Background: Myocardial content of the 70-kd heat shock protein has been found to correlate with improved cardiac recovery after ischemia, but the mechanisms and conditions that regulate its level, particularly under clinical conditions, are unclear. The aim of this study was to assess the effect of hypothermic cardioplegic arrest and reperfusion on the expression of 70-kd heat shock protein in a protocol mimicking conditions of preservation for cardiac transplantation.
Methods: Heat-shocked and control hearts were subjected to 4 hours of cardioplegic arrest and global ischemia at 4 degrees C and then to 20 minutes of reperfusion. Hearts were freeze clamped at different time points-after 15 minutes of Langendorff perfusion, at the end of ischemia, and after 20 minutes of reperfusion, and analyzed for heat shock protein 70 content by Western blotting. Another set of hearts was subjected to 10 minutes of normothermic ischemia and 20 minutes of reperfusion followed by freeze clamping and analysis of heat shock protein 70 content as in cardioplegic arrest protocol. Cardiac function was measured by means of a left ventricular balloon at the end of reperfusion.
Results: Preischemic concentration of 70-kd heat shock protein was increased in heat-shocked hearts compared with control hearts. The content of 70-kd heat shock protein in heat-shocked hearts was further increased from 5.0 +/- 2.4 ng/microg at the end of ischemia to 11.0 +/- 4.9 ng/microg (n = 8, mean +/- SD; P <.05) at 20 minutes of reperfusion after cold cardioplegic arrest. No further rise in 70-kd heat shock protein of the heat-shocked hearts was observed after normothermic ischemia. Maximal developed pressure was 120.8 +/- 13.4 mm Hg in control hearts compared with 164.7 +/- 22.5 mm Hg in heat-shocked hearts (n = 5, mean +/- SD; P =.037) after cardioplegic arrest. By contrast, after normothermic ischemia, maximum developed pressure was 111.2 +/- 10.9 mm Hg in control hearts compared with 139.2 +/- 11.0 mm Hg in heat-shocked hearts (n = 4, mean +/- SD; P =.031).
Conclusion: Hypothermic cardioplegic arrest but not short normothermic ischemia triggered a further increase in the level of 70-kd heat shock protein in heat-shocked rat hearts, which may enhance endogenous cardiac protection.
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