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The Insulin-Like Growth Factor-I Response to Growth Hormone Is Increased in Prepubertal Children with Obesity and Tall Stature

Departments of Pediatrics (N.B.-N., F.G., S.R., R.C.) and Nuclear Medicine (F.B.d.C.), University Hospital, 49033 Angers Cedex 01, France

Address all correspondence and requests for reprints to: Régis Coutant, Department of Pediatrics, University Hospital, 4 rue Larrey, 49033 Angers Cedex 01, France. E-mail: recoutant{at}chu-angers.fr.

Context: Children with obesity [body mass index (BMI) > +2 SD score (SDS)] and children with constitutional tall stature [CTS; height > +2 SDS)] have normal-high serum IGF-I levels, associated with a low and broad range of GH secretion, respectively. This suggests increased sensitivity to GH, whereas children with idiopathic short stature (ISS; height < –2 SDS) are believed to have decreased GH sensitivity.

Objective, Design, and Main Outcome Measure: To compare the responsiveness to GH in 62 prepubertal children (43 females, 19 males) with obesity, CTS, or ISS and 26 controls (15 females, 11 males; height and BMI –2 to +2 SDS), we used an IGF-I generation test and studied the IGF-I concentration 24 h after a single injection of GH (2 mg/m²).

Patients: Twenty patients with obesity, 20 with CTS, 22 with ISS, and 26 controls were studied. The mean age was 8.3 ± 2.9 yr, with no difference in age or gender between groups.

Results: Compared with controls, the mean IGF-I increment was 80% higher in obese children and 36% higher in tall children (P < 0.05 obese or tall vs. control children; P = 0.05 obese vs. tall children). Conversely, the IGF-I increment was similar in short compared with control children, despite a mean baseline IGF-I 62% lower in short children (P < 0.05 vs. controls). In all groups, the IGF-I increment was correlated with the BMI SDS or the fat mass percentage (r = 0.51–0.58, P < 0.05).

Conclusion: Obese children tend to have greater GH responsiveness than tall children, and both have greater GH responsiveness than controls. GH responsiveness was similar in controls and short children, despite a lower baseline IGF-I in short children. Whether the differences in the IGF-I response to GH between these children reflect differences in the respective anabolic (growth promotion) and metabolic (i.e. insulin action modulation) roles of circulating IGF-I is unknown.

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