Effect of hypoxia on myocardial high-energy phosphates in the neonatal mammalian heart.

The effect of hypoxia on myocardial high-energy phosphate content in the newborn, 2-wk-old, and adult rabbit was determined and compared with mechanical function. Studies were done on the ventricular septum arterially perfused with Krebs-Henseleit bicarbonate buffer solution equilibrated with 95% O2 and 5% CO2 (control) or 95% N2 and 5% CO2 (hypoxia) at 60 beats/min and 27 degrees C. In the adult, ATP concentration decreased to 68%, 56%, and 39% of control after 2, 30, and 60 min of hypoxia, respectively. After 30 min of hypoxia, ATP concentration was not different from control in the newborn but decreased to 82% of control in the 2-wk-old. After 2 min of hypoxia, creatine phosphate concentration decreased to 55% and 10% of control in the newborn and adult rabbit, respectively. Lactate production increased significantly during hypoxia and was greater in the newborn than in the adult. The data indicate that the newborn rabbit is capable of maintaining glycolysis and normal levels of myocardial ATP during hypoxia, which ensures normal myocardial mechanical function for longer periods than in the adult.