Although experimental and clinical evidences suggest that endothelin-1(ET-1) may play a pathophysiological role in ischemic heart disease, it is still controversial whether ET-1 produced during myocardial ischemia and reperfusion affects the extent of necrotic myocardium. This study was performed to investigate the role of ET-1 and the effect of ET antagonists in infarct size determination.

Male Wistar rats(260-400g) were anesthetized with pentobarbital(i.p. 50mg/kg) and ventilation was assisted via tracheostomy tube. The heart was exposed by midline incision and the left anterior descending coronary artery was ligated with 6-0 silk suture. The ligature was released after 1 hour and reperfusion was performed for 2 hours. In the first set of experiment, FRI139317(ET-A antagonist) was given as bolus i.v.(3mg/kg) 10 minutes before reperfusion, followed by continuous infusion(total 24mg/kg) throughout reperfusion. In the other protocol, bosentan(ET-A/ET-B antagonist ; 10mg/kg) was given 10 minutes before coronary occlusion as i.v. bolus. At the end of reperfusion, the heart was excised and stained with Evans blue dye(1% w/v) and triphenyltetrazolium chloride(TTC;1%) to distinguish infarct region(not stained by TTC and Evans blue), ischemic but viable myocardium(stained brick-red by TTC but not stained by Evans blue) and nonischemic myocardium(dyed by Evans blue). These three regions of myocardium were separated and weighed for analysis. Infarct size(in percent) was expressed as the ratio of infarct region to ischemic myocardium(i.e. infarct region plus ischemic but viable myocardium).

In the first protocol, infarct region was 57.0 ±3.8% of the ischemic myocardium in control(n=9) and 58.9±4.9% in FR139317 group(n=7) ; The difference was not significant statistically. Likewise, ET-A/ET-B antagonist bosentan given before coronary occlusion did not reduce infarct size significantly ; the ratio was 74.2±3.2% in control(n=7) and 69.5±2.0% in bosentan group(n=7).

ET-A antagonist FR139317, given throughout reperfusion, did not reduce myocardial infarct size in rat. Bosentan(ET-A/ET-B antagonist) given just before coronary occlusion as i.v. bolus also did not reduce myocardial infarct size in rat.