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The calpain inhibitor A-705253 and the Na(+)/H(+)-exchange inhibitor Cariporide were studied in isolated perfused rabbit hearts subjected to 60 min occlusion of the ramus interventricularis of the left coronary artery (below the origin of the first diagonal branch), followed by 120 min of reperfusion. The inhibitors were added to the perfusion fluid solely or in combination at the beginning of reperfusion. Hemodynamic monitoring and biochemical analysis of perfusion fluid from the coronary outflow were performed. Myocardial infarct size and area at risk (transiently not perfused myocardium) were determined from left ventricular slices after a special staining procedure with Evans blue and 2,3,5-triphenyltetrazolium chloride. The infarcted area (dead myocardium) was 72.7+/-4.0% of the area at risk in untreated controls, but was significantly smaller in the presence of the inhibitors. The largest effect was seen with 10(-6) m A-705253, which reduced the infarcted area to 49.2+/-4.1% of the area at risk, corresponding to a reduction of 33.6%. Cariporide at 10(-6) m reduced the infarct size to the same extent. The combination of both inhibitors, however, did not further improve cardioprotection. No statistical difference was observed between the experimental groups in coronary perfusion, left ventricular pressure, heart rate, and in the release of lactate dehydrogenase and creatin kinase from heart muscle.

Two novel calpain inhibitors (A-705239 and A-705253) were studied in isolated perfused rabbit hearts subjected to 60-min occlusion of the ramus interventricularis of the left coronary artery (below the origin of the first diagonal branch), followed by 120 min of reperfusion. The inhibitors were added to the perfusion fluid in various final concentrations from the beginning of the experiments before the coronary artery was blocked. Hemodynamic monitoring and biochemical analysis of perfusion fluid from the coronary outflow were carried out. Myocardial infarct size and the area at risk (transiently non-perfused myocardium) were determined from left ventricular slices after a special staining procedure with Evans blue and 2,3,5-triphenyltetrazolium chloride. The infarcted area (dead myocardium) was 77.9+/-2.3% of the area at risk in untreated controls ( n =12). The infarct size was significantly reduced in the presence of both calpain inhibitors. The best effect was achieved with 10 -8 M A-705253 ( n =8), which reduced ( p <0.001) the infarcted area to 49.3+/-3.9% of the area at risk, corresponding to an infarct reduction of 61.8%. No statistical difference was observed between the experimental groups in coronary perfusion, left ventricular pressure, and in the release of lactate dehydrogenase and creatine kinase from heart muscle.

The effects of the novel calpain inhibitor A-705239 were studied in isolated perfused rabbit hearts subjected to 45 min of global ischemia, followed by 60 min of reperfusion. During 15 min of perfusion the inhibitor accumulated in myocardial tissue up to 16 times the concentration in the perfusate. Almost complete recovery and survival of heart function (90%) was seen with an inhibitor concentration of 10(-8) M in the perfusion fluid when the compound was administered prior to ischemia. Left ventricular pressure amplitude and coronary flow showed significantly higher values during reperfusion in the presence of the inhibitor. A-705239 significantly reduced the release of creatine kinase, from 166+/-49 U/l in untreated hearts to 44+/-10 U/l, and diminished the release of lactate dehydrogenase from 118+/-20 U/l in untreated hearts to 63+/-4 U/l. Mitochondrial dysfunction following ischemia and reperfusion was markedly attenuated by the inhibitor. Thus, the state 3 respiration rate only decreased to 4.2 in contrast to 2.6 nmol O2/(min x mg s.w.) in untreated hearts, reflecting a reduced damage of oxidative phosphorylation. Furthermore, in the presence of the inhibitor the inner mitochondrial membranes became less permeable as indicated by a smaller leak respiration. The excellent properties of A-705239 should make this compound a valuable tool for further pharmacological studies.