconversion of isoforms of creatine kinase mediated by carboxypeptidase N, an enzyme present in excess in circulating blood. A small subset of 39 patients studied in the ASsessment of the Safety and Efficacy of a New Thrombolytic agent (ASSENT-2) trial were evaluated to determine the feasibility of using the creatine kinase isoform method for comparison of two tissue-type plasminogen activators (tPA), recombinant tPA (r-tPA) and TNK-tPA.

RESULTS

Early recanalization (within 40 min of the onset of treatment with the plasminogen activator) occurred in 56% of patients treated with r-tPA and 76% of those treated with TNK-tPA.

CONCLUSIONS

Differences in the efficacy of plasminogen activators with respect to rapidity of recanalization appear to be readily detectable by means of assaying creatine kinase isoforms in serially acquired blood samples under conditions that permit widespread application of the approach developed.

Myonecrosis after revascularization procedures

The detection of elevated cardiac enzyme levels and the occurrence of electrocardiographic (ECG) abnormalities after revascularization procedures have been the subject of recent controversy. This report represents an effort to achieve a consensus among a group of researchers with data on this subject. Creatine kinase (CK) or CK-MB isoenzyme (CK-MB) elevations occur in 5% to 30% of patients after a percutaneous intervention and commonly during coronary artery bypass graft surgery (CABG). Although Q wave formation is rare, other ECG changes are common. The rate of detection is highly dependent on the intensity of enzyme and ECG measurement. Because most events occur without the development of a Q wave, the ECG will not definitively diagnose them; even the ECG criteria for Q wave formation signifying an important clinical event have been variable. At least 10 studies evaluating > 10,000 patients undergoing percutaneous intervention have demonstrated that elevation of CK or CK-MB is associated not only with a higher mortality, but also with a higher risk of subsequent cardiac events and higher cost. Efforts to identify a specific cutoff value below which the prognosis is not impaired have not been successful. Rather, the risk of adverse outcomes increases with any elevation of CK or CK-MB and increases further in proportion to the level of intervention. This information complements similar previous data on CABG. Obtaining preprocedural and postprocedural ECGs and measurement of serial cardiac enzymes after revascularization are recommended. Patients with enzyme levels elevated more than threefold above the upper limit of normal or with ECG changes diagnostic for Q wave myocardial infarction (MI) should be treated as patients with an MI. Patients with more modest elevations should be observed carefully. Clinical trials should ensure systematic evaluation for myocardial necrosis, with attention paid to multivariable analysis of risk factors for poor long-term outcome, to determine the extent to which enzyme elevation is an independent risk factor after considering clinical history, coronary anatomy, left ventricular function and clinical evidence of ischemia. In addition, tracking of enzyme levels in clinical trials is needed to determine whether interventions that reduce periprocedural enzyme elevation also improve mortality.

Cardioprotective effect of interleukin-10 in murine myocardial ischemia-reperfusion

We investigated the cardioprotective effects of rat interleukin-10 in a murine model of myocardial ischemia-reperfusion (20 min ischemia, 24 h reperfusion). Interleukin-10 (100 microg/rat) administered 15 min prior to reperfusion, significantly (P < 0.01) attenuated myocardial injury compared to rats receiving only 0.9% saline as a vehicle, as indicated by a reduced loss of myocardial creatine kinase from the ischemic-reperfused myocardium. Cardiac myeloperoxidase activity was also significantly (P < 0.01) attenuated by interleukin-10 within the ischemic-reperfused region compared to vehicle treated rats. To further investigate the mechanism of interleukin-10 we observed the in vitro adherence of neutrophil to rat vascular endothelium. Interleukin-10 treatment significantly (P < 0.05) attenuated neutrophil adherence to rat superior mesenteric artery endothelium stimulated with interleukin-1beta. Thus, interleukin-10 demonstrated significant cardioprotective effects as evidenced by a decrease in myocardial creatine kinase loss as well as an inhibition of neutrophil accumulation within the myocardium. It appears as though interleukin-10 mediates its effects, at least in part, by inhibiting leukocyte-endothelial interactions.

Reversible myocardial ischemic injury is not associated with increased creatine kinase activity in plasma

Creatine kinase (CK) isoenzymes MM, MB, and BB are located primarily in the cell cytosol, and increased CKMB in plasma is the hallmark of myocardial infarction. However, whether CK is released with reversible ischemic injury remains controversial. Here, we assessed plasma CK activity—cytosolic and mitochondrial CK—in serial samples (every 10 min for 60 min, then hourly or every 4 h for 48 h) from 46 conscious dogs after transient or sustained coronary occlusion. Four dogs were sham-operated (controls); four underwent sustained coronary occlusion (96 h); and 38 underwent transient coronary occlusion (10–40 min) followed by 48 h of reperfusion. In postmortem histological examination of the dogs’ hearts by light and electron microscopy, we looked for ischemia or necrosis. The presence of cell swelling and glycogen depletion was indicative of ischemia, whereas the added presence of cell disruption indicated necrosis. Coronary occlusion for ≥20 min consistently increased plasma mitochondrial and total CK activity and produced histologically evident myocardial necrosis. In contrast, after 10 to 15 min of coronary occlusion, 12 of 14 animals, despite extensive severe reversible ischemia, showed no increase in plasma CK; the remaining 2, which had increased plasma CK, had subendocardial necrosis. Thus, cytosolic or mitochondrial CK is released from the heart only when there has been irreversible myocardial injury—a finding with significant diagnostic and therapeutic implications.

Protection of rat myocardium by mitogenic and non-mitogenic fibroblast growth factor during post-ischemic reperfusion

The effects of acidic fibroblast growth factor (FGF-1) and basic fibroblast growth factor (FGF-2) and a non mitogenic form of FGF1 on myocardial ischemia and reperfusion were assessed. Rats underwent 10 minutes of coronary artery occlusion followed by 24 hours of reperfusion. Creatinine kinase content of the affected myocardium showed that both fibroblast growth factors 1 and 2 effectively protected against ischemia reperfusion injury (p < 0.01), and that the vasoactive but nonmitogenic form of the FGF1 was equally protective (p < 0.01 versus control + vehicle). The results were confirmed by light and electron-microscopy histological studies. Histological evaluations after treatment with the non-mitogenic fibroblast growth factor 1 showed that it did not generate the severe hyperplasia and connective tissue disorganization observed with the native mitogenic proteins. The possibility of using a non-mitogenic form of fibroblast growth factor for cardio-protection circumvents many of the potentially undesirable effects that may derive from systemically introducing broad spectrum acting fibroblast growth factors in vivo. This myocardial protection observed 24 hours after the treatment with fibroblast growth factors, and the efficacy of the non-mitogenic form of the protein, also suggest that the protective effect of fibroblast growth factors may be due to the increased blood flow rather than to angiogenesis.

Variation in serum creatine phosphokinase activity as indicated in two-phase EMC-D virus-induced myocarditis

In this study, myocardial damage in the D-variant of encephalomyocarditis (EMC-D) virus-induced myocarditis has been investigated consecutively by measuring serum creatine phosphokinase (CPK) activity. CPK activity in 8 week-old male BALB/cAJcl mice inoculated with EMC-D virus increased to a peak at 4 or 5 days postinoculation (DPI) and then gradually decreased. The CPK activity rose again after 7 DPI until it reached a second peak. In view of the kinetics of CPK activity, two-phase (early and late phase) myocardial damage in EMC virus infection were considered. In the late phase, an increase in cellular infiltration in the myocardium and a decrease in viral titer in the heart were observed. It was therefore suspected that the increase in CPK in the late phase may be caused by cellular infiltration, but not by viral replication. In our results, we suggested that a serial measurement of serum CPK activity might be a useful method for throwing more light on the myocardial damage caused by the autoimmune response. We also used a pathological (TUNEL) method to detect apoptotic cells and some apoptotic myocytes in the myocardium in late phase EMC virus-induced myocarditis.

Cardioprotective effect of insulin-like growth factor I in myocardial ischemia followed by reperfusion

In the present study, the cardioprotective effects of insulin-like growth factor I (IGF-I) were examined in a murine model of myocardial ischemia reperfusion (i.e., 20 min + 24 hr). IGF-I (1-10 micrograms per rat) administered 1 hr prior to ischemia significantly attenuated myocardial injury (i.e., creatine kinase loss) compared to vehicle (P < 0.001). In addition, cardiac myeloperoxidase activity, an index of neutrophil accumulation, in the ischemic area was significantly attenuated by IGF-I (P < 0.001). This protective effect of IGF-I was not observed with des-(1-3)-IGF-I. Immunohistochemical analysis of ischemic-reperfused myocardial tissue demonstrated markedly increased DNA fragmentation due to programmed cell death (i.e., apoptosis) compared to nonischemic myocardium. Furthermore, IGF-I significantly attenuated the incidence of myocyte apoptosis after myocardial ischemia and reperfusion. Therefore, IGF-I appears to be an effective agent for preserving ischemic myocardium from reperfusion injury and protects via two different mechanisms--inhibition of polymorphonuclear leukocyte-induced cardiac necrosis and inhibition of reperfusion-induced apoptosis of cardiac myocytes.

Myocardial prostacyclin and thromboxane A2 synthetase activities during ischemia and reperfusion in isolated rabbit heart

The aim of the study was to determine the prostacyclin (PGI2) and thromboxane A2 (TXA2) synthetase activities of myocardial tissue and their variation during ischemia and reperfusion. Regional ischemia was induced by 10 min occlusion of the left anterior descending coronary artery in isolated Langendorff rabbit hearts. Biosynthesis of PGI2 and TXA2 were carried out by using arachidonic acid as substrate and left ventricle microsomes (LVM) from ischemic and non-ischemic areas as sources of PGI2 and TXA2 synthetase. 6-keto-PGF1 alpha and TXB2, stable metabolites of PGI2 and TXA2 respectively, were determined by radioimmunoassay. Experiments carried out under the adopted conditions showed that LVM were able to synthetise PGI2 as well as TXA2 from arachidonic acid. On the other hand, ischemia depressed both PGI2 and TXA2 synthetase activities of cardiac tissue: the depression was more pronounced on TXA2 synthetase than on PGI2 synthetase with no significant difference between ischemic and non-ischemic regions. Moreover, ischemia increased the ratio 6-keto-PGF1 alpha/TXB2 indicating therefore that it can facilitate the formation of PGI2. The post ischemic reperfusion of the heart counteracted the decrease in PGI2 synthetase induced by ischemia which returned to the normal level: reperfusion also slightly reversed the decrease in TXA2 the decrease in TXA2 synthetase. However, the diminution in TXA2 synthetase of non-ischemic myocardium was attenuated but it remained lower than the normal level. These results suggested that the whole left ventricle is affected by regional ischemia. Furthermore it appears that myocardial TXA2 synthetase is more vulnerable than PGI2 synthetase to a lack of oxygen and nutrients.

Exercise training, indomethacin, and isoproterenol-induced myocardial necrosis in the rat

It was hypothesized that endurance exercise training would attenuate isoproterenol-induced myocardial necrosis in the rat by increasing the concentration of prostacyclin in the myocardial vasculature. Rats were randomly assigned to exercise and control groups. Exercisers ran on a motorized treadmill 1 h.d-1, 5 d.week-1 for 14 weeks. Immediately following the training program subgroups of rats were injected with 4 mg.kg-1 indomethacin or saline. One day later, all rats were given a subcutaneous injection of isoproterenol (20 mg.kg-1); after another 24 h they were sacrificed. A decrease of myocardial creatine kinase (CK) activity was used as a marker for myocardial necrosis. Endurance exercise training attenuated the isoproterenol-induced decrease in myocardial CK relative to control by approximately 37% (exercise: 16.4 +/- 0.6 U.mg-1 protein; control: 10.5 +/- 0.6 U.mg-1 protein; p less than 0.05). Pretreatment with indomethacin decreased myocardial CK in the exercise-trained rats (indomethacin: 15.4 +/- 0.8 U.mg-1 protein; saline: 17.7 +/- 0.7 U.mg-1 protein; p less than 0.05), but not in the controls (indomethacin: 10.3 +/- 1.0 U.mg-1 protein; saline: 10.8 +/- 0.6 U.mg-1 protein; p greater than 0.05). The concentration of myocardial 6-keto-PGF1 alpha, a marker for prostacyclin, was not altered by exercise but, as expected, was reduced by indomethacin pretreatment (p less than 0.05). Thus, exercise training reduces myocardial damage caused by isoproterenol, but the evidence does not support the hypothesis that prostacyclin mediated this effect of training. Further research is needed to determine the extent to which exercise training-induced alterations in sensitivity to PGI2 or TXA2 affect myocardial damage from isoproterenol.(ABSTRACT TRUNCATED AT 250 WORDS)

Mediation of cardioprotection by transforming growth factor-beta

Myocardial ischemia causes heart injury that is characterized by an increase in circulating tumor necrosis factor (TNF), the local production of superoxide anions, the loss of coronary vasodilation (relaxation) in response to agents that release endothelial cell relaxation factor, and cardiac tissue damage. Ischemic injury can be mimicked by TNF. When given before or immediately after ischemic injury, transforming growth factor-beta (TGF-beta) reduced the amount of superoxide anions in the coronary circulation, maintained endothelial-dependent coronary relaxation, and reduced injury mediated by exogenous TNF. Thus, TGF-beta prevented severe cardiac injury, perhaps by alleviating damage mediated by increases in circulating TNF.

Cardiovascular effects of acute hypercholesterolemia in rabbits. Reversal with lovastatin treatment

Hypercholesterolemia was induced in New Zealand white rabbits by feeding them a 0.5% cholesterol-enriched rabbit chow for 2 wk. Half of the cholesterol-fed rabbits were given lovastatin, a potent inhibitor of hydroxymethylglutaryl-coenzyme A reductase (HMG-CoA reductase), the rate limiting enzyme in cholesterol biosynthesis, and the other half were given its vehicle (i.e., DMSO). At the end of 2 wk, the rabbits underwent experimental myocardial ischemia or a sham ischemia procedure. Ischemic animals fed the cholesterol-enriched diet for 2 wk experienced much greater cardiac damage than ischemic rabbits fed the control diet, despite the absence of any atherosclerosis. Lovastatin was shown to protect the ischemic rabbit myocardium by three different indices of ischemic damage: (a) maintenance of creatine kinase (CK) activity in the ischemic myocardium; (b) reduced loss of free amino-nitrogen containing compounds from the ischemic myocardium; and (c) blunting the rise of plasma CK activity. These effects were not due to differences in myocardial oxygen demand between the groups. Arteries isolated from animals fed the cholesterol-enriched diet developed defects in endothelium-dependent relaxation in both large vessels as well as coronary resistance vessels. Acute hypercholesterolemia increases the severity of myocardial ischemia while at the same time impairing endothelium-dependent relaxation. These deleterious changes can be significantly attenuated by treatment with lovastatin.

Hemodialysis with calcium-free dialysate prevents myocardial creatine kinase depletion after brief coronary artery occlusion in dogs

To evaluate the effect of hypocalcemia on myocardial creatine kinase (CK) depletion after brief coronary artery occlusion and reperfusion, dogs were rendered hypocalcemic via systemic hemodialysis for eighty minutes in the absence of Ca. Control animals were hemodialysed in the presence of Ca. The left anterior descending coronary artery was then occluded for six minutes and reperfusion for eighty minutes occurred at low flow of dialysate. A 50% decrease in serum Ca of the hypocalcemic animals during the eighty minutes of hemodialysis resulted in a significant (about 35%) decrease of myocardial Ca. Comparison of the myocardial creatine kinase activity following reperfusion showed preservation of the enzyme in the ischemic areas of the hypocalcemic animals, whereas the CK activities of the ischemic areas of the normocalcemic animals were much lower (p less than 0.005). During the reperfusion period serum Ca of the hypocalcemic group increased to 75% of that of the normocalcemic group while myocardial Ca of both ischemic and nonischemic areas reequilibrated to normocalcemic values. Hemodynamic parameters during the various phases of the experiment were not altered significantly. It is concluded that transient decrease of myocardial Ca produced by hypocalcemia prior to occlusion leads to protection against myocardial damage after brief coronary ligation.

Vascular sympathetic nerve function in congestive heart failure

To determine if intrinsic abnormalities of sympathetic nerve function might contribute to enhanced vascular tone in congestive heart failure, chronic myocardial infarction (infarct) was produced in rats by coronary artery ligation 9 to 10 months previously for comparison with animals subjected to sham operation (sham). The excised pulmonary artery, preincubated with 3H-norepinephrine (NE) was superfused, and stimulated electrically at 2, 4, 8 and 16 Hz. The nonnormalized data at each frequency for electrically evoked 3H overflow in excess of basal outflow was similar in sham and infarct vessels (difference not significant); however, the shape of the frequency-response curves was different. The 3H overflow/pulse from sham vessels was constant between 2 and 16 Hz; however, for the infarct vessels there was a significant reduction (p less than 0.05) at the highest frequency (16 Hz). Because of an 18.4% lower peak 3H overflow at 16 Hz (difference not significant), the infarct frequency-response curve shifted significantly (4 and 8 Hz, p less than 0.025 and p less than 0.01) to the left when data were expressed as a percent of peak percent 3H overflow, suggesting an increased sensitivity of the system. These data suggest that an intrinsic vascular sympathetic nerve abnormality is not a major cause of the increased plasma NE in congestive heart failure; increased nerve activity or decreased clearance of NE may be more important.

Sarcolemmal phospholipid fatty acid composition and permeability

In this study, the mechanism of ischaemia-induced increased sarcolemmal permeability, as manifested by release of intracellular enzymes, was investigated. The role of changes in the sarcolemmal phospholipid bilayer in this process was evaluated by experimental modulation of the phospholipid fatty acid composition. The isolated perfused rat heart subjected to low-flow hypoxia, was used as a model of global ischaemia. Glucose as well as saturated (palmitate) and unsaturated (linoleate) long-chain fatty acids were used as substrates. Hearts perfused with palmitate or linoleate (1.5 mM, fatty acid/albumin ratio, 3.4) showed a significantly higher rate of lactate dehydrogenase release in both control and ischaemic conditions than hearts perfused with glucose (10 mM). Lactate dehydrogenase release in the fatty acid-perfused hearts was associated with a significant increase in the percentage unsaturation of the sarcolemmal phospholipid fatty acids. Glucose-perfused hearts, on the other hand, showed only minor changes in the sarcolemmal phospholipid fatty acid composition. Attempts to correlate enzyme release directly with an increase in the percentage unsaturation of phospholipid fatty acids failed, since enzyme release was also stimulated in control fatty-acid-perfused hearts which (when compared with glucose) contained a higher percentage saturated phospholipid fatty acids. The results suggest that myocardial ischaemia, apart from changes in the sarcolemmal phospholipid fatty acid composition, also induces several other changes in sarcolemmal composition (e.g., cholesterol loss) which may affect is permeability for macromolecules.

Compromise of beneficial effects of reperfusion on myocardium supplied by vessels with critical residual stenosis

Coronary thrombolysis in patients frequently unmasks high grade residual stenosis. To determine whether beneficial effects of reperfusion are compromised by critical residual coronary stenosis, 14 dogs were instrumented with an external left anterior descending coronary artery balloon occluder, Doppler flow probe and adjustable screw clamp. In eight of the dogs, critical stenosis (abolition of reactive hyperemia after a 20 s occlusion; 95.7 +/- 1.0% cross-sectional area reduction) was induced before occlusion and maintained. In the control group (n = 6), no stenosis was induced. Each dog was subjected to 2 h of myocardial ischemia followed by balloon deflation and 24 h of reperfusion. Myocardial blood flow assessed with microspheres was similar during balloon inflation in both groups and indicative of profound ischemia. Transmural blood flow to the reperfused zone assessed 1 min after balloon deflation was significantly greater in control dogs without residual stenosis (383% of normal compared with 120% of normal in dogs with stenosis) (p less than 0.01). Compromise of transmural flow persisted in dogs with stenosis (85% compared with 121% of normal in control dogs after 1 h, p less than 0.05; and 49% compared with 68% after 24 h of reperfusion, p less than 0.05). Diminution of subendocardial blood flow after reperfusion was particularly marked. The extent of infarction was greater in the heart of dogs with residual stenosis. Thus, residual critical coronary stenosis compromises nutritional perfusion and salvage of reperfused myocardium after recanalization. These observations underscore the need for prompt identification of patients with high grade residual stenosis early after coronary thrombolysis and the potential value of angioplasty or coronary surgery in selected patients soon after initial recanalization.

Myocardial infarction and risk region relationships: evaluation by direct and noninvasive methods

Optimal quantitation of myocardial infarction requires resolution of the three-dimensional geometry of the ischemic region at a time that progression of tissue necrosis has been completed and can be sharply delineated from noninfarcted myocardium but before significant remodeling of the ventricular chamber. Although this can be achieved at two to three days after coronary occlusion by histologic techniques, a variety of technologies including two-dimensional echo, CTT, SPECT, PET, and NMR have demonstrated potential for providing noninvasive quantitative measurements of the extent of myocardial infarction. Additional studies are needed to clarify the utility of these technologies for resolving the highly variable transmural distribution of infarction that is present in the clinical setting. Assessment of the region at risk for infarction, the ischemic zone, requires quantitative measurements of the degree of ischemia as well as the size of the ischemic region. Although the above technologies may provide quantitative measurements of the dimensions of the ischemic zone, the utility for resolving the highly variable transmural distribution of regional myocardial blood flow using clinically applicable methodologies has not been convincingly established at present. It is possible that cine CT, new generation PET, and NMR technologies may eventually provide noninvasive quantitative measurements of regional myocardial blood flow.

Prevention by amiodarone of phospholipid depletion in isoproterenol-induced ischemia in rats

This work was performed to study phospholipid metabolism in isoproterenol-induced ischemic heart and the possible protective effect of amiodarone (Am) and chlorpromazine (CPZ). Heart weight increased 24 h after subcutaneous injection of isoproterenol (40 mg/kg) whereas myocardial phospholipid content and creatine kinase activity decreased without modification of the cholesterol content. The phospholipid content was significantly correlated with creatine kinase activity (P less than 0.001). Phosphatidylcholine, phosphatidylethanolamine and cardiolipin decreased significantly (P less than 0.001) in the isoproterenol group whereas the lysophosphatidylcholine and lysophosphatidylethanolamine content increased. The lysophosphatidylcholine/phosphatidylcholine and lysophosphatidylethanolamine/phosphatidylethanolamine ratios consequently increased to a significant degree (P less than 0.01) suggesting indirectly the activation of phospholipases A in the ischemic myocardium. Free fatty acid content increased, indicating hydrolysis of phosphatidylcholine, phosphatidylethanolamine, lysophosphatidylcholine and lysophosphatidylethanolamine. Intravenous injection of Am (20 mg/kg) or intraperitoneal injection of CPZ (30 mg/kg) prior to isoproterenol injection provided complete protection against phospholipid depletion and against increase of the lysophosphatidylcholine/phosphatidylcholine and lysophosphatidylethanolamine/phosphatidylethanolamine ratios which returned to control values. Neither substance had any effect on the heart weight increase due to an edematous and inflammatory process. The total protection by both substances against phospholipid depletion was not sufficient to prevent the creatine kinase activity decrease. The improved phospholipid degradation in the ischemic myocardium is discussed in relation to the in vitro inhibitory effect of Am or CPZ on phospholipases A activity.

Methods for the metabolic quantification of regional myocardial ischemia

An adequate balance between oxygen supply and demand is a basic requirement for normal cardiac function. When oxygen supply does not meet the demand, progressive cellular damage occurs leading to cardiac dysfunction and, ultimately, tissue death. While traditionally "ischemia" has been defined as decreased oxygen supply secondary to a decrease in blood flow, and "hypoxia" as decreased oxygen supply secondary to a decrease in oxygen tension, this review defines ischemia in its broader sense, namely as a pathophysiologic state in which there is a lack of oxygen relative to the demand for it. In a large number of experimental studies involving the heart, there is need to promptly recognize the ischemic state, to monitor its course in vivo, and to quantify it. Because of cardiac autoregulatory mechanisms, research methods which attempt to quantify supply (e.g., measurement of myocardial blood flow) and/or demand (e.g., measurement of myocardial oxygen consumption) do not necessarily reflect the status of the balance between supply and demand. An imbalance between myocardial supply and demand is more likely to be reflected by metabolic fluxes and by the accumulation of products specific to the ischemic state. Thus, the purpose of this review is to summarize the various methods available to the cardiac surgical investigator today for the metabolic quantification of myocardial ischemia. Due to the complexity of the heart and its inherent regional differences, myocardial ischemic changes are frequently regional in nature. Thus, this review will address metabolic methods for the regional quantification of myocardial ischemia.

Importance of coronary collateral circulation for kinetics of serum creatine kinase in acute myocardial infarction

The effect of coronary collateral perfusion on the kinetics of creatine kinase (CK) was examined in 32 patients undergoing intracoronary thrombolysis within 6 hours after the onset of a first acute myocardial infarction (AMI). Blood sampling for CK was performed every 2 to 4 hours for a period of 72 hours after AMI. The cumulative CK release was determined using the integrated appearance function curve with the individual disappearance rate. In 19 patients in whom thrombolysis was successful (group A), time to peak CK level was 11 +/- 1 (standard error of the mean) hours after AMI and cumulative CK release was 2,599 +/- 424 U/liter. In 6 patients who had a significant collateral circulation to the infarct-related coronary artery and unsuccessful reperfusion (group B), the time to peak CK was 16 +/- 1 hours (p less than 0.05 compared with group A) and cumulative CK release was 1,897 +/- 478 U/liter (difference not significant compared with group A). In the remaining 7 patients, with neither recanalization nor significant collateral perfusion group C, time to peak CK was 21 +/- 1 hours and significantly (p less than 0.05) longer than groups A and B. Cumulative CK release (2,707 +/- 776 U/liter) was not significantly different from groups A and B. Thus, collateral perfusion is an important determinant of the CK time-activity curve during AMI. Early peaking of CK levels does not reliably identify spontaneous or drug-induced recanalization of the infarct-related coronary artery.

Increased severity of acute myocardial ischemia in experimental atherosclerosis

We investigated the effects of acute myocardial ischemia (MI) in a rabbit model of atherosclerosis to determine whether atherosclerosis augments the severity of damage produced in the ischemic myocardium. Normal rabbits were fed a control rabbit chow diet or a diet enriched with either 2% cholesterol or 0.5% cholesterol for 10-12 weeks prior to induction of MI. Plasma cholesterol concentrations in the cholesterol-fed rabbits were 1697 +/- 70 mg/dl (2%) and 1056 +/- 51 mg/dl (0.5%) vs. 61 +/- 12 mg/dl for the non-cholesterol-fed rabbits. All rabbits were observed for 5 h following induction of MI or sham MI. At the conclusion of the experiment, tissue biopsies from the MI region and non-MI (NMI) regions were taken and analyzed for two indicators of the severity of MI--myocardial creatine kinase (CK) activity and free amino-nitrogen concentration. Atherosclerosis was confirmed histologically in coronary artery and aortic specimens. No difference was found among any group with respect to heart rate (HR), mean arterial blood pressure (MABP), or pressure-rate index (HR x MABP/1000, a measure of myocardial oxygen demand). Myocardial CK loss (NMI - MI) was significantly greater for the 2% and 0.5% cholesterol groups (7.3 +/- 1.3 and 4.9 +/- 0.7 IU/mg protein, respectively, P less than 0.05) than in the nonatherosclerotic group (2.5 +/- 0.4 IU/mg protein; P less than 0.001 for 2% and P less than 0.01 for 0.5%). Increased severity of MI was confirmed by a significantly greater myocardial loss of free amino-nitrogen (NMI - MI) in the two atherosclerotic groups.(ABSTRACT TRUNCATED AT 250 WORDS)

A comparison of cumulated CK release with three vectorcardiographic methods of estimating myocardial infarct size

Infarct size estimated by three vectoracardiographic methods was compared with cumulated CK release in 66 patients admitted to hospital within five hours after onset of myocardial infarction. Infarctional changes in the QRS complex were sequentially computed from a continuous 24-hour recording of Frank lead VCG by: (I)-the integrals of QRS vector differences (QRS-VD) relative to the first recording obtained after hospitalization, (II)-the integral of spatial magnitude during the period of initial abnormal depolarization (IAD), (III)-The sum of R-wave amplitude in leads X and Y and Q-wave amplitude in lead Z (sigma R). From the time-trend curves of cumulated CK release, QRS-VD, IAD and sigma R terminal plateau levels were visually determined representing estimated infarct size (ISCK, ISQRS-VD, ISIAD and IS sigma R). The correlation coefficients were: between ISCK and ISQRS-VD r = 0.62, p less than 0.001, ISCK and ISIAD r = 0.22, p = NS, ISCK and IS sigma R r = -0.22, p = NS. The correlation for ISQRS-VD was significantly better than for ISIAD (p = 0.011) and IS sigma R (p = 0.005). The IAD time-trend curves were inconsistent, falling in 24 and rising in 24 patients. For sigma R the corresponding figures were 56 and 10 patients. Thus, neither IAD nor sigma R have been shown to predict infarct size correctly at an early stage or to describe infarct evolution adequately.(ABSTRACT TRUNCATED AT 250 WORDS)

Enhancement of salvage of reperfused ischemic myocardium by diltiazem

Concomitant use of pharmacologic agents may be required for maximal salvage of ischemic myocardium by reperfusion. Accordingly, in dogs with induced thrombotic coronary occlusion, the effects of intravenous diltiazem given 30 minutes before administration of streptokinase on myocardial blood flow and myocardial salvage were evaluated. Two independent types of end points were employed. Positron emission tomography was utilized for noninvasive assessment of myocardial perfusion and infarct extent. Direct measurements included quantification of myocardial infarction by assay of creatine kinase activity in myocardial homogenates. Infarct extent averaged 27.9 +/- 11.4% of left ventricular weight in 10 control dogs in which coronary occlusion was maintained for 24 hours. In eight dogs given streptokinase alone, the infarct extent averaged 16.7 +/- 10.0% of left ventricular mass (p less than 0.05 versus control). In nine other dogs given diltiazem (15 micrograms/kg per min continuously until death was induced) beginning 30 minutes before streptokinase, infarct extent averaged 9.4 +/- 6.7% of left ventricular mass (p less than 0.05 compared with reperfusion alone). At the dose administered, diltiazem did not alter blood flow, heart rate or mean arterial pressure after coronary occlusion or thrombolysis. The region at risk, determined in 16 dogs from perfusion images obtained with positron tomography and oxygen-15-labeled water after coronary occlusion, was similar in the three groups (30.6 +/- 7.3% of the left ventricle in six control dogs, 31.8 +/- 4.5% in five dogs with reperfusion alone and 30.5 +/- 11.6% in five dogs with reperfusion plus diltiazem). Infarct size quantified in terms of the extent of myocardium exhibiting less than 50% of peak carbon-11-labeled palmitate uptake 24 hours after occlusion and expressed as the percent of the region at risk averaged 89.6 +/- 11.4% in control dogs, was significantly reduced to 45.1 +/- 29.8% in dogs with reperfusion alone and was reduced further to 22.3 +/- 16.4% in dogs given diltiazem and reperfusion. Thus, concomitant treatment with diltiazem markedly enhances salvage of reperfused myocardium after coronary thrombolysis.

Streptokinase alters myocardial creatine kinase depletion after ischaemia and reperfusion in rabbits

The efficacy of streptokinase as an intracoronary thrombolytic agent is well-recognized. The effect of streptokinase, distinct from its thrombolytic action, on ischaemic myocardium distal to an area of coronary artery occlusion when reperfusion occurs has not been well-defined. In order to do this, myocardial creatine kinase depletion and the histopathology of infarctions produced in rabbits after 1 h of circumflex coronary artery occlusion and mechanical release of the occlusion were assessed. Streptokinase or saline was infused intravenously for 1 h beginning 0.5 h after occlusion. Rabbits were divided into two time intervals: early (less than 10 h) and late (24 h) after release of coronary artery occlusion. When streptokinase was infused in early infarctions, haemorrhage did not correlate with infarction cross-sectional area or myocardial creatine kinase depletion. However, myocardial creatine kinase depletion was 40% less when streptokinase was infused than when saline was infused, suggesting that streptokinase might limit infarct size. In late infarctions, the degree of haemorrhage, infarction cross-sectional area, and myocardial creatine kinase depletion were similar after reperfusion with streptokinase or saline. By 24 h, the beneficial effect of a single dose of streptokinase given early in the course of occlusion-reperfusion myocardial injury was no longer evident in limiting infarct size.

Protective activity of defibrotide against lethal acute myocardial ischemia in the cat

Defibrotide (D) is a natural polydeoxyribonucleotide from mammalian lungs with profibrinolytic and antithrombotic activities. D also has PGI2-stimulating and tissue plasminogen activator (TPA)-releasing activities, but has no anticoagulant properties. The protective effects of D were demonstrated very recently in a model for non-lethal ischemia in the cat. In the experiments reported here Defibrotide was tested in a model for acute myocardial ischemia leading to ventricular fibrillation (VF) and death of the cat. Occlusion of the coronary artery (LAD) at its origin induced VF and death in 17 of 20 control cats. When cats were treated with D (32 mg Kg-1, bolus i.v., + 32 mg Kg-1 h-1, i.v., after LAD occlusion) 19 of 20 animals survived until the end of experiments. D also prevented changes in plasma and myocardial CPK, hemodynamics and ECG. D was compared with a variety of pharmacological agents which are used clinically for specific cardiovascular diseases. The ability of D to promote considerable generation of PGI2 from vascular walls plus its ability to prevent the decreases in CPK-activity and ATP in the myocardial tissue may have roles in its beneficial effects against ischemic heart in the cat. However, the mechanism/s of the substantial protective effect of D against cardiac death has still to be clarified.

Effects of propranolol on myocardial damage resulting from coronary artery occlusion followed by reperfusion

To evaluate the effects of propranolol on myocardial metabolism after coronary reperfusion, serial measurements of myocardial creatine kinase (CK) and calcium (Ca) contents and CK and lactic acid (LA) concentrations in coronary sinus blood were carried out in 33 open-chest dogs. The left anterior descending coronary artery was occluded for 60 minutes and was then reopened. Twelve of the dogs were given propranolol before occlusion. Reperfusion for 30 minutes in dogs with and without propranolol pretreatment resulted in reduced myocardial CK in the ischemic region and rapidly elevated plasma CK and LA. However, when compared with the control group, the propranolol-treated group showed smaller changes in myocardial CK and plasma LA. Myocardial Ca in the ischemic region was significantly higher than that in the nonischemic region in the control group, but not in the propranolol-treated group. It was concluded that propranolol was protective against myocardial damage resulting from coronary occlusion followed by reperfusion.

Usefulness of defibrotide in protecting ischemic myocardium from early reperfusion damage

Defibrotide, a partially depolymerized polydeoxyribonucleotide obtained from mammalian lungs, was found to stimulate prostacyclin (PGI2) production and to possess significant antithrombotic and fibrinolytic activities. The present study was designed to evaluate the actions of defibrotide on feline myocardial ischemia, produced by 3 hours of occlusion of the left anterior descending coronary artery (LAD) and followed by 2 hours of reperfusion. Intravenous administration of defibrotide (32 mg/kg/hour subsequent to a 32 mg/kg bolus injection), beginning 30 minutes after LAD occlusion, resulted in a 60% reduction in loss of CK specific activity from ischemic myocardium at 5 hours, while the nonischemic myocardium remained unaffected. Defibrotide largely antagonized the increase in ST segment during LAD occlusion and prevented the appearance of a Q wave during early reperfusion, which was found in all vehicle-treated cats. Although 2 of 8 vehicle-treated cats died from ventricular fibrillation and another had severe ventricular tachyarrhythmia, none of the defibrotide-treated cats had similar severe changes in the electrocardiogram and all 7 cats survived the 5-hour observation period. Defibrotide had no direct action on general hemodynamic functions. In a separate set of experiments, defibrotide (0.1 mg/ml) produced an 8- to 10-fold stimulation of PGI2 release. The data suggest a remarkable protective potential of defibrotide on reperfusion damage of the ischemic myocardium, which may be associated with a PGI2-related mechanism.

Kinetics of serum creatine kinase and creatine kinase-MB after intracoronary thrombolysis

The kinetics of the activity of total creatine kinase (CK) and creatine phosphokinase isoenzyme muscle-brain were investigated in 48 patients with acute myocardial infarction after successful intracoronary thrombolysis, and compared to the enzyme activities in 17 patients in whom thrombolysis failed. CK activity peaked significantly earlier after a successful thrombolysis than after an unsuccessful attempt: in patients with successful thrombolysis, CKmax = 10.5 +/- 3.7 h and in patients with an unsuccessful attempt, CKmax = 19.3 +/- 5.9 h; p less than or equal to 0.05. The area under the activity time curve after successful thrombolysis was significantly smaller than after unsuccessful thrombolysis: in patients with successful thrombolysis, CK area = 25,255 U/l per day and in patients with an unsuccessful attempt, CK area = 32,602 U/l per day; p = 0.015. There was a negative correlation between the area under the CK serum curve after successful thrombolysis, and the change of regional wall motion at the site of the acute infarct (p less than or equal to 0.05). From the smaller area under the CK curve in patients after successful thrombolysis, and the significant negative correlation of this measurement with regional left ventricular wall motion, we conclude that myocardial salvage after intracoronary thrombolysis can be assessed by serial CK measurements.

Preferential uptake of intravenously administered hyaluronidase (Hyalosidase) by damaged rat myocardium

The induction of myocardial infarction in rats by ligation of the left-anterior coronary artery was confirmed by measurement of increased plasma levels of creatine kinase, aspartate aminotransferase and lactate dehydrogenase. Using this model system it has been established that intravenous administration of 125I-labelled hyaluronidase to rats resulted in a preferential uptake of the enzyme by damaged myocardium as compared to normal heart tissue.

Cardioprotective effects of defibrotide in acute myocardial ischemia in the cat

We investigated the effects of Defibrotide (D), a natural polydeoxyribonucleotide, on acute myocardial ischemia (AMI) in anesthetized cats. A permanent ligature was placed around the left anterior descending coronary artery (LAD) 12-14 mm from its origin. Ventricular fibrillation and death were exceptional and when they occurred the cats were not included in the evaluation. Pretreatment of cats with D, 32 mg Kg-1 h-1, i.v. infusion, maintained throughout the 5 h occlusion period, reduced AMI-ST segment increases and increased the diminished pressure-rate index (PRI). AMI-induced changes in lactate, ATP and CPK in ischemic tissue were prevented by D. PGI2 gave the same results as D. Atenolol prevented the loss of myocardial CPK, but had no favourable effects on lactate and ATP in ischemic tissue. The beneficial effects of D in AMI reported here could be partly attributed to its ability to enhance PGI2 release from vascular walls; D might also relieve ischemia by improvement of local tissue oxygenation, energy supplies and platelet function by its ability to deaggregate platelet clumps.