Perinatal changes in myocardial metabolism in lambs.

Area of Science:

• Cardiology
• Neonatal Physiology
• Metabolic Research

Background:

• Lactate is a significant myocardial oxygen consumer in newborns.
• The primary fuel source for adult heart metabolism, long-chain fatty acids (LC-FA), has been questioned in fetal and newborn hearts.
• Understanding myocardial substrate utilization is crucial for neonatal cardiac health.

Purpose of the Study:

• To investigate the metabolic fate of glucose and LC-FA in fetal and newborn lamb myocardium.
• To determine the contribution of glucose and LC-FA to myocardial oxygen consumption across the perinatal period.
• To assess the fetal heart's capacity to utilize LC-FA as an energy substrate.

Main Methods:

• Utilized stable isotope tracers, [U-(13)C]glucose and [1-(13)C]palmitate, in chronically instrumented fetal and newborn lambs.
• Measured myocardial substrate oxidation rates and their contribution to overall oxygen consumption.
• Administered a fat emulsion to fetal lambs to increase LC-FA supply and assess metabolic response.

Main Results:

• In fetal lambs, glucose was the primary substrate (48%), with minimal LC-FA oxidation (2%).
• In newborn lambs, LC-FA oxidation significantly increased (83%), while glucose oxidation decreased (12%).
• During fat infusion, fetal lamb LC-FA oxidation increased 15-fold, contributing significantly (70%) to myocardial oxygen consumption.

Conclusions:

• Myocardial substrate utilization dramatically shifts from glucose in fetuses to LC-FA in newborns.
• The fetal myocardium possesses the capability to utilize LC-FA as a substantial energy source when available.
• These findings elucidate critical developmental changes in neonatal cardiac energy metabolism.