Whole body heat stress fails to limit infarct size in the reperfused rabbit heart

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Abstract
Objective: It has recently been shown that induction of heat stress proteins by whole body heat stress confers myocardial protection in the isolated in vitro rat and rabbit heart. This study extends the above studies by examining the effects of stress protein synthesis on the limitation of infarct size in the in vivo rabbit heart model. Methods: 30 male New Zealand white rabbits were used. Six rabbits were used for measurement of heat stress protein; 10 were used for infarct size determination in a heat stress group (HS); 14 were used for infarct size determination in a control group. There were 10 exclusions. Under anaesthesia, body temperature was raised to 42°C for 15 min in the HS group. Following 24 hours of recovery rabbits were reanaesthetised and the hearts subjected to a 45 min period of regional ischaemia followed by 3 h reperfusion. The risk zone was defined with fluorescent particles and the infarct area determined by tetrazolium staining. Western blotting showed an increase in the 72 KD heat stress protein in hearts in the HS group. Results: Infarct size as a percent of risk area was 61.4 (SEM 6.4)% (n=14) in control hearts and 71.8(7.3)% (n=10) in the HS hearts. These results were not statistically significant. Conclusions: No protective effect of heat stress could be seen when infarct size was used as the end point. Either the protection seen in earlier studies using the Krebs perfused isolated heart model does not accurately reflect protection against myocardial infarction, or heat stress itself may induce injurious factors in the blood which will negate any direct protective effect to the myocardium in this model.

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