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Protection by ischemic preconditioning (PC) has not been studied extensively in immature hearts. We studied the developmental differences in the ability of the rat heart to precondition with ischemia.Hearts from 4-, 7-, 14-, and 21-day-old and adult (approximately 50-day-old) rats were aerobically perfused in Langendorff mode before a PC stimulus of either (1) 3-minute ischemia (I), 3-minute reperfusion (R), 5-minute I, 5-minute R, or (2) 4 cycles of 5-minute I and 5-minute R, before a prolonged I (chosen to give 30% to 40% recovery) and 60-minute R. LVDP recovery was expressed as percent of baseline reading (after 20-minute aerobic perfusion). Protection was seen after protocol 1 in 14- and 21-day-old and adult hearts (45 +/- 5%, 53 +/- 7%, and 58 +/- 5% versus 30 +/- 4%, 29 +/- 3%, and 32 +/- 2% in controls, respectively) but not in 4- and 7-day (neonatal) hearts; neonatal hearts were also not protected in protocol 2. To determine whether this inability of neonatal hearts to precondition was due to insufficient duration of the PC cycle, they were subjected to increased I durations up to 20 minutes before 5-minute R, prolonged I (90 minutes and 60-minute R) (protocol 3); protection was not seen. To determine whether the inability to precondition was due to an excessively prolonged ischemic duration, neonatal hearts were subjected to only 45 minutes of prolonged I (protocol 4); again, PC protection was not evident.Protection by PC develops after 7 days; the inability of neonatal hearts (7 days old) to precondition is not due to insufficient stimulus or extended ischemia.

Restoration of blood flow to the ischemic myocardium prevents continuing cell necrosis, but reperfusion may cause irreversible damage to potentially salvable tissue, possibly through the generation of toxic reactive oxygen species. Intracellular calcium overload, secondary to membrane lipid peroxidation, has been proposed as a general pathogenic mechanism. However, using the photosensitisation of rose bengal to generate singlet oxygen and superoxide radicals, we demonstrate a direct effect of reactive oxygen species on the cardiac sarcoplasmic reticulum calcium-release channel. Exposure of heavy sarcoplasmic reticulum vesicles to reactive oxygen species in vitro resulted in the progressive loss of specific [3H]ryanodine binding and the degradation of high molecular weight proteins identified by polyacrylamide gel electrophoresis. The gating of single channels incorporated into artificial planar phospholipid bilayers was modified during the exposure to reactive oxygen species: an initial increase in open probability being followed by irreversible loss of channel function. Degradation by reactive oxygen species of specific proteins, such as the calcium-release channel, may contribute to in vivo reperfusion injury.