A RECEPTOR ASSAY FOR SOMATOMEDIN‐LIKE ACTIVITY USING MULTIPLICATION‐STIMULATING ACTIVITY (MSA) AS RADIOLIGAND

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Abstract
Multiplication-stimulating activity (MSA) in the medium of cultured rat liver cells was purified 120-fold by chromatography on Dowex 50W and Sephadex G 50. MSA was labelled with 125I-iodine and bound to a human placental membrane receptor. An assay for somatomedin-like receptor activity (SmLRA) in unextracted serum was based on the displacement of 125I-MSA from the placental receptor. The mean (precision) was 0063, sensitivity was < 0006 SmLRA units and interassay variation was 18%. The mean ( S.D.) SmLRA concentrations in 13 normal subjects, 7 growth hormone deficient patients and 8 patients with active acromegaly were 086 019, 034 008 and 234 082 U/ml, respectively. This assay may have potential clinical application in disorders of growth hormone secretion.