Perinatal changes in myocardial metabolism in lambs

Background—Lactate accounts for a third of myocardial oxygen consumption before and in the first 2 weeks after birth. It is unknown how the remainder of myocardial oxygen is consumed. Glucose is thought to be important before birth, whereas long-chain fatty acids (LC-FA) are the prime substrate for the adult. However, the ability of the myocardium of the newborn to use LC-FA has been doubted. Methods and Results—We measured the myocardial metabolism of glucose and LC-FA with [U-13C]glucose and [1-13C]palmitate in chronically instrumented fetal and newborn lambs. In fetal lambs, myocardial oxidation of glucose was high and that of LC-FA was low. Glucose and LC-FA accounted for 48±4% and 2±2% of myocardial oxygen consumption, respectively. In newborn lambs, oxidation of glucose decreased, whereas oxidation of LC-FA increased. Glucose and LC-FA accounted for 12±3% and 83±19% of myocardial oxygen consumption. To test whether near-term fetal lambs could use LC-FA, we increased the supply of LC-FA with a fat in...