Cardiac stress protein elevation 24 hours after brief ischemia or heat stress is associated with resistance to myocardial infarction.

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Abstract
BACKGROUND To test the hypothesis that the heat shock response is associated with myocardial salvage, the heat stress protein (HSP) content of cardiac tissue was increased by either ischemic or thermal stress. METHODS AND RESULTS Rabbits were divided into four groups. Ischemic pretreatment (n = 15) comprised four 5-minute episodes of coronary ligation separated by 10 minutes of reperfusion. The corresponding control group (n = 21) underwent surgical preparation without coronary ligation. Thermal pretreatment (n = 16) involved whole-body temperature elevation to 42 degrees C for 15 minutes; corresponding controls (n = 15) were treated with anesthetic alone. Twenty-four hours later, hearts were removed for HSP estimation or infarct size assessment after a 30-minute coronary ligation. Myocardial HSP72 content assessed by Western blotting was elevated by both ischemic and thermal pretreatments (2.5 +/- 0.2 units, n = 4, and 2.8 +/- 0.3 units, n = 4, mean +/- SEM; P = NS, respectively) compared with the corresponding control groups (1.0 +/- 0.3, n = 4, P < or = .01 and 0.3 +/- 0.1, n = 4, P < or = .01, respectively). HSP60 was preferentially elevated by ischemic pretreatment. After a 30-minute coronary occlusion and 120 minutes of reperfusion, ischemic and thermal pretreatments limited infarct size as a percentage of the volume at risk by 28.8 +/- 5.2% vs 52.0 +/- 5.2%, P < or = .01 and 32.8 +/- 3.8% vs 56.9 +/- 6.5%, P < or = .01, respectively. CONCLUSIONS Myocardial stress protein induced by either sublethal thermal or ischemic injury is associated with myocardial salvage. Our findings suggest that stress protein elevation, rather than the nonspecific effects of thermal or ischemic stress, may be responsible for the myocardial protection seen in this model. Our observations may have important implications regarding myocardial adaptation to brief periods of ischemia.