Perinatal changes in myocardial metabolism in lambs

Background-Lactate accounts for a third of myocardial oxygen consumption be fore 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 ann Results-We measured the myocardial metabolism of glucose and LC -FA with [U-C-13]glucose and [1-C-13]palmitate in chronically instrumented fetal and newborn lambs. In fetal lambs, myocardial oxidation of glucose wa s high and that of LC-FA was low. Glucose and LC-FA accounted for 48+/-4% a nd 2+/-2% of myocardial oxygen consumption, respectively. In newborn lambs, oxidation of glucose decreased, whereas oxidation of LC-FA increased. Gluc ose and LC-FA accounted for 12+/-3% and 83+/-19% of myocardial oxygen consu mption. 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 infusio n, the oxidation of LC-FA increased 15-fold. Although the oxidation of LC-F A was still lower than in newborn lambs, the contribution to myocardial oxy gen consumption (70+/-13%) was the same as in newborn lambs. Conclusions-These data show that glucose and lactate account for the majori ty of myocardial oxygen consumption in fetal lambs, whereas in newborn lamb s, LC-FA and lactate account for the majority of myocardial oxygen consumpt ion. Moreover, we showed that the fetal myocardium can use LC-FA as an ener gy substrate.