EFFECTS OF SPLANCHNIC UPTAKE (SU) OF LEUCINE (LEU) ON THE MEASUREMENT OF WHOLE BODY PROTEIN BREAKDOWN (B) IN HEALTHY CHILDREN (HC) AND IN CHILDREN WITH CYSTIC FIBROSIS (CF). † 710

HYPOTHESIS: SU of LEU is abnormal in CF, affecting estimates of B. METHODS: Prepubertal children with CF (N=5;6.6-11.1 yr) and 5 HC(8.7-9.9 yr) were studied. After an overnight fast, a formula was ingested, q 1 hr, for 11 hr. [5,5,5-²H₃] -LEU (²H-Leu) was added to the diet for the last 6 hr, and [1-¹³C] -Leu was infused intravenously during the last 2 hr. Plateau isotopic enrichment of plasma 2-ketoisocaproic acid was assessed. RESULTS/CONCLUSION: SU of ²H-Leu was not significantly different in CF vs. HC (11.8±7.0% vs. 24.4±25.6%). Estimates of B (μmol/kg/hr) were not different between CF vs. HC with(152.6±14.4 vs. 135.2±28.1) or without (138.5±13.0 vs. 113.7±20.1) correction for SU (respective 13% and 22% increases in B in CF (P>0.05). However, the large inter-individual variation suggests that companion studies of SU might enhance the interpretation of leucine kinetics in the fed state. (Support: CF Found.; NIH Grant No. M01-RR00034; Child. Hosp. Res. Found.)