Effect of Intravenous Amino Acids on Protein Metabolism of Preterm Infants during the First Three Days of Life

Abstract

ABSTRACT: Twenty-three preterm infants with respiratory distress syndrome (mean birth weight 1.07 kg, SD 0.24 kg) were randomly assigned to receive glucose alone or glucose with amino acids (1.5 g·kg⁻¹·d⁻¹) i.v. beginning on the 1st d of life. Blood ammonia and serum urea, CO₂ content, sodium, potassium, chloride, and ionized calcium concentrations were normal and did not differ between treatment groups. Nitrogen balance was significantly greater in the group that received amino acids [88 (SD 54) versus −135 (SD 45) mg·kg⁻¹ d⁻¹]. In 12 infants (seven, glucose-only; five, glucose and amino acids), leucine kinetic studies were also performed on the 3rd d of life. These 12 infants received a 4-h primed constant infusion of L-[1-¹³C] leucine. Blood and breath were collected and analyzed for [1-¹³C]ketoisocaproate and ¹³CO₂, respectively. Leucine turnover and oxidation were calculated. Both leucine turnover and oxidation were significantly higher in the group receiving amino acids than in the glucose-only group [241 (SD 38) versus 164 (SD 25) μmol·kg⁻¹·h⁻¹ and 71 (SD 22) versus 40 (SD 17) μmol·kg⁻¹·h⁻¹, respectively]. In addition, the calculated rate of protein synthesis was higher in the group receiving amino acids [6.9 (SD 1.1) versus 5.0 (SD 1.2) g·kg⁻¹·d⁻¹]. These data indicate that the i.v. administration of amino acids (1.5 g·kg⁻¹·d⁻¹) to ill preterm infants beginning on the 1st d of life improves whole-body protein balance as a result of increased protein synthesis.

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