Substrate metabolism in the developing heart

The developing heart undergoes a remarkable metabolic transformation as it adjusts to the higher-oxygen, extrauterine environment. During gestation, glycolysis and lactate oxidation constitute the major sources of adenosine triphosphate (ATP) for the fetal heart. After birth, however, there is a rapid shift from carbohydrate to fatty acid utilization. Despite the transition to primarily aerobic metabolism, the neonatal heart retains an enhanced capacity for anaerobic energy production. This unique metabolic adaptation is important when assessing the immature heart's responses to states of oxygen insufficiency, such as ischemia, hypoxia, and tachycardia. This article reviews the dramatic changes in enzyme activities, mitochondrial morphology and function, and substrate availability that underlie this change in metabolism in the maturing heart.