KINETICS OF PLASMA ARGININE AND LEUCINE IN PEDIATRIC BURN PATIENTS

The dynamic status of whole-body arginine and leucine was investigated in eight severely burned (mean 55% of body surface area) pediatric pa tients (mean age 5.3 y) at a mean of 16 d after their initial injury. Plasma amino acid kinetics were estimated by using primed constant int ravenous infusions of L-[C-13-guanidino]arginine and L-[1-C-13]leucine given for 4 h. Each patient was studied twice within 2 d. The patient s were studied either in a ''basal'' state, which involved removal of amino acids from the the total parenteral nutrition (TPN) solution for 8 h before the tracer study, or while receiving complete TPN. Nitroge n intake was 0.58 +/- 0.08 g . kg(-1). d(-1) with nonprotein energy in take equivalent to 197 +/- 29 kJ . kg(-1). d(-1). Plasma leucine and a rginine fluxes (mu mol . kg(-1). h(-1)) were 208 +/- 35 and 108 +/- 18 for basal and 290 +/- 38 and 195 +/- 22 for TPN periods, respectively . Leucine oxidation was 42 +/- 7 and 59 +/- 9 mu mol . kg(-1). h(-1) f or basal and TPN periods, respectively, indicating a higher rate of le ucine loss in the absence of a leucine intake than that expected for h ealthy individuals. The arginine kinetic data implied little net de no vo arginine synthesis and further suggested increased rates of arginin e degradation from burn injury. The expected rate of urea excretion, b ased on the basal rate of leucine oxidation, agreed closely with the m easured output of urinary urea. These findings suggest that arginine i s a conditionally indispensable amino acid for maintaining body protei n homeostasis and nutrition in severely burned pediatric patients. The metabolic response of these children appears to be quantitatively sim ilar to that for severely burned adult patients.