Long-term oxandrolone treatment increases muscle protein net deposition via improving amino acid utilization in pediatric patients 6 months after burn injury

Background. We recently showed that mechanisms of protein turnover in skeletal muscle are unresponsive to amino acid (AA) infusion in severely burned pediatric patients at 6 months postinjury. In the current study, we evaluated whether oxandrolone treatment affects mechanisms of protein turnover in skeletal muscle and whole-body protein breakdown in pediatric burn patients 6 months postinjury. Methods. At the time of admission, patients were randomized to control or oxandrolone treatments. The treatment regimens were continued until 6 months postinjury, at which time patients (n = 26) underwent study with a stable isotope tracer infusion to measure muscle and whole-body protein turnover Results. Protein kinetics in leg muscle were expressed in nmol/min per 100 mL leg volume (mean +/-SE). During AA infusion, rates of protein synthesis in leg muscle were increased (P < .05) in both groups (basal vs AA: control, 51 +/- 8 vs 86 +/- 21; oxandrolone, 56 +/- 7 vs 96 +/- 12). In the control group, there was also a simultaneous increase in breakdown (basal vs AA: 65 +/- 10 vs 89 +/- 25), which resulted in no change in the net balance of leg muscle protein (basal vs AA: -15 +/- 4 vs -2 +/- 10). In the oxandrolone group, protein, breakdown did not change (basal vs AA: 80 +/- 12 vs 77 +/- 9), leading to increased net balance (basal vs AA: -24 +/- 7 vs 19 +/- 7;P < .05). Protein breakdown at the whole-body level was not different between the groups. Conclusion. Long-term oxandrolone treatment increased net deposition of leg muscle protein, during AA infusion by attenuating protein breakdown, but did not affect whole-body protein breakdown. (Surgery 2011; 149: 645-53.)