Abstract
Somatomedin-C, isolated in our laboratory, has been radio-iodinated and studied for its binding to human placental plasma membranes. Under optimal conditions, up to,20% of the labeled hormone is specifically bound to the receptor. The curves of competition for the somatomedin (SM) receptor produced by unextracted reference plasma paralleled those produced by a SM standard. Differences in the SM activity between hypopituitary dwarfs and normal children were readily apparent when 2-10 μl of plasma were compared to the reference plasma. The mean relative SM concentration for the 21 dwarfs was 0.35 ± 0.33 (1 S.D.), whereas the concentration for 19 normals was 1.21 ± 0.62. Administration of hGH to a hypopituitary dwarf induced a 3-fold increase in activity.
The SM receptor assay, when used in conjunction with a placental receptor assay using radioiodinated insulin, provides a rapid method for monitoring purification of SM peptides. The SM receptor is more sensitive to SM, but the insulin receptor recognizes a greater variety of insulin-like peptides. The placental insulin receptor cannot detect differences between hypopituitary and normal serum.
These results suggest that under physiologic conditions, somatomedin is preferentially bound to its own receptor rather than to the receptor shared with insulin.
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Underwood, L., Marshall, R., Voina, S. et al. UTILIZATION OF RADIORECEPTOR ASSAYS FOR QUANTITATION OF SOMATOMEDIN AND INSULIN-LIKE PEPTIDES IN PLASMA AND PLASMA EXTRACTS. Pediatr Res 8, 376 (1974). https://doi.org/10.1203/00006450-197404000-00218
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DOI: https://doi.org/10.1203/00006450-197404000-00218