We used the radioimmunoassay (RIA) method to determine somatomedin-C (SmC) basal values in 59 diabetic children and adolescents (20 prepubertal and 39 pubertal subjects; age range 2.75–20.16 yr; duration of diabetes 0.08–15.83 yr) and in 274 control subjects. In comparing diabetic subjects with controls, we considered only those 50 diabetic subjects who were age matched with the controls, i.e., those not over 16 yr chronological age. SmC basal levels in pubertal diabetic patients were no different from those of pubertal age-matched control children, whereas in prepubertal diabetic patients SmC was significantly lower than in the respective control children (P < .001). No correlation was found between the z score for SmC (i.e., the number of standard deviations each SmC level is from the age- and sex-normalized mean) and duration of disease, velocity standard deviation score, severity of fluoroangiographic retinal changes, basal C-peptide values and HbA, levels. No differences were encountered in mean SmC and SmC z-score values in the separate groups of poorly, fairly, and well-controlled diabetic children, in the groups with and without residual pancreatic activity, and in the group with and without retinal changes. In 16 of the pubertal diabetics and in 15 pubertal controls, serum glucose, growth hormone (GH), and SmC concentrations were determined during the night. The integrated nocturnal secretion of SmC was no different in diabetics than in controls, whereas the integrated nocturnal secretion of GH was significantly (P < .025) higher in diabetics than in controls. These data suggest a partial block in somatomedin production, which would be compensated by a hypersecretion of GH through a negative-feedback relationship. On the other hand, it may be that GH hypersecretion is primary and that the normal or low SmC secretion is a response to low-efficiency GH.

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