Palmitate oxidation by isolated working fetal and newborn pig hearts

Palmitate oxidation and the effect of palmitate on glucose and lactate utilization were investigated in isolated, perfused, fetal (0.9 gestation), and neonatal (2 day old) pig hearts. Hearts were perfused under working conditions, developing a mean aortic pressure of 50-55 mmHg, paced at 180 beats/min for 30 min, with Krebs-Henseleit buffer containing 3% albumin, glucose (5 mM), and insulin (100 microU/ml). Palmitate (1 mM) and lactate (5 mM), either individually or in combination, were added to the perfusion buffer. Palmitate oxidation was assessed from 14CO2 production from [U-14C]-palmitate, glucose uptake as 3H2O production from D-[2-3H]-glucose, and lactate metabolism from changes in buffer lactate content. After perfusion, ATP, creatine phosphate, triglycerides, and glycogen were measured. Substantial palmitate oxidation was observed at both ages but was greater in neonatal hearts. Nevertheless, palmitate inhibited lactate utilization and glucose uptake similarly in fetal and neonatal hearts. Lactate also reduced palmitate uptake and oxidation by 40-60% in both fetal and neonatal hearts. During perfusions with palmitate, tissue concentrations of triglycerides increased approximately threefold in fetal hearts and were unaffected by lactate. Thus both palmitate and lactate can act as major energy substrates for the immature heart. Both substrates significantly (P less than 0.01) suppress glucose utilization, and each has suppressive effects on the other's metabolism.