PROTEIN-METABOLISM KINETICS IN NEONATES - EFFECT OF INTRAVENOUS CARBOHYDRATE AND FAT

The aim of this study was to determine the effect of different glucose /fat ratios on protein metabolism kin etics in newborn infants receivi ng total parenteral nutrition (TPN). Eighteen studies were done on 14 infants receiving TPN (weight 3.15 +/- 0.22 kg [mean +/- SEM]; gestati onal age 37.8 +/- 0.9 weeks: postnatal age 14.0 +/- 3.7 days). There w ere two study groups. Group A infants (n = 9) received 10.0 g/kg/d of dextrose and 4.0 g/kg/d of fat; group B infants (n = 9) received 19.0 g/kg/d of dextrose and 0.5 g/kg/d of fat. Caloric intake (86 kcal/kg/d ) and amino-acid intake (2.5 g/kg/d) were the same in the two groups. There was no difference between the groups with regard to weight, gest ational age, and postnatal age. Intravenous diet was constant during t he 3-day study period. Timed urinary nitrogen excretion was determined . On day 3 of the study, each infant received a priming dose of 15 mu mol/kg of [C-13]leucine followed by a 6-hour infusion at 6 mu mol/kg/h . Plasma and breath samples were taken at hourly intervals, and CO2 pr oduction was measured by indirect calorimetry. Plateau levels of plasm a [C-13]-alpha Ketoisocaproic acid (KIC) enrichment and expired (CO2)- C-13 enrichment were determined by gas chromatograph mass spectrometry . Protein metabolism kinetics were Calculated. Results were: nitrogen balance 0.27 +/- 0.01 g/kg/d, total protein flux 10.38 +/- 0.34 g/kg/d , total protein synthesis 9.64 +/- 0.31 g/kg/d, total protein breakdow n 7.86 +/- 0.38 g/kg/d, and total protein oxidation/ excretion 0.92 +/ - 0.04 g/kg/d. There was no significant difference between the two gro ups with regard to any of the components of protein metabolism. This s tudy shows that (1) Infants on TPN have high rates of protein turnover , (2) infants are avid retainers of nitrogen, and (3) carbohydrate and fat have an equivalent effect on protein metabolism. This study has p ositive implications for the use of intravenous fat.