15N Tracer Techniques for the Differential Diagnosis of Dwarfism and Prediction of Growth Hormone Action in Children

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Abstract
[15N]Glycine in a single oral dose was used to study nitrogen turnover in 18 short children, aged 3-14 yr. On the basis of their serum GH responses to insulin-induced hypoglycemia, the patients were divided into 3 groups: complete GH deficiency (GHD; n = 5); partial GH deficiency (pGHD; n = 6), and children with constitutional growth delay and familial short stature (CGD/FSS; n = 7). The mean 48-h renal excretion of 15N by patients with GHD was 66.09 .+-. 14.12% (.+-.SD) of the tracer dose. This decreased to 27.64 .+-. 5.33% after two injections of 10 IU/m2 GH (P < 0.001). 15N excretion by patients with pGHD was 47.19 .+-. 13.42%, and it decreased after GH injection to 22.69 .+-. 4.58% (P < 0.005). Patients with CGD/FSS had 15N excretion of 37.27 .+-. 5.68%, and it did not change in response to GH. The mean protein synthesis rate in GHD patients was extremely low, and it increased after GH injection from 0.99 .+-. 0.46 to 3.53 .+-. 0.43 g/kg .cntdot. day. In pGHD patients the protein synthesis rate increased from 2.62 .+-. 0.84 to 4.50 .+-. 1.09 g/kg .cntdot. day. The CGD/FSS patients had no change in protein synthesis rate after GH. Our results suggest that studies of the metabolism of [15N]glycine might be of value in predicting responsiveness to GH therapy.