PERINATAL CHANGES IN MYOCARDIAL SUPPLY AND FLUX OF FATTY-ACIDS, CARBOHYDRATES, AND KETONE-BODIES IN LAMBS

No information is available on perinatal changes in myocardial metabol ism in vivo. We measured myocardial supply and flux of fatty acids, ca rbohydrates, and ketone bodies in chronically instrumented fetal, newb orn (1-4 days), and juvenile (7 wk) lambs, by measuring aorta-coronary sinus concentration differences and blood flow. In the fetal lambs, m yocardial supply and flux of fatty acids were zero. In the newborn lam bs, the supply of fatty acids increased tenfold, but there was no flux of fatty acids. Carbohydrates were the major energy source in fetal a nd newborn lambs, accounting for 89 and 69% of myocardial oxygen consu mption, respectively In the juvenile lambs, the flux of fatty acids wa s increased threefold. The supply and flux of carbohydrates were decre ased (by 31 and 82%, respectively). The supply and flux of ketone bodi es gradually increased with age. We show that the myocardium of the la mb in vivo does not switch immediately after birth from carbohydrates to fatty acids. The mechanisms involved in the development of myocardi al fatty acid oxidation remain to be elucidated.