['Although surgical ligation effectively reverses the cardiopulmonary failure associated with patent ductus arteriosus (PDA), previous findings have suggested that such surgery itself elicits a catabolic response in premature neonates. Therefore, the authors sought to quantitatively assess whether PDA ligation under fentanyl anesthesia aggravated or improved the protein metabolism of premature neonates.', 'Seven ventilated, premature neonates (birth weight 815 +/- 69 g) underwent PDA ligation with standardized fentanyl anesthesia (15 microg/kg) on day-of-life 8.4 +/- 1.2 and were studied immediately pre- and 16 to 24 hours postoperatively while receiving continuous total parenteral nutrition (TPN). Whole-body protein kinetics were calculated using intravenous 1-[13C]leucine, and skeletal muscle protein breakdown was measured from the urinary 3-methylhistidine to creatinine ratio (MH:Cr).', 'Whole-body protein breakdown (10.9 +/- 1.2 v8.9 +/- 0.8 g/kg/d, P < .05), turnover (17.4 +/- 1.2 v 15.4 +/- 0.8 g/kg/d, P< .05), and MH:Cr (1.95 +/- 0.20 v 1.71 +/- 0.16 micromol:mg, P< .05) decreased significantly after operation. This resulted in a 60% improvement in protein balance (1.6 +/- 0.8 v 2.6 +/- 0.6 g/kg/d, P = 0.08) postoperatively.'] Does ligation of a patent ductus arteriosus under fentanyl anesthesia improve protein metabolism in premature neonates?