Evidence for a ceiling of cardioprotection with a nitric oxide donor-induced delayed preconditioning in rabbits

Although extensive attention has been devoted to the window of preconditioning, only few studies investigated the efficacy of preconditioning against ischemia with increasing durations. To date, a "ceiling of protection" has been demonstrated to occur with early preconditioning but nothing is known about delayed preconditioning. Accordingly, the efficacy of a nitric oxide (NO)-donor-induced delayed preconditioning was tested against ischemic insults of increasing duration. Accordingly, 65 rabbits received a 75-min intravenous infusion of either saline (control group), or an NO-donor (S-nitroso-N-acetylpenicillamine) at 3 microg/kg/min (SNAP-3 group) or 30 microg/kg/min (SNAP-30 group). Twenty-four hours later, rabbits randomly underwent either a 15-, 20-, or a 30-min coronary artery occlusion (CAO). Infarct size was assessed after 72-h reperfusion (triphenyltetrazolium chloride staining, percentage of the area at risk). After 15-min CAO, both SNAP-3 and SNAP-30 reduced infarct size compared with control (10 +/- 3, 5 +/- 1 versus 29 +/- 8%, respectively; p < 0.05). After 20-min CAO, significant cardioprotection was only observed with SNAP-30 (29 +/- 4, 21 +/- 6 versus 36 +/- 2% for SNAP-3, SNAP-30 versus control, respectively). After 30-min CAO, both SNAP-3 and SNAP-30 failed to reduce infarct size (48 +/- 2, 50 +/- 5 versus 50 +/- 4% for SNAP-3, SNAP-30 versus control, respectively). In conclusion, this study demonstrates a dose-related ceiling of protection with delayed preconditioning induced by an NO donor. It supports that delayed preconditioning might exert its maximal beneficial effect with early reperfusion and this finding supports the necessary use of different durations of ischemia when investigating cardioprotective strategies.