It is well known that ischemic preconditioning protects the heart against infarction or arrhythmias from a subsequent ischemic injury. Two phases of the effect of preconditioning has been explored, early protection and second window of protection at 24 hours. The late protection was seen in some animal model, but the precise mechanism is controversal. This study was designed to evaluate the late cardioprotective effect and role of HSP70 in ischemic preconditioning of cat heart.

Two groups of cats were studied. Control animals were subjected to an episode of 40-min coronary artery occlusion followed by 30-min reperfusion. Experimental animals were subjected to ischemic preconditioning before the 40-min ishcemia/reperfusion. The preconditioning protocol was comprised of three 5-min episodes of ischemia interspersed by 10-min episodes of reperfusion. After sustained ischemia and reperfusion, left ventricular risk area and infart area were measured by injection of Evans blue bye and triphenyltetrazolium staining, and myocardial HSP70 mRNA was examined in risk(left ventricular anterior wall) and nonrisk(left ventricular posterior wall) area using northern blot hybridization. HSP70 mRNA expression was quantified as a percent of GAPDH. The late cardioprotective effects of ischemic preconditioning were determined by infarct size (% area at risk).

Infarct size was markedly limited by ischemic preconditioning when compared with the control group (18.5±6.9% vs 38.5±11.1%; p<0.001). HSP70 mRNA expression in risk area was much higher in preconditioning group than control group(78±12% vs 41±11%; p<0.01). But, there was no significant difference of HSP70 mRNA expression in the posterior wall between control and ischemic preconditioning group.

These data suggest that ischemic preconditioning have delayed myocardial protective effect from ischemia. The increase in myocardial HSP70 mRNA may be one of the contributing factors to the delayed cardioprotective effects of ischemic preconditioning in cats.