EFFECT OF PARENTERAL AMINO-ACIDS ON LEUCINE AND UREA KINETICS IN PRETERM INFANTS

Objective: To examine the effect of two commonly used parenteral alime ntation amino acid mixtures on whole-body leucine and urea kinetics. M ethods. Ten stable preterm infants were studied during the first 4 wee ks after birth. Six infants received a mixture containing higher branc hed-chain amino acids, lower glycine plus added dicarboxylic acids for mulation (Trophamine), and four received a standard amino acid mixture (Aminosyn). Whole-body protein turnover was measured with (1-C-13)leu cine tracer, and the rate of oxidation of protein was calculated by qu antifying the appearance of carbon 13 from leucine in carbon dioxide a s well as from rates of urea synthesis estimated by using (N-15(2))ure a tracer. Energy consumption and substrate oxidation were quantified b y indirect respiratory calorimetry. Infants were given similar quantit ies of energy (approximate to 61 kcal/kg per day), glucose (approximat e to 10.7 mg/kg per minute) and protein (approximate to 2.1 gm/kg per day). Results: There was no significant difference in the rate of appe arance of leucine in the two groups. However, the fraction of leucine oxidized (p = 0.002) and total rate of oxidation of leucine was higher in the Trophamine group. Thus additional branched-chain amino acids r esulted in an increased contribution of C-1 of leucine to expired CO2. The rate of urea N synthesis was also similar in the two groups (Trop hamine: 2.92 +/- 0.87 mg N/kg per hour; Aminosyn: 2.70 +/- 1.18 mg N/k g per hour). Conclusions: Although the use of Trophamine normalizes th e blood amino acid pattern, it does not appear to improve nitrogen/pro tein kinetics. Furthermore, the additional branched-chain amino acids are disposed of by increased oxidation.