Somatomedin Levels in the Diagnosis and Therapy of Growth Hormone Deficiency

Summary

Serum somatomedin-C (SM-C) and somatomedin (SM) concentrations were measured by, respectively, radioimmuno (SM-C RIA) and radioreceptor assays (SM RRA) in 3 groups of children with short stature. The patient population was different from previously reported series in that it was urban Brazilian, low income, and significantly older. Group A consisted of 6 male and 3 female children, aged 7.7-16.0 years, whose average peak plasma immunoreactive growth hormone (GH) was above 10 ng/ml. Group B contained 8 male and 5 female untreated GH-deficient patients, ranging in age from 9.5 to 21.0 years. In Group C there were 4 male and 1 female GH-deficient subjects treated with I.M. injections of GH (0.1 U/kg) from 1 month to 7 years.

The mean±SE basal RIA SM-C (ng/ml) concentrations were significantly lower in groups B (34.2±8.8) and C (43.8±13.7) than A (214.3±42.7): A × B, P < 0.001 and A × C, P < 0.02. Likewise the mean±SE basal RRA SM (ng/ml) concentrations were significantly lower in groups B (78.9±17.6) and C (90.8±19.3) than group A (316.3±43.0): A × B, P < 0.001 and A × C, P < 0.002. A significant linear correlation was observed between RIA and RRA in group B (r=0.84; P < 0.001) and C (r=0.96; P < 0.01), but not for A (r=0.61; P > 0.05).

Both the serum SM-C RIA and SM RRA were equally useful in differentiating children with short stature and normal GH dynamics from untreated and treated GH-deficient children. Part of the reason for this finding could be the significantly older age of our children than previously reported. After GH treatment of GH-deficient children. SM-C and SM values failed to return to normal and did not correlate with the increase in height velocity. This is consistent with GH-induced stimulation of local SM production being the important parameter as opposed to the serum SM-C level.

Key-Words

Somatomedin - Growth Deficiency - hGH Treatment