Abstract
Somatomedin-C/insulin-like growth factor-I(SM) circulates in plasma bound to a large molecular weight (150K) GH dependent protein complex (SM-BP). There is also a smaller (38K) non-GH dependent protein which binds exogenous radiolabeled SM. Although SM is GH dependent, children with certain nutritional disturbances show a dissociation between GH and SM. SM-BP was studied in 3 children with normal SM (by RIA) and normal growth rate inspite of documented GH deficiency. All are hyperphagic and obese; 2 are status-post craniopharyngioma resection; the third has arrested hydrocephalus. Insulin responses to oral glucose were elevated but prolactin levels were not. [125I] SM (20,000 cpm) was incubated (4°, 16 hrs) with 1 ml of plasma. The mixture was subjected to gel filtration (2.6 × 80 cm, Sephacryl-200, 0.1 M Tris, 5mM EDTA, pH 7.4). Endogenous SM eluted at Ve/Vo of 1.2-1.25 (≃150K). Some [125I] SM also eluted in this region while the major portion eluted at Ve/Vo of 1.5 (≃40K). This pattern of endogenous and [125I] SM was identical to that seen in normal adults and hyposomatotropic children on GH. These results indicate that 150K SM-BP is regulated in parallel with SM in those instances when SM and GH are discordant. Such closely coordinated regulation might be accomplished if SM and SM-BP were synthesized together.
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Blethen, S., Cohen, D. Somatomedin binding proteins in GH deficient children with normal somatomedin. Pediatr Res 15, 1545 (1981). https://doi.org/10.1203/00006450-198112000-00058
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DOI: https://doi.org/10.1203/00006450-198112000-00058