Late preconditioning enhances recovery of myocardial function after infarction in conscious rabbits

It is unknown whether late preconditioning (PC) enhances the recovery of le ft ventricular (LV) function after a myocardial infarction. Thus 25 conscio us rabbits were subjected to a 30-min coronary occlusion followed by 28 day s of reperfusion after PC 24 h earlier with either ischemia or nitric oxide donor administration [S-nitroso-N-acetylpenicillamine (SNAP)]. The recover y of wall thickening (WTh) after reperfusion was significantly improved in the ischemic PC and SNAP PC groups compared with controls, both at rest and during dobutamine stress. Interestingly, neither ischemia- nor SNAP-induce d late PC attenuated myocardial stunning from day 1 through day 14. Infarct size was smaller in the ischemic PC and SNAP PC groups compared with contr ols. In all groups, WTh at 28 days was positively and linearly related to t he percentage of viable tissue in the region underlying the ultrasonic crys tal (r = 0.90), indicating that the improvement in LV function after both i schemia-induced and NO donor-induced late PC can be fully explained by the reduction in infarct size; a separate effect of late PC on LV remodeling or LV contractility need not be invoked. In conclusion, in conscious rabbits late PC, induced either by ischemia or pharmacologically, not only limits i nfarct size but also enhances the recovery of LV function after myocardial infarction. This finding has important clinical implications and provides t riphenyltetrazolium chloride-independent evidence that late PC limits myoce llular death after sustained ischemia.