The goal of the study was to determine whether postconditioning protects against different ischemia durations in the rabbit. Rabbits were assigned to a 20-, 25-, 45- or 60-min coronary occlusion followed by 24-h of reperfusion. Rabbits received no further intervention (control) or were postconditioned with four cycles of 30-s occlusion and 30-s reperfusion after myocardial infarction. Plasma levels of troponin I were quantified throughout reperfusion. In control conditions, infarct sizes (% area at risk using triphenyltetrazolium chloride) after 20, 25, 45 and 60 min of coronary occlusions were 23±3, 51±4, 70±3 and 81±3 %, respectively. With 20 and 25 min occlusion, postconditioning reduced infarct size by 43±10 and 73±21 %, respectively. On the other hand, with 45 or 60 min occlusion, postconditioning had no significant effects on infarct size (61±3 and 80±2 % of area at risk). Preconditioning protocol was performed with 25- and 60-min coronary occlusion. As expected, preconditioning significantly reduced infarct size. In conclusion, in the rabbit, the cardioprotection afforded by postconditioning is limited to less than 45 min coronary occlusion.
