Developmental changes in reperfusion injury. A comparison of intracellular cation accumulation in the newborn, neonatal, and adult heart.

Intracellular sodium and calcium accumulation were measured after 30 and 40 minutes of ischemia and 30 minutes of reperfusion in newborn (0 to 7 day), neonatal, (14 to 21 day), and adult (4 to 6 month) New Zealand white rabbit heart preparations. Newborn hearts showed twofold and threefold elevations of calcium when exposed to 30 and 40 minutes of ischemia and reperfusion, respectively, whereas sodium increase was noted only in the 40 minute group. Conversely, adult hearts exhibited sodium elevation if exposed to ischemia for 30 minutes and calcium accumulation occurred only after 40 minutes of ischemia. There was no significant alteration in intracellular sodium and calcium levels after ischemic intervals of 30 and 40 minutes in the neonate. These studies demonstrate that the immature newborn heart is the most susceptible and the neonatal heart is the least susceptible to injury sustained by ischemia followed by reperfusion. These differences in susceptibility to ischemia may be due to age-dependent alterations of intramembrane ionic pumps and channels.