Failure of iloprost to protect the regionally ischemic, reperfused porcine heart

Calpain inhibition reduces infarct size and improves global hemodynamics and left ventricular contractility in a porcine myocardial ischemia/reperfusion model

Calpains, a family of Ca2+-dependent cysteine proteases, are activated during myocardial ischemia and reperfusion. This study investigates the cardioprotective effects of calpain inhibition on infarct size and global hemodynamics in an ischemia/reperfusion model in pigs, using the calpain inhibitor A-705253. The left anterior descending coronary artery was occluded for 45 min and reperfused for 6 h. A bolus of 1.0 mg/kg A-705253 or distilled water was given intravenously 15 min prior to induction of ischemia and a constant plasma level of A-705253 was maintained by continuous infusion of 1.0 mg/kg A-705253 during reperfusion. Infarct size was assessed histochemically using triphenyltetrazolium chloride staining. Macromorphometric findings were verified by light microscopy on hematoxylin-eosin- and Tunel-stained serial sections. Global hemodynamics, including the first derivate of the left ventricular pressure (dP / dtmax), were measured continuously throughout the experiment. A-705253 reduced the infarct size by 35% compared to controls (P < 0.05). Hemodynamic alterations, including heart rate, aortic blood pressure, central venous pressure and left atrial pressure, were attenuated mainly during ischemia and the first 2 h during reperfusion by A-705253. Cardiac function improved, as determined by dP / dtmax, after 6 h of reperfusion (P < 0.003). Our results demonstrate that myocardial protection can be achieved by calpain inhibition, which decreases infarct size and improves left ventricular contractility and global hemodynamic function. Hence, the calpain-calpastatin system might play an important pathophysiological role in porcine myocardial ischemia and reperfusion damage and A-705253 could be a promising cardioprotective agent.

A Na+-H+ exchange inhibitor (SM-20550) protects from microvascular deterioration and myocardial injury after reperfusion

Na+-H+ exchange inhibitors may reduce myocardial damage after reperfusion. However, their effects on microvascular deterioration are not known. We examined the potency of a novel Na+-H+ exchange inhibitor, SM-20550 [ N-(Aminoiminomethyl)-1,4-dimethyl-1H-indole-2-carboxamide methanesulfonate], and its effects on microvascular damage after reperfusion. In an in vitro study, the Na+-H+ exchange inhibiting activity of SM-20550 was about 10 times greater than that of ethylisopropyl amiloride. In in vivo experiments, we occluded the left circumflex coronary artery in 29 dogs for 2 h and then reperfused for 5 h. SM-20550 was administered either before ischemia (n = 11) or before reperfusion (n = 7). Another 11 dogs served as controls. We found that SM-20550 not only improved coronary vasodilator responses to acetylcholine and adenosine after reperfusion, but also reduced infarct size (P < 0.01). Intramyocardial bleeding, which should reflect microvascular damage, was not found in dogs with SM-20550 treatment. Infarct size was correlated inversely with collateral blood flow in control (both, P < 0.01) but not in SM-20550-treated animals. Furthermore, SM-20550 significantly suppressed ventricular fibrillation during both ischemia and reperfusion. These results suggest that protective effects of Na+-H+ exchange inhibitors on reperfused myocardium are due at least in part to microvascular protection.

Time delay of cell death by Na+/H+-exchange inhibition in regionally ischemic, reperfused porcine hearts

Studies in different preparations have suggested that Na+/H+ exchange is one mechanism causally involved in cell death in myocardial ischemia and reperfusion. The time delay of cell death by pretreatment with the Na+/H+-exchange inhibitor HOE642, cariporide (4-isopropyl-3-methylsulphonylbenzoyl-guanidine methanesulphonate), was investigated in regionally ischemic, reperfused porcine hearts. HOE642 (1 mg/kg) was injected intravenously in 14 thoracotomized pigs 10 min before occlusion of the left anterior descending coronary artery (45 min of ischemia, six pigs; 70 min of ischemia, six pigs; 90 min of ischemia, two pigs). Ischemia was followed by 24 h of reperfusion. Six animals (45 min of ischemia) served as controls. Infarct size was determined as a ratio of infarcted (tetrazolium stain, histology) to ischemic myocardium (dye technique), and regional myocardial function was assessed by sonomicrometry. HOE642 did not affect global hemodynamic parameters. In the pretreated group with 45 min of ischemia, HOE642 significantly decreased histochemical infarct size from 51.2 +/- 12.6% (control group) to 13.2 +/- 12% (p < 0.005) and histologic infarct size from 44.5 +/- 9% to 17.1 +/- 7% (p < 0.005). Recovery of regional systolic shortening after 24 h of reperfusion was improved from 2 +/- 6% (control group) to 12 +/- 7% (p = 0.02). In addition, myocardial contracture and increase in heart rate during early reperfusion were attenuated. When ischemia was prolonged to 70 min after pretreatment with HOE642, infarct size, recovery of systolic shortening, myocardial contracture, and increase in heart rate did not differ from those of the control group. Pretreatment with HOE642 increased the tolerance to ischemia/reperfusion by approximately 20-25 min. Inhibition of Na+/H+ exchange appears to be very promising in the clinical treatment of acute myocardial ischemia and reperfusion.

Myocardial protection by Na(+)-H+ exchange inhibition in ischemic, reperfused porcine hearts

BACKGROUND

Studies in isolated myocytes and isolated heart preparations have suggested that Na(+)-H+ exchange is an important mechanism for myocardial ischemia-reperfusion injury. This study was undertaken to determine whether inhibition of Na(+)-H+ exchange limits infarct size and improves regional systolic shortening in regional ischemia and reperfusion in intact pigs.

METHODS AND RESULTS

The left anterior descending coronary artery was occluded in 18 anesthetized and thoracotomized pigs for 45 minutes and then reperfused for 24 hours. As main end points of this study, regional systolic shortening (sonomicrometry) and infarct size (percentage of infarcted to ischemic myocardium) were determined at the end of the experiments. Infarcted myocardium was assessed by histochemistry (tetrazolium stain) and by quantitative histology of one heart slice. The Na(+)-H+ exchange inhibitor Hoe 694 was administered intravenously at a dose of 3 mg/kg in 6 pigs each either 10 minutes before ischemia (group A) or 10 minutes before the onset of reperfusion (group B). Six pigs served as controls (group C). Treatment with Hoe 694 before ischemia decreased histochemical infarct size from 65 +/- 18% (control group) to 13 +/- 8% (P < .01) and histological infarct size from 49 +/- 20% (control group) to 14 +/- 4% (P < .01). Histochemical (55 +/- 19%) and histological (42 +/- 15%) infarct sizes of group B were insignificantly reduced by 15%. Myocardial protection in group A was associated with an attenuated contracture after 10 minutes of reperfusion and an improved regional systolic shortening after 24 hours of reperfusion (group A, 25 +/- 12%; control group, 6 +/- 5%; P = .01). These parameters remained unaffected in group B.

CONCLUSIONS

This study clearly demonstrates that Na(+)-H+ exchange is an important mechanism for cell death in myocardial ischemia and reperfusion in intact pigs; thus, inhibition of this exchange system may prove a promising new strategy in the clinical treatment of myocardial ischemia and reperfusion.

Failure of intravenous metoprolol to limit acute myocardial infarct size in a nonreperfused porcine model

The usefulness of intravenous beta-adrenergic receptor blockade in limiting infarct size when neither reperfusion nor collateral flow occurs is unknown. The effect of intravenous metoprolol on limiting myocardial infarct size was therefore examined in a nonreperfused porcine model. Closed-chest techniques were used to occlude the left anterior descending coronary artery, after which animals were randomized at 20 minutes to receive intravenous metoprolol, 0.75 mg/kg, or placebo. Infarct size examined at 5 hours with Evans blue and triphenyltetrazolium staining techniques was expressed as a percentage of total ventricular myocardium at ischemic risk. This percentage was not significantly different between the groups (84% +/- 5% with metoprolol vs 90% +/- 4% with placebo; p = 0.4). Myocardial infarct size was not significantly decreased at 5 hours by early administration of intravenous metoprolol when the infarct artery remained occluded and collateral flow was minimal.

Effect of epinephrine treatment during late ischemia and early reperfusion on regional myocardial function and infarct size in partially infarcted reperfused porcine hearts

This study investigated whether epinephrine treatment during late ischemia and early reperfusion improves systolic shortening after 45 minutes of reperfusion at the cost of increased infarct size. A model consisting of both stunned and dead myocytes was used. The left anterior descending coronary arteries of 10 control and 10 treated pigs were occluded distally for 40 minutes and then reperfused for 3 days. Regional systolic shortening was determined by sonomicrometry, and infarct size was assessed as the percentage of infarcted (tetrazolium stain) to ischemic (dye technique) myocardium. Intravenous administration of epinephrine was started 10 minutes before the onset of reperfusion (5 micrograms/min) and continued until 45 minutes of reperfusion (mean 18 micrograms/min). Immediately before and during 45 minutes of reperfusion, left ventricular peak pressure, dp/dtmax, and heart rate were significantly increased in the treated animals. After 45 minutes of reperfusion, epinephrine treatment improved systolic shortening of the reperfused myocardium (treated group 9% +/- 8%; control group -1% +/- 6%; p < 0.01). Transient beta-adrenergic stimulation of the reperfused myocardium did not increase infarct size (treated group 57.2% +/- 19%; control group 55.4% +/- 17%). In conclusion, epinephrine treatment during late ischemia and early reperfusion improved systolic shortening after 45 minutes of reperfusion without affecting infarct size.

Postischemic cell death in reperfused porcine hearts is not attenuated by the spin trap agent PBN during early reperfusion

Ischemic, reperfused porcine hearts were used to investigate whether the spin trap agent PBN (N-tert-butyl-alpha-phenylnitrone) attenuates postischemic cell death by scavenging of free radicals. The left anterior descending coronary artery (LAD) was ligated distally in 16 pigs for 45 min and then reperfused for 3 h. PBN (coronary concentration approximately 1 mM) was infused into the LAD of eight pigs during the first 45 min of reperfusion. Electron spin resonance spectroscopy (ESR) was performed to identify free radical adducts in the reperfused coronary venous blood. Regional systolic shortening (SS%) was determined by sonomicrometry. Infarct size was evaluated as the percentage of infarcted (tetrazolium stain) to ischemic (dye technique) myocardium. The transmural ultrastructural degree of myocardial injury as well as myocardial ATP levels were assessed at the end of the experiment. Intracoronary treatment with PBN during early reperfusion did not attenuate myocardial damage. Infarct sizes (control group 59 +/- 19%, treated group 55 +/- 14%), transmural ultrastructural alterations, myocardial ATP concentrations (control group 1.8 +/- 0.3 mumol/mg frozen weight, treated group 1.7 +/- 0.4 mumol/mg) and regional systolic shortening at the end of the experiments (control group -1 +/- 5%, treated group -2 +/- 6% did not differ significantly. Furthermore, under various experimental conditions of spin trapping, free radical adducts could not be identified in coronary venous blood during early reperfusion. The results suggest that the spin trap agent PBN (1 mM) does not affect postischemic cell death in porcine hearts.

Pathophysiology and mediators of ischemia-reperfusion injury with special reference to cardiac surgery. A review

Although necessary for the ultimate tissue survival, reperfusion may paradoxically exacerbate the ischemic injury. Ischemia and reperfusion injury is intimately woven together. The relative role of reperfusion injury is not clarified and probably varies with the ischemic insult: Reperfusion is always preceded by ischemia, and some of the reperfusion-related events may represent a process continuing from the ischemic period; thus the proper designation should be ischemia-reperfusion injury. The reperfusion-related events are: arrhythmias, myocardial stunning with both systolic and diastolic dysfunction, and low reflow and microvascular stunning. Of pathogenetic importance are the mode and speed of reperfusion as well as the initiation of an intracoronary inflammatory reaction during reperfusion, including endothelium-leukocyte interaction, platelets, generation of oxygen free radical, generation and release of arachidonic acid metabolites, platelet activating factor, endothelium derived relaxing factor, endothelins, kinins, and histamine, complement activation, disturbances in calcium homeostasis, and disturbances in lipid and fatty acid metabolism.