Preconditioning in Immature Rabbit Hearts

Abstract

Background —The protective effects of ischemic preconditioning have been shown to occur in adult hearts of all species studied. We determined whether immature hearts normoxic or chronically hypoxic from birth could be preconditioned, the time window or memory of the cardioprotective effect, and the involvement of the K _ATP channel. Methods and Results —Isolated immature rabbit hearts (7 to 10 days old) were subjected to 0, 1, or 3 cycles of preconditioning consisting of 5 minutes of global ischemia plus 10 minutes of reperfusion. This was followed by 30 minutes of global ischemia and 35 minutes of reperfusion. Normoxic hearts (F io ₂ =0.21) subjected to 1 cycle of preconditioning recovered 70±7% of left ventricular developed pressure compared with 43±8% recovery in nonpreconditioned controls. Three cycles of preconditioning did not result in additional recovery (63±8%). Hearts from rabbits raised from birth in hypoxic conditions (F io ₂ =0.12) and subjected to 1 and 3 preconditioning cycles did not show increased recovery (68±8% and 65±5%) compared with nonpreconditioned hypoxic controls (63±9%), although the recovery was greater in chronically hypoxic hearts than in age-matched normoxic controls. Increasing the recovery period after the preconditioning stimulus from 10 to 30 minutes resulted in a loss of cardioprotection. Pretreatment of normoxic hearts for 30 minutes with the K _ATP channel blocker 5-hydroxydecanoate (300 μmol/L) completely abolished preconditioning (70±7% to 35±9%) but had no effect on nonpreconditioned hearts (40±8%). Conclusions —Immature hearts normoxic from birth can be preconditioned, whereas immature hearts hypoxic from birth cannot. Preconditioning in normoxic immature hearts is associated with activation of the K _ATP channel.