Possible role of mitochondrial K-ATP channel and nitric oxide in protection of the neonatal rat heart.

Cardioprotective effect of ischemic preconditioning (IPC) and ischemic postconditioning (IPoC) in adult hearts is mediated by mitochondrial-K-ATP channels and nitric oxide (NO). During early developmental period, rat hearts exhibit higher resistance to ischemia-reperfusion (I/R) injury and their resistance cannot be further increased by IPC or IPoC. Therefore, we have speculated, whether mechanisms responsible for high resistance of neonatal heart may be similar to those of IPC and IPoC. To test this hypothesis, rat hearts isolated on days 1, 4, 7, and 10 of postnatal life were perfused according to Langendorff. Developed force (DF) of contraction was measured. Hearts were exposed to 40 min of global ischemia followed by reperfusion up to the maximum recovery of DF. IPoC was induced by 5 cycles of 10-s ischemia. Mito-K-ATP blocker (5-HD) was administered 5 min before ischemia and during first 20 min of reperfusion. Another group of hearts was isolated for biochemical analysis of 3-nitrotyrosine, and serum samples were taken to measure nitrate levels. Tolerance to ischemia did not change from day 1 to day 4 but decreased on days 7 and 10. 5-HD had no effect either on neonatal resistance to I/R injury or on cardioprotective effect of IPoC on day 10. Significant difference was found in serum nitrate levels between days 1 and 10 but not in tissue 3-nitrotyrosine content. It can be concluded that while there appears to be significant difference of NO production, mito-K-ATP and ROS probably do not play role in the high neonatal resistance to I/R injury.

Nitric oxide is involved in the cardioprotection of neonatal rat hearts, but not in neonatal ischemic postconditioning.

The cardioprotective effect of ischemic preconditioning (IPC) and ischemic postconditioning (IPoC) in adult hearts is mediated by nitric oxide (NO). During the early developmental period, rat hearts exhibit higher resistance to ischemia-reperfusion (I/R) injury, contain higher levels of serum nitrates, and their resistance cannot be further increased by IPC or IPoC. NOS blocker (L-NAME) lowers their high resistance. Wistar rat hearts (postnatal Days 1 and 10) were perfused according to Langendorff and exposed to 40 min of global ischemia followed by reperfusion with or without IPoC. NO and reactive oxygen species donors (DEA-NONO, SIN-1) and L-NAME were administered. Tolerance to ischemia decreased between Days 1 and 10. DEA-NONO (low concentrations) significantly increased tolerance to I/R injury on both Days 1 and 10. SIN-1 increased tolerance to I/R injury on Day 10, but not on Day 1. L-NAME significantly reduced resistance to I/R injury on Day 1, but actually increased resistance to I/R injury on Day 10. Cardioprotection by IPoC on Day 10 was not affected by either NO donors or L-NAME. It can be concluded that resistance of the neonatal heart to I/R injury is NO dependent, but unlike in adult hearts, cardioprotective interventions, such as IPoC, are most likely NO independent.

Neonatal cardiac mitochondria and ischemia/reperfusion injury.

Postnatal maturation of the heart is characterized by decreasing tolerance to ischemia/reperfusion (I/R) injury associated with significant changes in mitochondrial function. The aim of this study is to test the hypothesis that the role of the mitochondrial membrane permeability transition pore (MPTP) in the I/R injury differs in the neonatal and in the adult heart. For this purpose, the effect of blockade of MPTP on the degree of I/R injury and the sensitivity of MPTP to swelling-inducing agents was compared in hearts from neonatal (7 days old) and adult (90 days old) Wistar rats. It was found that the release of NAD(+) from the perfused heart induced by I/R can be prevented by sanglifehrin A (SfA) only in the adult myocardium; SfA had no protective effect in the neonatal heart. Furthermore, the extent of Ca-induced swelling of mitochondria from neonatal rats was significantly lower than that from the adult animals; mitochondria from neonatal rats were more resistant at higher concentrations of calcium. In addition, not only the extent but also the rate of calcium-induced swelling was about twice higher in adult than in neonatal mitochondria. The results support the idea that lower sensitivity of the neonatal MPTP to opening may be involved in the mechanism of the higher tolerance of the neonatal heart to I/R injury.