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-(13)C]glucose and [1-(13)C]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 infusion. In fetal lambs during fat infusion, the oxidation of LC-FA increased 15-fold. Although the oxidation of LC-FA was still lower than in newborn lambs, the contribution to myocardial oxygen consumption (70+/-13%) was the same as in newborn lambs. CONCLUSIONS These data show that glucose and lactate account for the majority of myocardial oxygen consumption in fetal lambs, whereas in newborn lambs, LC-FA and lactate account for the majority of myocardial oxygen consumption. Moreover, we showed that the fetal myocardium can use LC-FA as an energy substrate.