[Recent data on somatomedins (insulin-like growth factors) (author's transl)]

Data on somatomedins have resulted from the convergence of two initially distinct lines of research relating to the two major aspects of their biological activities, their effects on cartilage growth and their insulin-like action. Human serum has yielded three factors, SM-A, SM-C and NSILA-S. The latter comprises two very similar polypeptides, IGF I and IGF II which structurally closely resemble proinsulin. A fourth factor, MSA, has been isolated from calf serum and from conditioned medium of a rat liver cell strain. All these chemically and biologically closely related factors have a molecular weight of approximately 7 500 but circulate in a form with much higher molecular weight owing to their binding to specific carrier proteins. Over the past five years, the use of purified somatomedins has led to rapid progress in the elucidation of the physiology of these hormones. In this review, present knowledge of somatomedins is analysed in the following terms: physiochemical properties, circulating forms, action on growth, insulin-like activity, interaction with receptors, immunological characteristics, biosynthesis and hormonal regulation of their blood level. Results obtained in our laboratory from rat liver organ culture are discussed: the action of culture media on cartilage sulphation, the detection of a protein which specifically binds NSILA-S and SM-A and its use in a competitive protein binding assay for somatomedins in biological fluids.