Abstract Abstract 193

Dexamethasone (DEX) is an established part of the management of bronchopulmonary dyplasia, but compromises protein metabolism and growth. Protein breakdown is increased in infants at the start but not at the end of a tapering DEX course. We have previously shown that piglets have decreased protein synthesis but not increased breakdown at the end of a tapering DEX course (Ward WE et al, Ped Res1997;236a). It is unclear whether this represents a dose effect or an adaptive mechanism. The aim of this study was to examine the effect of a constant dose of DEX on protein metabolism.

Seven day old male piglets were randomized to a 10 day, constant dose(0.5mg/kg/day) course of DEX (n=8) or placebo (n=7). On the morning of day 915 Nglycine was administered orally (20mg/kg) and urine was collected at timed intervals over 48 hours. Final length and weight were measured on day 11. Total urinary nitrogen was measured by Kjeldahl technique. Enrichment of 15N in urine was assessed by isotope ratio mass spectrometry. The DEX piglets were significantly lighter and shorter than controls. Protein synthesis was significantly reduced in the DEX piglets (12.5 ± 9.8 vs 29.5 ± 13.6g/kg/day p=0.02) and protein breakdown not increased (13.7± 8 vs 22.4 ± 12.6g/kg/day, p=0.16). This is consistent with our previous study, suggesting that timing rather than dose is responsible for the apparent lack of effect on protein breakdown. We speculate that adaptation to the initial effect on breakdown is occurring. (Sponsored by the HSC Foundation, Toronto)