Clinical Assay of Somatomedins by RIA
The somatomedins (SM’s) are a group of growth-hormone-dependent insulin-like growth factors (IGF’s). The measurement of plasma concentrations of SM-C (IGF-I) in particular appears to have the greatest potential in clinical diagnosis, e.g. to assess growth hormone (GH) status in children; its level is more stable than that of GH, for reasons that are outlined.
The development of assay methodology has progressed from bioassay through receptor assay to immunoassay (Ik) as sufficient amounts of purified hormone became available to permit the production of antibodies (kb’s). The purified hormone being scarce, there is an alternative approach to kb production involving the use of synthetic fragments as immunogens. The resulting kb’s may exhibit sufficient cross-reaction with the whole peptide to permit the measurement of plasma SM-C levels in normal and acromegalic subjects. However, for adequate discrimination between normal and subnormal levels in young children, greater sensitivity is required. So far this has been achieved only with kb’s raised against the whole peptide. Variable interference by SM-binding proteins in Ik methods may necessitate the initial extraction of samples in order to standardize procedures.
KeywordsGrowth Hormone Carrier Protein Sulphate Incorporation Synthetic Fragment Growth Hormone Status
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