The effects of surgery on the nitrogen metabolism of parenterally fed human neonates.

Nitrogen retention and rates of whole body amino nitrogen flux, protein synthesis, and breakdown were measured in 18 neonates during the 72 h immediately postsurgery. The infants were all intravenously fed with a crystalline amino acid source (Vamin), glucose, and Intralipid The infants were divided into two groups based on amino acid intake: either 2.3 SD 0.4 g or 3.9 SD 0.5 g/kg/day. Nonprotein energy intakes were similar and averaged 81 kcal/kg/day. Group A (n = 11) retained 145 SD 110 mg N/kg/day, whilst group B (n = 7) retained 315 SD 93 mg N/kg/day (p less than 0.001). There were no differences seen in flux, synthesis or breakdown. However, group B had significantly higher net protein synthesis rates (synthesis-breakdown) (p less than 0.01). The improved nitrogen utilization in group B was achieved principally by a reduction in endogenous protein breakdown. There were no differences between the two groups in urinary creatinine or 3-methylhistidine excretion. Since these two parameters reflect skeletal muscle turnover the differences between groups in nitrogen retention and turnover appear to be mediated through visceral protein.