Failure to confer cardioprotection and to increase the expression of heat-shock protein 70 by preconditioning with a κ-opioid receptor agonist during ischaemia and reperfusion in streptozotocin-induced diabetic rats

Aims/hypothesis. The aim of this study was to determine the effects of preconditioning on injury and expression of heat shock proteins 70 in diabetic rat hearts. Methods. Diabetes was induced by an intraperitoneal injection of 65 mg kg(-1) streptozotocin. Daily subcutaneous injection of 4 IU insulin started 2 weeks after streptozotocin treatment for 4 weeks. Rats were preconditioned by intravenous injection of 10 mg kg(-1) U50,488H, a selective kappa-opioid receptor agonist (U50,488H preconditioning). The effects of U50,488H preconditioning had previously been shown to be blocked by a selective kappa-opioid receptor antagonist, nor-binaltorphimine. Twenty-four hours later, rats were subjected to 30 min of regional ischaemia by occlusion of the left coronary artery followed by 4 h of reperfusion. Infarct size was determined at the end of reperfusion. Stress-inducible and constitutive heat shock proteins 70 were analysed at the end of ischaemia and reperfusion by Western blotting. Results. Myocardial infarcts induced by ischaemia and reperfusion were greater in diabetic rats. U50,488H preconditioning significantly reduced the infarct size and increased the expression of stress-inducible heat-shock protein 70 in normal rats. The effects of U50,488H preconditioning were abolished in streptozotocin-induced diabetic rats, but restored by insulin replacement. Conclusion/interpretation. In addition to a greater susceptibility to ischaemic insults, the delayed cardioprotection of U50,488H preconditioning was lost, which could at least partly be due to impaired synthesis of stress-inducible heat-shock protein 70 in diabetic rats.