Research on somatomedins (insulin-like growth factors) has progressed greatly over the past few years. In the present review we summarize, in addition to our own results, some recent findings concerning the structure of these factors, their carrier protein, their biosynthesis and hormonal regulation. We also stress the interest of specific assays for their use in clinical investigation.

Acromegaly↗

PubMedDate not supplied

[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.

Adipose Tissue↗

PubMedDate not supplied

[Biosynthesis and hormonal regulation of IGF (insulin-like growth factors, or somatomedins). Experimental and clinical studies (author's transl)].

Rat liver explants in culture release into the culture medium IGF and their carrier which form a complex with an apparent molecular weight of similar to or approximately 40,000. With gel filtration in acetic acid the IGF are separated from their carrier and each can then be measured by radioligand assay. In terms of their hormonal control "in vitro", GH, insulin and cortisol have an independent action on each. Pituitary and various brain tissues in organ culture also produce IGF and their carrier. The "in vitro" regulation of the IGF and their carrier has been investigated through assays of their levels in human serum under normal and pathological conditions, such as hypopituitarism, acromegaly, coeliac disease, Cushing's syndrome and idiopathic short or tall stature.

Acromegaly↗

PubMedDate not supplied

[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.

Adult↗