Comparative Effects of Nicorandil, a Nicotinamide Nitrate Derivative, and Nifedipine on Myocardial Reperfusion Injury in Dogs

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Abstract
The effects of the nicotinamide nitrate compound nicorandil (SG-75) and the slow channel calcium entry blocker nifedipine on the recovery of subendocardial segment shortening (% SS) were compared with a vehicle-treated group following 30 min of left anterior descending coronary artery (LAD) occlusion and 3 h of reperfusion. Sonomicrometry was used to determine % SS in ischemic and nonischemic myocardium, and radioactive microspheres were used to determine regional myocardial blood flow. Nicorandil (100-.mu.g/kg bolus followed by 25 .mu.g/kg/min i.v.), nifedipine (10-.mu.g/kg bolus followed by 3 .mu.g/kg/min i.v.), or vehicle (saline) was administered 15 min prior to and throughout the occlusion period. Both drugs produced equivalent decreases in the heart rate .times. systolic pressure product before and during LAD occlusion. In addition, total left ventricular weights, the area at risk, the percent of the left ventricle at risk, and collateral blood flow were similar in all three groups. During coronary occlusion, % SS in the ischemic region was equally depressed in each series and passive systolic lengthening resulted. However, following reperfusion, only the nicorandil-treated animals showed an improvement in myocardial segment function through 3 h of reperfusion as compared with the control group. Transmural myocardial blood flow within the ischemic region during reperfusion returned to control values in all three groups: however, the endocardial/epicardial blood flow ratio (endo/epi) was significantly decreased in the control and nicorandil-treated dogs. In contrast, the endo/epi was greater than the preocclusion control in the nifedipine series during reperfusion. Thus, although the mechanism of action of nicorandil in this model is unknown, the improvement in % SS in the nicroandil-treated group was not related to changes in peripheral hemodynamics or improved regional blood flow, since nifedipine produced similar changes in hemodynamics and resulted in a better recovery of perfusion.

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