Reduction of myocardial infarct size by SM-198110, a novel Na + /H + exchange inhibitor, in rabbits

The effects of 3-[2-({[amino(imino)methyl]amino}carbonyl)-4-chloro-1H-indol-1-yl]-1-propanesulphonic acid monohydrate (SM-198110), a novel potent Na + /H + exchange inhibitor, and cariporide (Hoe642), another Na + /H + exchange inhibitor, were studied in a myocardial ischaemia and reperfusion injury model. Anaesthetized rabbits were subjected to occlusion of the coronary artery for 30 min followed by reperfusion for 5 h. SM-198110 or cariporide was administered before ischaemia and before reperfusion. We also assessed the anti-necrotic effect of SM-198110 when given before reperfusion, both alone and together with glibenclamide, a K ATP channel blocker, 5-hydroxydecanoate (5-HD), a mitochondrial K ATP channel-selective blocker and 8-(p-sulphophenyl)-theophylline (8-SPT), an adenosine receptor blocker. The infarct size was reduced dose-dependently by i.v. administration of SM-198110 before ischaemia, with a significant reduction in serum creatine phosphokinase activity. Infarct sizes, normalized to the size of the area-at-risk (means±SE) were: vehicle 56.6±3.7%; low-dose SM-198110 39.2±6.3%; mid-dose 32.8±7.4% ( P <0.05); high-dose 22.1±6.7% ( P <0.01). This anti-necrotic effect of SM-198110 was achieved without significant haemodynamic changes. Cariporide given before ischaemia also reduced infarct size significantly and dose-dependently. SM-198110 administered before reperfusion also resulted in a dose-dependent reduction in the infarct size. Infarct sizes were: vehicle 56.6±3.7%; low-dose SM-198110 44.5±5.7%; mid-dose 36.3±6.6% ( P <0.01); high-dose 34.7±3.8% ( P <0.01). In contrast, cariporide given before reperfusion did not reduce infarct sizes significantly. The anti-necrotic effect of SM-198110 was observed even when given 10 min after the beginning of reperfusion. Glibenclamide and 5-HD abolished the anti-necrotic effect of treatment before reperfusion with SM-198110. However, the co-administration of 8-SPT with SM-198110 did not affect infarct size. These results suggest that, in addition to Na + /H + exchange inhibition, mitochondrial and/or sarcolemmal K ATP channels contribute to the anti-necrotic effect of SM-198110 when the latter is given before reperfusion.