Glycerol carbon contributes to hepatic glucose production during the first eight hours in healthy term infants.

The newborn infant must mobilize endogenous substrate stores to meet the requirements of glucose-dependent organs. High concentrations of free fatty acids and glycerol, and a rapid decrease in the respiratory quotient, indicate that lipids are an important fuel soon after birth. The purpose of the present study was to determine the onset of lipolysis and gluconeogenesis from glycerol in healthy, term, unfed infants. Eight infants were studied from a postnatal age of 3.5 +/- 0.5 h to 7.4 +/- 0.2 h using [6,6-2H2] glucose and [2-13C]glycerol analysed by gas chromatography/mass spectrometry. Plasma concentrations of glucose, glycerol and insulin averaged 2.9 +/- 0.4 mM, 369 +/- 89 microM and 9.4 +/- 9.4 +/- 3.7 microU.ml-1, respectively. The hepatic glucose production rate averaged 25.0 +/- 3.5 mumol.kg-1 min-1 (4.5 +/- 0.6 mg.kg-1.min-1) and the endogenous plasma appearance rate of glycerol 8.7 +/- 1.2 mumol.kg-1.min. On average, 57.9 +/- 8.4% of the glycerol was converted to glucose, representing 11.1 +/- 2.3% of hepatic glucose output. Thus, lipolysis and gluconeogenesis from glycerol are established within the first 8 h of life in term infants.