Expression of IGF-I in Liver
Insulin-like growth factor I(IGF-I) is a basic, 70 amino acid polypeptide with strong structural homologies to insulin. It has been shown to be critical in promoting skeletal growth during childhood and adolescence(Merimee et al., 1987) but available evidence suggests it is a multifunctional peptide hormone. It influences the differentiation of several cell types and can have insulin-like effects in certain circumstances. It is expressed in many tissues and in all probability exerts its growth-promoting and other effects by endocrine, paracrine, and autocrine mechanisms. In the last decade it has become evident that the liver is the primary source of circulating IGF-I in serum although the relative importance of serum-borne and locally synthesized IGF-I is not yet clear. In this essay, we will discuss the regulation of IGF-I expression in liver as it has been studied in various systems, including results from our own laboratory. A number of different models have been used to study hepatic IGF-I expression. These include:(1) In vivo models, principally hypophysectomized rats or the growth hormone(GH) deficient mouse strain C57BL lit/lit; (2) the isolated, perfused rat liver; (3) studies in organ culture; (4) primary hepatocyte cultures; and recently (5) studies employing transgenic mice.
KeywordsGrowth Hormone Growth Hormone Administration Primary Hepatocyte Culture Hepatic Growth Hormone Receptor Growth Hormone Infusion
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