Reduction in myocardial ischemic/reperfusion injury and neutrophil accumulation after therapeutic administration of streptokinase.

The benefit of thrombolytic agents to reduce myocardial infarct size, improve left ventricular (LV) function, and prolong survival in human subjects is generally recognized, although the precise mechanism is poorly defined. This study was designed to evaluate the cardioprotective effects of streptokinase (SK) in rats, a species less responsive to plasminogen activators, using a model of mechanical occlusion and release of the left coronary artery. Myocardial injury and polymorphonuclear leukocyte (PMN) infiltration were determined by measuring creatine phosphokinase (CPK) specific activity and myeloperoxidase (MPO) activity, respectively, in the LV free wall (LVFW). After coronary artery occlusion for 0.5 h and reperfusion for 24 h (myocardial ischemia, MI/R), CPK specific activity decreased from 7.0 +/- 0.3 U/mg protein in the sham + vehicle group to 5.6 +/- 0.5 U/mg protein in the MI/R + vehicle group (n = 19, p less than 0.01), while MPO activity increased from 0.14 +/- 0.03 U/g tissue in the sham + vehicle group to 2.8 +/- 0.7 U/g in the MI/R + vehicle group (p less than 0.001). Administration of SK (100,000 IU/kg + 50,000 IU/kg/h for 2 h beginning 15 min before coronary artery reperfusion) reduced the loss of CPK specific activity from reperfused myocardium (6.8 +/- 0.5 U/mg protein, n = 23, p less than 0.05 as compared with the MI/R + vehicle group) and attenuated the increase in MPO activity (1.3 +/- 0.4 U/g tissue, p less than 0.05 as compared with the MI/R + vehicle group). This dose of SK did not change plasma fibrinogen concentration, slightly reduced plasminogen activity (i.e., 20% from control value), and markedly reduced alpha 2-antiplasmin activity (i.e., 60% from control values). A lower dose of SK (i.e., 10,000 IU/kg + 5,000 IU/kg/h for 2 h) did not reduce myocardial injury, did not attenuate the increase in MPO activity, and had no effect on the measured hemostatic parameters. Survival in all MI/R groups ranged from 62 to 66%, and there were no differences in survival between any of the groups (p greater than 0.05). In a model of arachidonic acid-induced rat hindpaw inflammation, SK had no effect on the increase in MPO activity, suggesting that the increase in myocardial MPO activity was not due to a direct effect on inflammatory cell accumulation. In in vitro studies, SK (1-1,000 U/ml) did not scavenge superoxide anion produced by purine (10 mM) and xanthine oxidase (10 mU/ml), nor did it reduce superoxide release, beta-glucuronidase release, or neutrophil aggregation of rabbit peritoneal neutrophils activated with fMLP.(ABSTRACT TRUNCATED AT 400 WORDS)     

Effect of propranolol on ischemic myocardial damage and left ventricular hypertrophy following permanent coronary artery occlusion or occlusion followed by reperfusion

This study was designed to assess the effect of propranolol for limiting myocardial damage and hypertrophy in rats with permanent coronary artery occlusion or occlusion followed by reperfusion. Rats were subjected to occlusion of the left main coronary artery for 48 h (MI) or 0.5 h of occlusion followed by reperfusion for 47.5 h (MI/R). Myocardial injury was determined by measuring the depletion of creatine phosphokinase (CK) levels from the left ventricular free wall. In comparison to sham-occluded animals, myocardial CK levels were significantly decreased by 40% in MI + vehicle animals and 30% in MI/R + vehicle animals. Propranolol (0.3 mg/kg 1 min before occlusion followed by 1 mg/kg at 4 and 24 h after occlusion) significantly reduced the loss of myocardial CK-specific activity in MI animals, but failed to prevent the loss of CK-specific activity in animals subjected to coronary artery reperfusion. Left ventricular hypertrophy developed to a similar extent in both vehicle-treated MI and MI/R groups. Propranolol had no effect on the myocardial hypertrophy in MI or MI/R animals. Likewise, in MI/R animals no diminution of polymorphonuclear leukocyte infiltration was seen with propranolol. These data indicate that propranolol had a significant cardioprotective effect in rats with permanent coronary artery occlusion but failed to salvage ischemic tissue, reduce myocardial hypertrophy or mitigate neutrophil infiltration in animals with early reperfusion of the ischemic myocardium. These results suggest that propranolol may afford a significant protection of the ischemic myocardium, but the combination of reperfusion and propranolol may not result in any greater reduction in infarct size than reperfusion alone.     

Reduction of myocardial damage and polymorphonuclear leukocyte accumulation following coronary artery occlusion and reperfusion by the thromboxane receptor antagonist BM 13.505

This study was designed to assess the effect of the thromboxane receptor antagonist, BM 13.505, in limiting myocardial damage and polymorphonuclear leukocyte accumulation in rats subjected to coronary artery occlusion for 30 min with reperfusion for 24 h (MI/R). Myocardial injury and polymorphonuclear leukocyte infiltration were determined by measuring creatine phosphokinase (CPK) specific activity and myeloperoxidase (MPO) activity, respectively, in the left ventricular free wall (LVFW). Myocardial CPK levels were 8.24 +/- 0.33 U/mg protein in sham MI/R-vehicle-treated animals (n = 18), and were significantly decreased to 6.51 +/- 0.44 U/mg protein in MI/R-vehicle animals (n = 22). Myocardial MPO values were 2.4 +/- 0.5 U/g LVFW in sham MI/R animals, and significantly increased to 10.9 +/- 1.3 U/g LVFW in MI/R-vehicle animals. Administration of BM 13.505 (30 mg/kg, i.p.) 1 min prior to coronary occlusion resulted in CPK values of 7.83 +/- 0.45 U/mg protein and MPO levels of 6.1 +/- 0.9 U/g LVFW (p less than 0.05, compared to the MI/R-vehicle group). The survival rate in the MI/R-BM 13.505 group was 74 and 65% at 2 and 24 h, respectively, and was not different from the MI/R-vehicle group. There were no significant differences in mean arterial blood pressure or heart rate between the MI/R-vehicle and MI/R-BM 13.505 groups, indicating that changes in myocardial oxygen demand do not explain the protective effects. A lower dose did not reduce myocardial injury, indicating that the effects of BM 13.505 were dose dependent.(ABSTRACT TRUNCATED AT 250 WORDS)     

Edaravone reduces myocardial infarct size and improves cardiac function and remodelling in rabbits

1. In the present study, we investigated the effect of 3-methyl-1-phenyl-2-pyrazolin-5-one (edaravone), a free radical scavenger, on myocardial infarct (MI) size and cardiac function in an in vivo model of MI in rabbits. We further investigated the contribution of hydroxyl radicals, superoxide and nitric oxide (NO) to its effects. 2. Anaesthetized open-chest Japanese white male rabbits were subjected to 30 min coronary occlusion and 48 h reperfusion. The control group (n = 10) was injected with saline 10 min before reperfusion. The edaravone group (n = 10) was injected with a bolus of 3 mg/kg edaravone 10 min before reperfusion. The edaravone + N(G)-nitro-L-arginine methyl ester (L-NAME) group (n = 5) was given 10 mg/kg, i.v., L-NAME 10 min before the administration of 3 mg/kg edaravone. The L-NAME group (n = 5) was given 10 mg/kg, i.v., L-NAME 20 min before reperfusion. Infarct size was measured using the triphenyl tetrazolium chloride method and is expressed as a percentage of area at risk. Cardiac function was assessed by echocardiography 14 days after infarction. 3. In another series of experiments, rabbits were subjected to 30 min coronary occlusion and 30 min reperfusion and myocardial interstitial 2,3-dihydroxybenzoic acid (DHBA) and 2,5-DHBA levels, indicators of hydroxyl radical, were measured using a microdialysis technique. 4. Infarct size in the edaravone group was significantly reduced compared with that in the control group (27.4 +/- 6.8 vs 43.4 +/- 6.8%, respectively; P < 0.05). The edaravone-induced reduction of infarct size was abolished by pretreatment with L-NAME. Myocardial interstitial levels of 2,3-DHBA and 2,5-DHBA increased 20 and 30 min after ischaemia and peaked at 10 min reperfusion in the control group. Edaravone significantly inhibited the increase in 2,3-DHBA and 2,5-DHBA levels seen during reperfusion. Dihydroethidium staining showing in situ detection of superoxide was less intense in ischaemic myocardium in the edaravone-treated group compared with the control group. Edaravone improved cardiac function and left ventricular remodelling 14 days after infarction. 5. In conclusion, edaravone significantly reduces MI size and improves cardiac function and LV remodelling by decreasing hydroxyl radicals and superoxide in the myocardium and increasing the production of NO during reperfusion in rabbits.     

Reduction in myocardial hemorrhage and the extent of necrosis by gallopamil (D600) in dogs with coronary artery reperfusion.

To determine whether gallopamil (D600), a methoxy derivative of verapamil, administered immediately before coronary artery reperfusion reduces the extent of myocardial hemorrhage and necrosis, the left anterior descending coronary artery was occluded for 3 h and reperfused for 3 h in anesthetized, open-chest dogs. To quantify the extent of the hypoperfused zone (HZ), 99mTc-labeled albumin microspheres were injected into the left atrium 1 min after occlusion. Five minutes before reperfusion, dogs were randomly assigned to a control group or a gallopamil-treated group that immediately after assignment received 0.08 mg/kg gallopamil followed by a continuous infusion of 0.2 mg/kg/h for 3 h. Three hours after reperfusion, the left ventricle was cut into slices for triphenyltetrazolium chloride staining and autoradiography. There were no differences in the extent of the HZ between the two groups. Gallopamil significantly reduced the extent of myocardial necrosis from 81.3 +/- 4.2% (n = 8) of the HZ in the control to 46.1 +/- 13.1% (n = 9, p less than 0.05) in the treated group. The extent of gross hemorrhage was significantly smaller in the gallopamil-treated group (1.3 +/- 0.9% of the left ventricle or 3.1 +/- 1.8% of the HZ, p less than 0.01) as compared with the control group (6.2 +/- 1.4% of the left ventricle or 20.0 +/- 4.6% of the HZ). Thus, gallopamil administered immediately before coronary artery reperfusion limited infarct size and reduced the extent of myocardial hemorrhage.     

Reduction of infarct size and infiltration of polymorphonuclear leukocytes by a thromboxane synthetase inhibitor. Studies in a rabbit ischemic heart model.

The effect of sodium 6-(2-(1-(1H)-imidazolyl)methyl-4,5-dihydrobenzo(b) thiophene)carboxylate (RS-5186), a potent and long acting thromboxane synthetase inhibitor in vitro and in vivo, on infarct size and on the infiltration of polymorphonuclear leukocytes (PMNs), was studied in a rabbit coronary artery occlusion (1 h)--reperfusion (0.5 h or 3 h) model. The infarcted region was stained with triphenyltetrazolium, and the ratio of infarcted area/left ventricular area was calculated. The infiltration of PMNs into the infarcted region was determined by measuring the PMNs specific enzyme, myeloperoxidase (MPO) activity. In the vehicle treated group, infarct size and MPO activity were increased with increased reperfusion time from 0.5 h to 3 h (infarct size: 15.3 +/- 2.7 to 25.2 +/- 3.2%; MPO activity: 255 +/- 51 to 825.3 +/- 169.4 units/g wet weight). There was also a significant correlation (r = 0.90, p less than 0.01) between the infarct size and MPO activity. In contrast, in the RS-5186 treated group (2 mg/kg i.v.), both infarct size and MPO activity did not increase with prolongation of the reperfusion period (infarct size: 12.8 +/- 5.5 to 10.3 +/- 3.6%; MPO activity: 318.8 +/- 36.7 to 381.2 +/- 72.6 units/g wet weight). In 0.5 h reperfused samples, there was no significant difference in infarct size or in MPO activity between the vehicle treated group and RS-5186 treated group.(ABSTRACT TRUNCATED AT 250 WORDS)     

Amelioration of ischemia/reperfusion-induced myocardial infarction by the 2-alkynyladenosine derivative 2-octynyladenosine (YT-146)

The present study was aimed at determining whether the novel adenosine A2-agonist YT-146 may have cardioprotective effects against ischemia-reperfusion injury. Anesthetized open-chest dogs underwent 90-min occlusion of the left anterior descending artery and subsequent 300-min reperfusion. The animals were randomly assigned to receive vehicle, 3, or 10 microg/kg YT-146 or ischemic preconditioning (4 episodes of 5 min occlusion followed by 5 min of reperfusion). Blood pressure, heart rate, and regional myocardial blood flow throughout the experiment were measured, as was the myocardial infarct size after reperfusion. The infarct size of the vehicle-treated dog was 56.2% +/- 2.7% (n = 5), whereas that of 3 or 10 microg/kg YT-146-treated dog was smaller (ie, 29.5% +/- 8.7% or 20.2% +/- 7.0%, respectively; n = 5). The infarct size of the dog treated with 10 microg/kg YT-146 was reduced to a degree similar to that of the ischemic preconditioning (19.2% +/- 6.3%, n = 5). YT-146 at both doses elicited a dose-dependent increase in acute hyperemic coronary flow immediately after reperfusion. The cardioprotective effect may be attributed to the limitation of the infarct size, probably via A2-receptor-mediated coronary artery dilatation during the early period of reperfusion.     

Cardiovascular pharmacology of the adenosine A1/A2-receptor agonist AMP 579: coronary hemodynamic and cardioprotective effects in the canine myocardium

The hemodynamic and cardioprotective properties of the novel adenosine A1/A2 receptor agonist AMP 579 (IS-[1a,2b,3b,4a(S*)]-4-[7-[[1-[(3-chloro-2-thienyl)methyl]propylamino]- 3H-imidazo[4,5-b]pyridin-3-yl]-N-ethyl-2,3-dihydroxy cyclopentanecarboxamide) were studied in two canine models designed to simulate (a) mild single-vessel coronary artery disease, and (b) myocardial ischemia/reperfusion injury. In the first model, a moderate stenosis was placed on the left circumflex coronary artery (LCCA), and the effects of AMP 579 on regional myocardial blood flow were assessed. AMP 579, 10 micrograms/kg/min, i.v., for 10 min, induced coronary dilation without causing endocardial steal. In the model of ischemia/reperfusion injury (60 min LCCA occlusion/5 h reperfusion), AMP 579, 10 micrograms/kg/min, i.v., administered for 15 min before ischemia significantly decreased myocardial infarct size. Control infarct size to area at risk (IS/AAR) equaled 34 +/- 3% (n = 9); IS/AAR for AMP 579-treated dogs equaled 16 +/- 4% (n = 9). Preconditioning (5 min LCCA occlusion + 10 min reperfusion) immediately before the 60-min LCCA occlusion also resulted in a marked decrease in IS/AAR: 9 +/- 3% (n = 6). The selective A1 agonist CPA reduced infarct size when administered at 3 micrograms/kg/min, i.v., for 15 min before LCCA occlusion: IS/AAR = 11 +/- 3% (n = 5). Pretreatment of animals with the adenosine-receptor antagonist 8-SPT, 10 mg/kg, i.v., attenuated the myocardial protective effects associated with preconditioning, CPA, and AMP 579, resulting in IS/AAR values of 28 +/- 7% (n = 7), 28 +/- 4% (n = 8), and 26 +/- 3% (n = 8), respectively. The ability of 8-SPT to block the cardioprotective effects suggests that these effects were mediated through an interaction with adenosine receptors. These experimental results indicate that AMP 579 is an effective coronary vasodilator, which also can protect the heart from ischemic injury. Thus AMP 579 has the potential to be useful in cardiovascular therapeutics.     

Effects of pinacidil on myocardial blood flow and infarct size after acute left anterior descending coronary artery occlusion and reperfusion in awake dogs with and without a coexisting left circumflex coronary artery stenosis

To determine whether partial stenosis of a second major coronary artery promoted vasodilator-induced coronary steal and increased infarct size after acute coronary artery occlusion, we produced acute myocardial infarction by 4-h left anterior descending coronary artery occlusion and 20-h reperfusion in awake dogs with and without a mild to moderate stenosis (33-72%) of the proximal left circumflex coronary artery. Dogs were randomized to receive intravenous (i.v.) normal saline or pinacidil, a new antihypertensive agent with a marked coronary dilator property, beginning 40 min after onset of coronary artery occlusion and continuing throughout the occlusion and the first hour of reperfusion. Pinacidil was titrated to decrease mean aortic pressure 25 mm Hg, which resulted in an increase in heart rate (HR), cardiac output (CO), and left ventricular (LV) dP/dt and LVdP/dt/P. Saline infusion had no effects. Blood flows to ischemic and remote myocardium did not differ between dogs with and without coronary stenosis. Pinacidil increased blood flow threefold in normal myocardium, but had no effect on infarct zone myocardial blood flow or infarct size (58 +/- 4% of region at risk vs. 56 +/- 4% in animals receiving normal saline) in dogs without coronary stenosis. In contrast, similar administration of pinacidil in dogs with coronary stenosis reduced infarct size zone myocardial blood flow and increased infarct size (69 +/- 3% vs. 55 +/- 5% in the saline group, p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of the thromboxane receptor antagonist SQ 29,548 on myocardial infarct size in dogs

The effect of thromboxane A2/prostaglandin endoperoxide receptor blockade on infarct size following myocardial ischemia plus reperfusion was determined in dogs. In anesthetized dogs SQ 29,548 (0.2 mg/kg/h) caused a 1,000-fold shift in the dose flow-response curve of renal and mesenteric beds to U-46619, indicating potent receptor blockade. The vasoconstrictor response of the left circumflex coronary artery (LCX) to U-46619 was completely inhibited by SQ 29,548. Three additional groups of anesthetized dogs were subjected to LCX occlusion and 10 min later were given (a) SQ 29,548 (0.2 mg/kg loading dose + 0.2 mg/kg/h infusion intravenously, i.v., n = 7), a thromboxane A2/prostaglandin endoperoxide receptor antagonist; (b) vehicle (n = 7); and (c) SQ 28,585 (0.2 mg/kg loading dose + 0.2 mg/kg/h infusion i.v., n = 3), an inactive compound structurally related to SQ 29,548. After 90 min of occlusion, the LCX was reperfused for 5 h. The area at risk and infarct size were then determined. The cardiac area at risk was similar in size for all groups. Infarct size as a percentage of the total area at risk was large, 79 +/- 2% in vehicle controls, but this was markedly reduced to 45 +/- 8% with SQ 29,548 treatment. SQ 28,585 did not alter infarct size as compared with vehicle controls. Area at risk and infarct size were highly correlated (r = 0.95) in vehicle-treated animals. None of the drug treatments resulted in a significantly altered hemodynamic status. Thus, blockade of thromboxane A2/prostaglandin endoperoxide receptors during ischemia plus reperfusion resulted in a significant salvage of myocardial tissue and suggests a deleterious role for thromboxane A2 in ischemia.     

Role of protein kinase C, K(ATP) channels and DNA fragmentation in the infarct size-reducing effects of the free radical scavenger T-0970

1. In the present study, we investigated the effect of 1-(3-tert-butyl-2-hydroxy-5-methoxyphenyl)-3-(3-pyridylmethyl) urea hydrocloride (T-0970), a novel water-soluble low-molecular weight free radical scavenger, on the generation of hydroxyl radicals in vivo and on myocardial infarct size in an in vivo model of myocardial infarction in rabbits. 2. T-0970 scavenged hydroxyl radicals generated in the myocardium during reperfusion, as assessed by using a microdialysis technique and HPLC in an in vivo model with 30 min coronary occlusion and 30 min reperfusion in rabbits. 3. Another group of rabbits was subjected to 30 min coronary occlusion and 48 h reperfusion. The control group (n = 10) was infused with saline for 190 min from 10 min before occlusion to 180 min after reperfusion. The treatment group (T-0970 group; n = 10) was injected with a bolus 2.5 mg/kg T-0970 and then infused with T-0970 for 190 min from 10 min before reperfusion to 180 min after reperfusion at a rate of 100 microg/kg per min. The T-0970 + CHE group (n = 5) was given chelerythrine (CHE; a selective inhibitor of protein kinase C (PKC); 5 mg/kg, i.v.) 10 min before the administration of T-0970. The T-0970 + 5-HD group (n = 5) was given 5-hydroxydecanoate (5-HD; an inhibitor of mitochondrial K(ATP) channels; 5 mg/kg, i.v.) 10 min before the administration of T-0970. The CHE and 5-HD groups were given CHE (5 mg/kg, i.v.) and 5-HD (5 mg/kg, i.v.) 20 min before reperfusion, respectively. After 48 h reperfusion, infarct size was measured histologically and expressed as a percentage of the area at risk (AAR). In another series of experiments, the control (n = 5) and T-0970 (n = 5) groups were killed 4 h after reperfusion following 30 min coronary occlusion and DNA fragmentation in myocytes was assessed using in situ dUTP nick end-labelling (TUNEL) at the light microscopic level. 4. Infarct size, as a percentage of AAR, in the T-0970 group was significantly reduced compared with the control group (21+/-4 vs 41+/-4%, respectively; P<0.05). This reduction of infarct size by T-0970 was abolished by pretreatment with CHE and 5-HD. Neither CHE nor 5-HD alone had any effect on infarct size. The percentage of infarcted myocytes with DNA fragmentation by TUNEL in the T-0970 group was significantly reduced compared with the number in the control group (4.0+/-1.5 vs 10.7+/-1.9%, respectively; P<0.05). 5. T-0970, a free radical scavenger, improved reperfusion injury. This effect seemed to be mediated by activation of PKC, the opening of mitochondrial K(ATP) channels and inhibition of DNA fragmentation.     

T-0162, a novel free radical scavenger, reduces myocardial infarct size in rabbits

1. We investigated the effects of 1-(3-tert-butyl-2-hydroxy-5-methoxyphenyl)-3-(3-pyridylmethyl)urea hydrochloride (T-0162), a novel low-molecular weight free radical scavenger, on the generation of superoxide anions and hydroxyl radicals in vitro and in vivo and on myocardial infarct (MI) size in an in vivo model of MI in rabbits. 2. It was found that T-0162 scavenged both superoxide anions and hydroxyl radicals in a concentration-dependent manner in vitro. 3. In an in vivo rabbit model with 30 min coronary occlusion and 30min reperfusion, T-0162 scavenged hydroxyl radicals generated in the myocardium during reperfusion. 4. Anaesthetized open-chest Japanese white male rabbits were subjected to 30 min coronary occlusion and 48 h reperfusion. The control group (n = 10) was infused with 10% lecithin solution for 220 min from 10 min before occlusion to 180 min after reperfusion. The pretreatment group (n = 10) was infused with T-0162 dissolved in 10% lecithin solution for 220 min from 10 min before occlusion to 180 min after reperfusion at a rate of 400 microg/kg per min. The post-treatment group (n = 10) was injected with an i.v. bolus of 10 mg/kg T-0162 and was then infused with 400 microg/kg per min T-0162 for 190 min from 10 min before reperfusion to 180 min after reperfusion. After 48 h reperfusion, infarct size was measured histologically and expressed as a percentage of area at risk (AAR). 5. There was no significant difference in haemodynamic parameters among the three groups throughout the experimental period. The per cent infarct size of the AAR in the T-0162 groups (24.8+/-4.3 and 30.5+/-3.9% for pre- and posttreatment groups, respectively) was significantly reduced compared with control (44.7+/-4.1%; P<0.05). There was no significant difference in the AAR among the three groups. 6. In conclusion, T-0162 reduces MI size through the inhibition of reperfusion injury.     

Tumor necrosis factor alpha, rapid ventricular tachyarrhythmias, and infarct size in canine models of myocardial infarction

Etanercept (2 mg/kg), a TNFalpha sequestrant, was administered 24 hours and 1 hour before LAD coronary artery ligation to examine the role of TNFalpha on lethal ventricular tachyarrhythmias and myocardial necrosis. Dogs treated with etanercept had decreased very rapid (>360 bpm) ventricular triplets (6 +/- 1/h, n = 8) 2 to 24 hours following coronary artery ligation compared with saline (21 +/- 6/h, n = 10, P < 0.05). This was concordant with 8-fold salvage of beta-adrenergic receptor kinase 1 (betaARK) activity compared with control (33.8 +/- 7.2% versus 4.3 +/- 2.2% of unoperated control tissue, P < 0.01, n = 5). Salvage of betaARK occurred without change in the thickness of the epicardial tissue overlying the infarct. In dogs pretreated with etanercept before a 2-hour occlusion/4-hour reperfusion of the LAD coronary artery, infarct mass decreased by 61% (% area at risk) and 55% (% left ventricular mass) in the etanercept group (n = 8) compared with saline (n = 9, P < 0.05). This was concordant with an etanercept-mediated six-fold decrease in leukocyte accumulation within ischemically injured myocardium. TNFalpha antagonism decreases malignant ventricular tachyarrhythmias and may relate to partial protection of normal betaARK-mediated desensitization of beta-adrenergic receptors. TNFalpha sequestration also decreases infarct size in an occlusion/reperfusion model of myocardial ischemia.     

Ranolazine, a partial fatty acid oxidation inhibitor, reduces myocardial infarct size and cardiac troponin T release in the rat

Ranolazine reduces cellular acetyl-CoA content via inhibition of fatty acid beta-oxidation and activates pyruvate dehydrogenase. This metabolic switch increases ATP production per mole of oxygen consumed, reduces the rise in lactic acid and acidosis, and maintains myocardial function under conditions of reduced myocardial oxygen delivery. It is still unclear whether ranolazine causes a reduction of (i) infarct size and (ii) cardiac troponin T release, in a male Wistar rat model of left anterior descending coronary artery occlusion (25 min) and reperfusion (2 h). Rats were subjected to saline infusion (n=12) or ranolazine (bolus injection: 10 mg/kg plus infusion: 9.6 mg/kg/h, n=12), 30 min prior to left anterior descending coronary artery occlusion-reperfusion, respectively. Ranolazine caused a significant reduction in myocardial infarct size of approximately 33% compared to saline control (P<0.05). In addition, infusion of ranolazine significantly attenuated the release of cardiac troponin T into the plasma from 65+/-14 (controls) to 12+/-2 ng/ml. This study demonstrates for the first time that ranolazine significantly reduces (i) infarct size and (ii) cardiac troponin T release in rats subjected to left anterior descending coronary artery occlusion-reperfusion.     

Reduction of myocardial injury by the EP3 receptor agonist TEI-3356. Role of protein kinase C and of K(ATP)-channels

The effects of the prostanoid EP3 receptor agonist TEI-3356 on either protein kinase C or ATP-sensitive (K(ATP)) K+ channels and on the infarct size caused by regional myocardial ischaemia and reperfusion in the rat were investigated. Male Wistar rats (n = 72) were subjected to 25 min occlusion of the left anterior descending coronary artery followed by 2 h of reperfusion. TEI-3356 (1 microg/kg/min i.v., n = 6) caused a significant reduction in infarct size from 60+/-3% (control, n = 8) to 38+/-3% of the area at risk. Pretreatment of rats with 5-hydroxydecanoate (5 mg/kg i.v., n = 6), a specific inhibitor of K(ATP)-channels, attenuated the cardioprotective effects of TEI-3356. The reduction in infarct size afforded by TEI-3356 was also abolished by the protein kinase C inhibitors staurosporine (1 microg/kg i.v., n = 6) and chelerythrine (0.7 mg/kg i.v., n = 5). Thus, TEI-3356 reduces myocardial infarct size in the rat by a mechanism(s) which involves the activation of protein kinase C and the opening of K(ATP)-channels.     

Effects of KR-32570, a new sodium hydrogen exchanger inhibitor, on myocardial infarction and arrhythmias induced by ischemia and reperfusion

The present study was performed to evaluate the cardioprotective effects of [5-(2-methoxy-5-chloro-5-phenyl)furan-2-ylcarbonyl]guanidine (KR-32570) in rat and dog models of coronary artery occlusion and reperfusion. In addition, we sought to clarify the efficacy of KR-32570 on reperfusion-induced fatal ventricular arrhythmia. In anesthetized rats subjected to 45-min coronary occlusion and 90-min reperfusion, KR-32570 (i.v. bolus) dose-dependently reduced myocardial infarct size from 58.0% to 50.7%, 35.3%, 33.5% and 27.0% for 0.03, 0.1, 0.3 and 1.0 mg/kg, respectively (P<0.05). In anesthetized beagle dogs that underwent 1.2-h occlusion followed by 3.0-h reperfusion, KR-32570 (3 mg/kg, i.v. bolus) markedly decreased infarct size from 28.9% in vehicle-treated group to 8.0% (P<0.05), and reduced the reperfusion-induced release in creatine kinase isoenzyme MB, lactate dehydrogenase, Troponin-I and glutamic-oxaloacetic transaminase. KR-32570 dose-dependently decreased the incidence of premature ventricular contraction, ventricular tachycardia or ventricular fibrillation induced by ischemia and reperfusion in rats. Similar results were obtained in dogs with reperfusion-induced arrhythmia. In separate experiments to assess the effects of timing of treatment, KR-32570 given 10 min before or at reperfusion in rat models also significantly reduced the myocardial infarct size (40.9% and 46.1%, respectively) compared with vehicle-treated group. In all studies, KR-32570 caused no significant changes in any hemodynamic profiles. Taken together, these results indicate that KR-32570 significantly reduced the myocardial infarction and incidence of arrhythmias induced by ischemia and reperfusion in rats and dogs, without affecting hemodynamic profiles. Thus, it could be potentially useful in the prevention and treatment of myocardial injuries and lethal ventricular arrhythmias.     

Protective effect of phloroglucinol against myocardial ischaemia-reperfusion injury is related to inhibition of myeloperoxidase activity and inflammatory cell infiltration

1. It has been shown that phloroglucinol has anti-inflammatory and anti-oxidant properties. Both inflammatory cell infiltration and myeloperoxidase (MPO) activation play an important role in myocardial reperfusion injury. The aim of the present study was to explore the effect of phloroglucinol on myocardial reperfusion injury and the mechanisms involved. 2. Anaesthetized rats were pretreated with phloroglucinol (15 or 30 mg/kg, i.g.) or vehicle (5 mmol/L carboxymethyl cellulose sodium) 30 min prior to experimentation. The left main coronary artery was subjected to 1 h occlusion followed by 3 h reperfusion. Infarct size, the release of creatine kinase (CK), inflammatory cell infiltration, MPO activity and protein content, catalase in the blood and myocardium, and myocardial apoptosis were measured. 3. Following myocardial ischaemia and reperfusion in vehicle-treated rats, infarct size was 43.5 ± 3.7% (relative to the area at risk). Accompanying detrimental changes included elevated CK, enhanced inflammatory cell infiltration, high numbers of myocardial apoptotic cells, elevated caspase 3 activity, increased MPO activity and content in the plasma and myocardium and reduced catalase activity. These effects were attenuated by pretreatment with both doses of phloroglucinol (15 and 30 mg/kg, i.g.). 4. The results of the present study suggest that phloroglucinol protects the myocardium against ischaemia-reperfusion injury in rats and that its beneficial effects are related to inhibition of MPO activity and inflammatory cell infiltration.     

Reduction of myocardial infarct size after ischemia and reperfusion by the glycosaminoglycan pentosan polysulfate.

Activation of the complement system contributes to the tissue destruction associated with myocardial ischemia/reperfusion. Pentosan polysulfate (PPS), a negatively charged sulfated glycosaminoglycan (GAG) and an effective inhibitor of complement activation, was studied for its potential to decrease infarct size in an experimental model of myocardial ischemia/reperfusion injury. Open-chest rabbits were subjected to 30-min occlusion of the left coronary artery followed by 5 h of reperfusion. Vehicle (saline) or PPS (30 mg/kg/h) was administered intravenously immediately before the onset of reperfusion and every hour during the reperfusion period. Treatment with PPS significantly (p < 0.05) reduced infarct size as compared with vehicle-treated animals (27.5+/-2.9% vs. 13.34+/-2.6%). Analysis of tissue demonstrated decreased deposition of membrane-attack complex and neutrophil accumulation in the area at risk. The results indicate that, like heparin and related GAGs, PPS possesses the ability to decrease infarct size after an acute period of myocardial ischemia and reperfusion. The observations are consistent with the suggestion that PPS may mediate its cytoprotective effect through modulation of the complement cascade.     

Importance of the flow perfusion deficit in the response to captopril in experimental myocardial infarction.

Previous results on the effects of angiotensin-converting enzyme (ACE) inhibition in myocardial ischemia are conflicting. To determine whether acute ACE inhibition may influence myocardial perfusion deficit during ischemia and reduce ischemia-reperfusion injury, anesthetized open-chest dogs underwent 2-h left anterior descending coronary artery (LAD) occlusion followed by 6-h reperfusion. After 1-h coronary occlusion, each dog was randomized to receive either captopril [5 mg/kg intravenous (i.v.) bolus and 0.25/kg/h infusion for 7 h] or saline. Whereas arterial pressure was reduced (p = 0.001), captopril did not influence myocardial perfusion deficit: Blood flow in the central ischemic zone represented 17.1 +/- 2.8% of the flow in the nonischemic zone versus 20.5 +/- 3.8% before treatment (NS). The values of the control group were 17.8 +/- 2.5 and 16.7 +/- 2.4%, respectively. In addition, there was no difference in infarct size: 35.9 +/- 3.3% of the area at risk in captopril-treated dogs versus 40.0 +/- 3.6% in controls. Analysis of subgroups based on the level of the collateral flow indicated, however, that ACE inhibition had an adverse effect on infarct size in dogs with high collateral flow: 31.9 +/- 4.6% in captopril dogs versus 17.6 +/- 4.7 (p = 0.048). This effect was related to a decrease in collateral flow because animals exhibiting the highest increase in perfusion deficit presented the greatest increase in infarct size (r = -0.92, p = 0.003). Although in dogs with low collateral flow, ACE inhibition appeared to exert a slight beneficial effect on infarct size, we conclude that at least in this dog model, acute ACE inhibition could exacerbate myocardial injury.     

Sulprostone-induced reduction of myocardial infarct size in the rabbit by activation of ATP-sensitive potassium channels.

1. This study examined whether (i) a 1 h pretreatment with or (ii) a continuous infusion of sulprostone reduces myocardial infarct size arising from coronary artery occlusion (60 min) and reperfusion (120 min) in the anaesthetized rabbit. In addition, we investigated whether the observed cardioprotective effect of this selective agonist of prostanoid EP1/EP3 receptors were due to the activation of ATP-sensitive potassium (KATP) channels. 2. In anaesthetized rabbits pretreated with vehicle (5% ethanol in 0.9% saline; 0.05 ml min-1, i.v.) infarct size (expressed as a percentage of the area at risk) after 60 min of coronary artery occlusion followed by 120 min of reperfusion was 59 +/- 4% (n = 10). Pretreatment of rabbits with sulprostone (1.0 microgram kg-1 min-1 for 1 h, discontinued immediately prior to coronary artery occlusion) did not reduce infarct size (60 +/- 4%; n = 4). In contrast, a continuous infusion of sulprostone (1.0 microgram kg-1 min-1) starting 10 min prior to the onset of LAL occlusion and continued throughout the experiment, significantly reduced infarct size (41 +/- 5%, n = 6) when compared to the respective vehicle-treated controls (57 +/- 4%, n = 10; P < 0.05). Sulprostone (pretreatment or continuous infusion) had no effect on any of the haemodynamic parameters measured. 3. The reduction in infarct size afforded by continuous infusion of sulprostone was abolished by pretreatment of rabbits with the KATP channel blocker 5-hydroxydecanoate (5-HD 5 micrograms kg-1; 63 +/- 4%; n = 6). When administered alone, 5-HD had no effect on infarct size when compared to control (52 +/- 6, n = 10). 4. We propose that a continuous infusion of the selective EP1/EP3 prostanoid receptor agonist, sulprostone, reduces infarct size in the anaesthetized rabbit by a mechanism that involves the opening of KATP channels.