Cardioprotection by local heating: improved myocardial salvage after ischemia and reperfusion.

BACKGROUND: Previous studies have shown that expression of the inducible 70-kD heat-shock protein (HSP72) by whole-body hyperthermia is associated with protection against ischemia-reperfusion injury. To develop techniques for regional elevation of heat-shock proteins that prevent extracardiac sequelae during whole-body hyperthermia, we sought to determine if local heating of the heart in vivo provides protection against ischemia-reperfusion injury in the rat. METHODS: A thermal probe was used to locally heat rat hearts at two adjacent sites on the epicardial surface of the left ventricle. Rats were subjected to either 30 minutes of sham surgery (control; n = 10) or two local applications of the probe at 42.5 degrees to 43.5 degrees C for 15 minutes each (n = 9). After 4 hours, rats were subjected to 30 minutes of regional ischemia followed by 120 minutes of reperfusion. Hearts were removed and area at risk and infarct area were determined. RESULTS: Localized heat stress resulted in a significant limitation of infarct size in heat-treated animals versus controls (mean +/- standard error of the mean infarct area/area at risk = 4.3% +/- 0.85 versus 19.2% +/- 3.4%; p < 0.005). Western blot experiments confirmed elevated HSP72 expression in left (heated) and right (nonheated) ventricular samples from treated animals (n = 6; left ventricular = 5.5-fold; right ventricular = 3.7-fold) compared with sham-operated controls. Controls treated with the probe at 37 degrees C (n = 4) showed no increases in HSP72. CONCLUSIONS: Local heating of the heart is associated with elevated levels of HSP72 and improved myocardial salvage. The increase in expression of HSP72 is not limited to the heated region, but extends into nonheated regions of the heart as well. This may lead to the development of new techniques that improve methods of myocardial revascularization and heart transplantation procedures.

Thrombin hypothesis of thrombus generation and vascular lesion formation.

Thrombin plays a central role in vascular lesion formation. It is the principal mediator of thrombogenesis, which is interrupted when direct antithrombins (including hirudin and its synthetic peptide analogs), thrombin receptor antagonist peptides, or thrombin generation inhibitors (including active-site inhibited factor VIIa, recombinant tick anticoagulant peptide, and omega-3 fatty acids) are used to block thrombin. Thrombin is also a potent growth factor, initiating smooth muscle cell proliferation at injury sites. In baboons, this reaction is 80% reduced by hirudin (p < 0.01). Thrombin also plays a role in modulating the effects of other growth factors such as platelet-derived growth factor (PDGF). Thus, Phe-Pro-Arg-CH2Cl prevents expression in baboons of PDGF-A mRNA induced by vascular injury due to balloon angioplasty; untreated mechanical injury results in a 3-fold increase in PDGF-A mRNA expression. Thrombin also regulates inflammatory processes, inducing expression both of leukocyte adhesion molecules and of their counterreceptors by endothelium.