[Somatomedins. Structure, physiology and clinical data]

For an adequate interpretation of the significance of somatomedin levels in clinical conditions, a number of factors should be considered which may have an influence on the result. First of all, the heterogeneity of the somatomedins, both in their complexed form and after dissociation, should be considered. These forms have an unequal degree of cross-reactivity in different assay systems, while only the function of SM-C/IGF-I and, to a minor degree, of IGF-II have been established. Both are mitogenic and IGF-II has more insulin-like effects than does SM-C/IGF-I. Only the latter has been shown to increase length in dwarf mice. Somatomedins are produced in many tissues. This has led to the concept of autocrine or paracrine functions. The levels of SM-C/IGF-I increase with age, and there is a large increase during puberty, particularly when measured in the radioimmunoassay. In addition its level is influenced by growth hormone, to a minor degree by thyroid hormones, prolactin and perhaps by HCS and insulin. Finally, the nutritional and metabolic state of the patient is important: low values have been found in malnutrition, poorly regulated diabetes mellitus and insufficiency of the liver. Measuring somatomedins may be helpful for diagnosis and evaluation of the therapy of certain disorders, but the complexity of the regulation of their blood levels needs caution in the interpretation of results.