EFFECTS OF FEEDING ON PROTEIN-TURNOVER IN HEALTHY-CHILDREN AND IN CHILDREN WITH CYSTIC-FIBROSIS

We hypothesized that there is less suppression of whole-body protein b reakdown with feeding in patients with cystic fibrosis (CF) who exhibi t decreased insulin secretion after a single meal. Using [1-C-13]leuci ne, we measured rates of nonoxidative leucine disappearance (whole-bod y protein synthesis) and protein breakdown in nine CF patients (6-11 y of age) and five healthy control subjects (8-10 y of age) during feed ing and fasting. In the CF patients, synthesis and breakdown ((x) over bar +/- SD) were 172 +/- 61 and 157 +/- 67 mu mol . kg(-1). h(-1) dur ing feeding and 140 +/- 24 and 178 +/- 26 mu mol . kg(-1). h(-1) durin g fasting. The respective control values were 129 +/- 27 and 114 +/- 2 0 mu mol . kg(-1). h(-1) during feeding and 136 +/- 13 and 173 +/- 18 mu mol . kg(-1). h(-1) during fasting. Leucine balance was nearly iden tical in the two groups. By analysis of variance, there was a signific ant effect of feeding on protein breakdown but no difference between t he groups. However, when each group was analyzed separately, feeding r esulted in a 34% decrease in breakdown in the control subjects (P = 0. 001) and a 23% increase in synthesis in the CF group (P = 0.058). Plas ma insulin concentrations did not differ in the two groups. Thus, feed ing may affect protein turnover differently in children with CF than i n control children independently of plasma insulin concentration.