THE INFLUENCE OF THE TIME PERIOD BETWEEN PRECONDITIONING ISCHEMIA ANDPROLONGED ISCHEMIA ON MYOCARDIAL PROTECTION

Ischemic preconditioning with brief periods of ischemia followed by re perfusion protects the myocardium against a subsequent prolonged ische mic insult. Reperfusion may influence the protection given by ischemic preconditioning by washing out metabolites that are accumulated durin g the preconditioning ischemia. This study was designed to define the duration of reperfusion necessary to provide such protection. Hearts o f anesthetized rats were preconditioned by occlusion of the left coron ary artery for 5 minutes. This was followed by reperfusion for either 1 minute (n = 60) or 30 seconds (n = 6). The hearts were then subjecte d to a sustained occlusion of the left coronary artery for 45 minutes followed by reperfusion for 3 hours. Control (n = 11) hearts were subj ected only to occlusion of the left coronary artery for 45 minutes fol lowed by reperfusion for 3 hours. Infarct size was measured using tetr azolium and expressed as a percentage of the region at risk. After rep erfusion for 1 minute there was a significant reduction in the size of the infarct (32.3 +/- 4.1 %), expressed as a percentage of the zone a t risk, when compared to controls (61.9 +/- 3.5 %) (p < 0.01). However , the protection received by preconditioning was lost when reperfusion was limited to 30 seconds (infarct size 63.4 +/- 3.2%). The results s how that the minimum period of reperfusion required to give protection after preconditioning ischemia lies between 30 seconds and 1 minute.