Leucine Kinetics during Simultaneously Administered Insulin and Dexamethasone in Preterm Infants with Severe Lung Disease

The objective of this study was to determine whether insulin administration would prevent the well-documented catabolic effect of dexamethasone given to preterm infants with chronic lung disease. We studied leucine metabolism in 11 very-low-birth-weight infants before dexamethasone treatment and on d 2, 4, and 7 thereafter. During the first 4 d of dexamethasone, insulin was administered i.v. at a dose of 0.5 ( n = 7) or 1.0 ( n = 5) IU/kg/d. Leucine turnover was not significantly different between d 0 (337 ± 41.3 μmol leucine/kg/h), d 2 (288 ± 27.2 μmol leucine/kg/h), d 4 (302 ± 22.1 μmol leucine/kg/h), and d 7 (321 ± 21.2 μmol leucine/kg/h), and neither was leucine breakdown (272 ± 21.9 μmol leucine/kg/h on d 0, 225 ± 21.5 μmol leucine/kg/h on d 2, 231 ± 21 μmol leucine/kg/h on d 4, and 242 ± 17.6 μmol leucine/kg/h on d 7). Weight gain rates were significantly lower during the first week of dexamethasone treatment compared with the week before treatment or the second and third week. We conclude that during insulin and corticosteroid administration in very-low-birth-weight infants, no changes were observed in leucine kinetics in contrast to previous studies. The decrease in weight gain was not reversed.