Substrate utilization during the first weeks of life

Abstract

It is assumed that substrate utilization changes markedly around birth, from mainly glucose utilization before, to glucose/fat utilization after birth. We studied substrate oxidation and turnover in preterm infants on the first day and during the first weeks of life. We found that only part of the glucose that is infused on the first day of life is oxidized, while glucose is also converted into fat at the same time. Almost half of the energy expenditure is provided by fat oxidation on day 7 and 28 of life. Fat oxidation is dependent on the type of fat oxidized; the rate of oxidation of medium chain triglycerides (MCT) is higher than that of long chain fatty acids. MCT can replace glucose as an energy source. Proteins contribute only to a small extent (approximately 7%) to the energy expenditure at all ages.

Mitochondrial Energy Metabolism in Very Premature Neonates

“…Almost half of the energy expenditure in neonates after birth is provided by fat oxidation. The rate of oxidation of medium-chain triglycerides is higher than that of long-chain fatty acids [16]. A significant negative correlation was found between erythrocyte pyruvate kinase activity and gestational age.…”

“…The parameters of acidobasic balance are insufficient to confirm metabolic disturbances and hyperlactacidemia in children, because the lactate level in blood neither correlates with pH nor with base excess values [24]. It is known that only a part of the glucose infused into premature neonates during the first days of life is oxidized [16]. The higher dose of insulin necessary to correct hyperglycemia in premature neonates with a low PDH activity may therefore increase the lactate level and further worsen the metabolic acidosis.…”

Endogenous Surfactant Turnover in Preterm Infants Measured with Stable Isotopes

“…We measured endogenous PC palmitate synthesis from glucose only. We have recently demonstrated that lipogenesis from glucose occurs in preterm infants fed solely glucose intravenously on the first day of life (29). Therefore, with our approach carbon-13 incorporation into surfactant PC occurs via lipogenesis in type II cells directly or via lipogenesis in the liver and subsequent uptake of labeled palmitic acid by type II cells.…”

The Role of Parenteral Lipids in Supporting Gluconeogenesis in Very Premature Infants

“…On a per gram basis, Intralipid is a very important source of energy, providing nearly three times that of glucose. Thus, providing glucose at a rate equivalent to the basal glucose turnover rate of these infants (6 -8 mg/kg/min or 33-44 mol/ kg/min) in addition to currently recommended rates of lipid (~3 g/kg/d on d 3-4 of life) and amino acid substrate (important for protein synthesis) (~3 g/kg/d) may be a potential strategy to reduce the risk of hyperglycemia without increasing the risk of either energy insufficiency (27,28) or hypoglycemia.…”