[Competitive protein-binding assay for somatomedins and their carrier protein (author's transl)]

Rat liver explants in culture release a protein which has a molecular weight of approximately 65,000 and both an affinity and a specificity for somatomedins (SMs) similar to that of the carrier protein found in human serum. A competitive binding assay has been set up using this protein and purified NSILA-S, with a sensitivity threshold of 0.05 mu U NSILA-S. By means of gel filtration in acetic acid of the biological samples, SMs and their carrier protein are separated and the two parameters can therefore be measured within the same sample. Purified preparations of NSILA-S and SM-A, and endogenous SMs extracted from various mammalian sera and from rat liver culture medium give parallel dose-response curves. The mean SM concentrations in human serum, expressed in terms of mu U NSILA-S/ml were 199 +/- 10.8 (SE) in 9 normal adults, 19 +/- 2.7 in 18 hypopituitary patients and 255 +/- 14 in 18 acromegalics. Compared with the levels in normal subjects, acromegalic had high, and hypopituitary patients low carrier protein concentrations.