HEAT-SHOCK RESPONSE AND LIMITATION OF TISSUE NECROSIS DURING OCCLUSION REPERFUSION IN RABBIT HEARTS

Background. Induction of stress proteins, such as heat-shock protein 71 (HSP71), is associated with cardioprotection in isolated ischemic myocardium. We tested this hypothesis in rabbits pretreated with whole-body hyperthermia and then subjected to 30 or 45 minutes of regional coronary occlusion (CO) followed by 3 hours reperfusion (Rep). Methods and Results. Control rabbits did not undergo whole-body hyperthermia; heat-shocked (HS) rabbits were subjected to whole-body hyperthermia at 42-degrees-C for 15 minutes. Rabbits were allowed to recover from whole-body hyperthermia for 24 or 40 hours and were then subjected to CO/Rep. Heart rate and arterial blood pressure were recorded during the experiments. Area of necrosis (tetrazolium staining) was normalized to anatomic risk zone size (microsphere autoradiography). In rabbits treated with whole-body hyperthermia and 24 hours of recovery, infarct size was significantly reduced in HS rabbits compared with control rabbits (41.2+/-7.8% versus 23.2+/-6.6%; p less-than-or-equal-to 0.05; mean+/-SD) after 30 minutes of CO and 3 hours of Rep. Risk zone size was similar for the two experimental groups. In rabbits treated with whole-body hyperthermia and 40 hours of recovery, infarct size was similar for control and HS animals with either 30 or 45 minutes of CO (p=NS) and 3 hours of Rep. Risk zone size and area of necrosis were similar for these experimental groups. Biopsies from ischemic and nonischemic myocardium were obtained from rabbits at 24 and 40 hours after heat shock and control rabbits to verify expression of HSP71; expression was determined by Western blot analysis. Conclusions. Our findings demonstrate a considerable increase in expression of HSP71 in myocardium from hyperthermia-treated rabbits. Infarct size was significantly reduced after 30 minutes of CO and 3 hours of Rep in hearts at 24 but not 40 hours after heat shock compared with control hearts. We conclude that heat shock-induced cardioprotection is transient and delays the onset of irreversible myocardial injury caused by ischemia.