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. W e studied five healthy control children and five children with cystic fibro sis (CF). After an overnight fast, the children ingested, hourly, a formula diet for 11 h. 5,5,5-[H-2(3)]Leucine was added to the feedings during the last 6 h, and an i.v. infusion of 1-[C-13]leucine was administered during t he last 2 h of the formula feeding, The mean rare of splanchnic uptake of l eucine was similar in the CF and control group, 23.8 +/- 24.0 and 21.5 +/- 21.2 mu mol.kg(-1).h(-1), respectively. Fractional splanchnic uptake of leu cine was not significantly different in the patients with CF (0.16 +/- 0.11 2 mean +/- SD) compared with the control children (0.244 +/- 0.256(-1)). Th e rate of whole body protein breakdown was not significantly different betw een the groups (CF versus control) with (159 +/- 18 versus 135 +/- 28 mu mo l.kg(-1).h(-1)) or without (135 +/- 14 versus 114 +/- 20 mu mol.kg(-1).h(-1 )) correction for splanchnic leucine uptake. However, for the 10 cases comb ined, protein breakdown corrected for splanchnic leucine uptake (147 +/- 26 mu mol.kg(-1).h(-1)) was 18% greater than uncorrected protein breakdown (1 24 +/- 20 mu mol.kg(-1).h(-1)) (p = 0.009). The data suggest that companion studies of splanchnic uptake might enhance the interpretation of leucine k inetics in the fed state.