Extremely Preterm Infants (<28 Weeks) Are Capable of Gluconeogenesis from Glycerol on Their First Day of Life

Extremely preterm infants have been shown capable of producing glucose at a rate comparable to that of term infants, but virtually no data are available on their capacity for lipolysis and gluconeogenesis. To address this issue, we studied the flux of glycerol and its gluconeogenic contribution to hepatic glucose output by determining the endogenous plasma appearance rate of glycerol (glycerol R_a) and its conversion to glucose in 10 newborn infants, 24-27 wk of gestational age. The study was performed during the 1st d of life by tracer dilution technique using[6,6-²H₂]glucose and [2-¹³C]glycerol given as constant rate i.v. infusions. Plasma isotopic enrichments of the tracers were obtained by gas chromatography/mass spectrometry. Endogenous glycerolR_a ranged from 2.4 to 21.6 (median 5.0)μmol·kg^-1·min^-1, of which 31.5% (25.6-64.4%) was converted to glucose. The glucose production rate averaged 17.5 ± 5.4 μmol·kg^-1·min^-1 (3.2 ± 1.0 mg·kg^-1·min^-1), of which 5.0% (1.6-37.6%) was derived from glycerol. The results show that extremely preterm infants, despite limited fat stores, are capable of generating glycerol at a rate within the range reported for term and near term newborns. The infants were also capable of converting part of this glycerol to glucose, providing a contribution to hepatic glucose production comparable to that found in more mature newborns.

Abbreviations: CV, coefficient of variation; GPR, glucose production rate; R_a, appearance rate