Insulin does not stimulate protein synthesis acutely in prepubertal children with insulin-dependent diabetes mellitus

Insulin treatment in adult type I diabetic patients decreases protein loss primarily by inhibiting protein breakdown without stimulating protein synthesis. In young growing rodents, insulin treatment has been reported to stimulate protein synthesis. We examined whether insulin stimulates protein synthesis in normally growing prepubertal children with insulin-dependent diabetes mellitus. Five prepubertal children with insulin-dependent diabetes mellitus (aged 8.6-11.25 yr) were studied in the postabsorptive state on two occasions: once during insulin deprivation (I-; blood glucose, 325 ± 67.8 mg/dL; mean ± SD) and once during insulin administration for 4 h (I+; blood glucose, 96 ± 23.6 mg/dL). Leucine kinetics were measured using a 4-h primed continuous infusion of L-[1-¹⁹C]leucine. Serum insulin concentrations were lower (I- vs. I+. 0.6 ± 0.3 vs. 7.5 ± 4.3 μU/mL; mean ± SD; P = 0.02), whereas serum β-hydroxybutyrate (I- vs. I+, 3.4 ± 0.5 vs. 0.9 ± 0.5 mg/dL; P < 0.001) and free fatty acid concentrations (I- vs. I +, 2.9 ± 0.4 vs. 0.9 ± 0.4 mEq/L; P < 0.001) were higher in the insulin-deprived state than during insulin administration Leucine Ra, an index of protein breakdown (I - vs. I +, 200.5 ± 23.4 vs. 167 ± 17 μmol/kg·h; P = 0.008), and leucine oxidation (I- vs. I+, 56.5 ± 20.7 vs. 29.6 ± 9.3 μmol/kg·h;P = 0.03) were reduced by insulin treatment. Nonoxidative leucine disposal, an index of protein synthesis, was not affected by insulin treatment (I- vs. I+ 144 ± 20.8 vs. 137.5 ± 13.5 μmol/kg·h; P = 0.4). We conclude that the acute decline in net protein loss during insulin treatment in growing prepubertal children, like that in adults, is due primarily to an inhibition of protein breakdown without stimulation of protein synthesis.