Splanchnic Uptake Of Leucine in Healthy Children and in Children with Cystic Fibrosis

Interpretation of tracer studies of amino acid kinetics in the fed state is dependent on knowledge of splanchnic uptake of diet-derived amino acids. We studied five healthy control children and five children with cystic fibrosis (CF). After an overnight fast, the children ingested, hourly, a formula diet for 11 h. 5,5,5-[2H3]Leucine was added to the feedings during the last 6 h, and an i.v. infusion of 1-[13C]leucine was administered during the last 2 h of the formula feeding. The mean rate of splanchnic uptake of leucine was similar in the CF and control group, 23.8 ± 24.0 and 21.5 ± 21.2 µmol·kg-1·h-1, respectively. Fractional splanchnic uptake of leucine was not significantly different in the patients with CF (0.16 ± 0.112 mean ± SD) compared with the control children (0.244 ± 0.256-1). The rate of whole body protein breakdown was not significantly different between the groups (CF versus control) with (159 ± 18 versus 135 ± 28 µmol·kg-1·h-1) or without (135 ± 14 versus 114 ± 20 µmol·kg-1·h-1) correction for splanchnic leucine uptake. However, for the 10 cases combined, protein breakdown corrected for splanchnic leucine uptake (147 ± 26 µmol·kg-1·h-1) was 18% greater than uncorrected protein breakdown (124 ± 20 µmol·kg-1·h-1) (p = 0.009). The data suggest that companion studies of splanchnic uptake might enhance the interpretation of leucine kinetics in the fed state.