GLUCOSE-PRODUCTION AND GLUCONEOGENESIS ARE NEGATIVELY RELATED TO BODY-WEIGHT IN MECHANICALLY VENTILATED, VERY-LOW-BIRTH-WEIGHT NEONATES

The regulation of gluconeogenesis by low birth weight infants remains poorly delineated. To investigate this, 15 5-d-old infants (26-31-wk g estational age, 795-1485-9 body weight), were infused i.v. for 4 h wit h uniformly labeled [U-C-13]glucose (5 mg/kg/min) as the sole source o f glucose. Intralipid (3 mg/kg/ min) was provided, but no amino acids were given. Blood samples were taken immediately before and after 4 h of tracer infusion, The isotopic enrichments of plasma glucose and ala nine were measured by selected ion monitoring gas chromatography mass spectrometry. Glucose production rates were calculated from the isotop ic dilution of plasma [U-C-13]glucose and the glucose infusion rate. G luconeogenesis was estimated from the relative isotopic enrichments of [M + 3]- and [M + 6]-glucose, using the isotopic enrichment of plasma [U-C-13]alanine, to define the isotopic dilution of the 3-carbon pool , and previously published equations to calculate the isotopic dilutio n of hepatic oxaloacetate. Glucose production (15 +/- 9 mu mol/kg/min) was negatively related to body weight (r = -0.67; p < 0.05) and the r atio of the isotopic enrichments of [C-13(3)]alanine:[C-13(6)]glucose (0.27 +/- 0.07) was positively related to body weight (r = 0.74; p < 0 .025). Both relationships were exponential. Gluconeogenesis (via pyruv ate) accounted for 72 +/- 28% of glucose production, and gluconeogenes is per unit body weight was negatively and exponentially (r = -0.82; p < 0.005) related to body weight. These results demonstrate that neona tes whose birth weights are less than 1200 g have a particularly high glucose production rate secondary to enhanced gluconeogenesis. We spec ulate that these results reflect a high weight-specific glucose demand that is met by up-regulation of gluconeogenesis.