Relations among arginine, citrulline, ornithine, and leucine kinetics in adult burn patients.

Plasma fluxes of arginine, citrulline, and leucine, and the rate of conversion of labeled citrulline to arginine (Qcit-->arg) were determined in nine severely burned patients (mean: 56% body surface burn area, mean 10 d postinjury) while they received total parenteral nutrition (TPN) including an L-amino acid mixture that supplied a generous amount of nitrogen (mean: 0.39 +/- 0.02 g.kg-1.d-1). Plasma fluxes were also studied in these patients during a basal state (low-dose intravenous glucose) by using a primed, 4-h constant intravenous tracer-infusion protocol. Stable-nuclide labeled tracers were L-[15N-15N-guanidino,5,5,2H2]arginine; L-[13C-ureido]citrulline; L-[1-13C]leucine; and NaH13CO3 (prime only), with blood and expired air samples drawn at intervals to determine isotopic abundance of arginine, citrulline, ornithine, and alpha-ketoisocaproate (KIC; for leucine) in plasma and 13CO2 in breath. Leucine kinetics (flux and disappearance into protein synthesis) confirmed the anticipated higher protein turnover in these burn patients compared with healthy control subjects. The plasma arginine fluxes were correspondingly higher in burn patients than in healthy control subjects. However, the citrulline flux and rate of conversion of citrulline to arginine were not higher than values obtained in our laboratories in healthy adult subjects. We hypothesize that the higher rates of arginine loss from the body after burn injury would need to be balanced by an appropriate exogenous intake of preformed arginine to maintain protein homeostasis and promote recovery from this catabolic condition.