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Insulin Does Not Stimulate Protein Synthesis Acutely in Prepubertal Children with Insulin-Dependent Diabetes Mellitus¹

Department of Pediatrics, Division of Pediatric Endocrinology, Baylor College of Medicine (M.G.V., P.R.B., K.C.C.), Houston, Texas 77030; and the Department of Internal Medicine, Mayo Clinic, Rochester, Minnesota 55905

Address all correspondence and requests for reprints to: Kenneth C. Copeland, M.D., Department of Pediatrics, Baylor College of Medicine, 6621 Fannin, Suite 850, MC: 3–2351, Houston, Texas 77030. E-mail: Copeland{at}msmail.his.tch.tmc.edu

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-[1-¹³C]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 ß-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.

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