摘要:

The insulin-like growth factor (IGF)-binding proteins present in the human serum and various biological media have been characterized by several methods: gel filtration, sucrose gradient sedimentation, polyacrylamide gel electrophoresis and chromatofocusing. Several forms have been identified with molecular weights of ∼ 42,000, 39,000, 34,000, 30,000 and 24,000 daltons. Results of competitive binding studies suggest that the different forms of binding proteins have different affinities for IGF-I and IGF-II. The influence of various hormones and pathophysiological conditions on the biosynthesis of the binding proteins has been investigate

ISSN:1663-2818    

DOI:10.1159/000180553

出版商:S. Karger AG    

年代:1986

数据来源: Karger

摘要:

The insulin-like growth factors IGF-I and IGF-II are mitogenic polypeptides with a high degree of chemical homology. Two distinct subtypes of receptors for the IGFs have been identified on the basis of structure and binding specificity. Type I IGF receptors bind IGF-I with equal or greater affinity than IGF-II, and also bind insulin with a low but definite affinity. They are structurally homologous to insulin receptors, containing disulfide-linked α-subunits that bind the peptides and β-subunits that have intrinsic tyrosine-specific kinase activity. Type II IGF receptors typically bind IGF-II with greater affinity than IGF-I, and do not interact with insulin. They consist of a single polypeptide and lack tyrosine kinase activity. Because of the extensive cross-reactivity of IGF-I and IGF-II with both type I and type II receptors, we believe that potentially either receptor may mediate the biological responses of either peptide. Type I IGF receptors have been shown to mediate the mitogenic effects of the IGFs in some cell types. Whether type II IGF receptors mediate the same or different functions remains to be elucidate

ISSN:1663-2818    

DOI:10.1159/000180554

出版商:S. Karger AG    

年代:1986

数据来源: Karger

摘要:

Except in acromegaly, where insulin-like growth factor I (IGF I) levels are elevated, only decreased IGF levels have been observed under pathophysiological conditions. These are hypopituitarism, Laron dwarfism, leprechaunism, liver disease, primary hypothyroidism, extrapancreatic tumor hypoglycemia and severe insulin deficiency in experimental animals. For most of these diseases the diagnostic value of IGF determinations is limited. IGF I determinations may serve as a useful additional diagnostic index in acromegaly and in the evaluation of successful operative and/or radiotherapy of this disease.

ISSN:1663-2818    

DOI:10.1159/000180555

出版商:S. Karger AG    

年代:1986

数据来源: Karger

摘要:

Nutritional intake is an important regulator of plasma somatomedin-C/insulin-like growth factor I (Sm-C/IGF-I) concentrations in plasma. Concentrations in humans are reduced to the hypopituitary range by fasting for only a few days, and their normalization after fasting depends on the adequacy of energy and protein in the refeeding diet. The changes correlate with changes in nitrogen balance. In rats we have observed a close relationship between change in plasma Sm-C/IGF-I and hepatic GH binding with fasting and refeeding, suggesting that alterations in GH binding might be responsible partly for changes in Sm-C/ IGF-I. When malnourished humans are given nutrient repletion, the increase in Sm-C/ IGF-I is far more dramatic than changes in other nutrient-related serum proteins.

ISSN:1663-2818    

DOI:10.1159/000180556

出版商:S. Karger AG    

年代:1986

数据来源: Karger

摘要:

Normal growth during childhood and adolescence is a complex process which requires the participation of a number of hormones and growth factors. Sm-C/IGF-I plays a central role in this process, with variations in both its serum concentration and the cellular responsiveness to it being important mechanisms regulating growth.

ISSN:1663-2818    

DOI:10.1159/000180557

出版商:S. Karger AG    

年代:1986

数据来源: Karger

摘要:

Somatomedin levels measured by radioreceptor assay, competitive protein-binding assay or radioimmunoassay are normal in hypercortisolism; the decrease of somatomedin activity consistently found in this condition is due to an increase in circulating somatomedin inhibitors resulting in an inhibition of somatomedin action. Progestagens could possibly have a direct stimulatory effect on somatomedin-C (Sm-C) production. During puberty, the increase of Sm-C is correlated with the increase in plasma estradiol and testosterone. In young subjects, relatively low doses of estrogens and of testosterone enhance Sm-C secretion, and in adult menstruating women, a positive relationship is found between testosterone and Sm-C values. An inhibitory effect of estrogens on Sm-C is observed with higher doses and/or in older subjects. Thus, somatomedin levels might be modulated by variations of sex steroids.

ISSN:1663-2818    

DOI:10.1159/000180558

出版商:S. Karger AG    

年代:1986

数据来源: Karger

ISSN:1663-2818    

DOI:10.1159/000180559

出版商:S. Karger AG    

年代:1986

数据来源: Karger

ISSN:1663-2818    

DOI:10.1159/000180560

出版商:S. Karger AG    

年代:1986

数据来源: Karger