Effect of an orally active Na+/H+ exchange inhibitor, SMP-300, on experimental angina and myocardial infarction models in rats.

The effects of SMP-300, an orally active, potent, and selective Na+/H+ exchange inhibitor, were evaluated and compared with those of nifedipine, propranolol, and nicorandil on three experimental angina models and on myocardial infarction in rats. SMP-300 (0.1-1 mg/kg, p.o.) reduced isoproterenol-induced ST segment depression in a dose-dependent manner. Its maximal effect was comparable to that reported for propranolol and greater than that of nifedipine. SMP-300 (0.3-1 mg/kg) reduced vasopressin-induced ST segment depression in a dose-dependent manner, and its maximal effect was comparable to those of nifedipine and nicorandil. SMP-300 (0.3-1 mg/kg, p.o.) and propranolol (100 mg/kg, p.o.) inhibited coronary artery occlusion-induced T-wave elevation, but nifedipine (3 mg/kg, p.o.) did not. SMP-300 (1 mg/kg, p.o.) reduced myocardial infarct size after 40 min of coronary artery occlusion followed by 24 h of reperfusion, but nifedipine (3 mg/kg, p.o.) or propranolol (100 mg/kg, p.o.) did not. This study provides support for the future use of a Na+/H+ exchange inhibitor as an anti-anginal drug with a novel mode of action.