Effect of ischemia on mechanical function and high-energy phosphates in rabbit myocardium

This study was designed to evaluate the effect of ischemia and reperfusion on myocardial mechanical function and high-energy phosphates in the neonate. All studies were performed utilizing the isolated arterially perfused septal preparation of newborn and adult rabbit hearts that were maintained at 27, 33, or 37 degrees C and paced at 90 beats/min. After mechanical function had been stabilized, 60 min of global ischemia was induced and was followed by 60 min of reperfusion. The muscle was kept in a humidified, warm, oxygen-poor atmosphere. During ischemia, developed tension (DT) and maximal rate of tension development (+dT/dtmax) declined at the same rate in the newborn and the adult, and the values at the end of ischemia were not significantly different from 0. The resting tension (RT) increased significantly in the two age groups during ischemia, but the increase in the newborn was significantly less than that in the adult. After 60 min of reperfusion, the recovery of +dT/dtmax in the newborn was significantly greater than that in the adult at each temperature. Tissue ATP content in the newborn was significantly greater than that in the adult, both at the end of ischemia and after reperfusion. Importantly, a significant correlation (r = 0.90) between the recovery of +dT/dtmax and tissue ATP content was found. These data indicate that 1) the newborn myocardium is more resistant to ischemia than the adult myocardium and 2) this resistance might be explained by less depletion of myocardial ATP levels during ischemia.