Somatomedins: insulin-like growth factors binding proteins

LBM includes skeletal muscle, somatic protein, and functional proteins such as circulating proteins and the visceral proteins. Biochemically, LBM can be assessed by measuring the serum visceral proteins, albumin (ALB), transferrin (TFN), and prealbumin (thyroxine-binding prealbumin or transthyretin). Other serum proteins, such as retinol-binding protein, flbronectin (an opsonic protein), and somatomedin-C (insulin-like growth factor-1), that have a very short half-life (less than 12 to 24 hours), have been suggested as... 

Insulin-like growth factors (IGF) have been shown to enhance hepatic amino acid transport as well. Actually, there are two major forms of IGF which, in the human, are called IGF-I and IGF-II. The corresponding proteins in the rat have been identified as somatomedin G and multiplication-stimulating factor (MSA). There are specific receptors for IGF-I and IGF-II in the plasma membrane of eukaryotic cells, although the IGF-I receptors show some affinity for IGF-II and vice versa (46). Furthermore, Massague and Czech (46) have shown that the IGF-I receptor exhibits some, albeit weak, affinity for insulin, whereas the IGF-II receptor does not bind insulin to a significant extent. Those authors have also demonstrated that rat liver lacks IGF-I (somatomedin C) receptors, so MSA would appear to play a more important role than somatomedin C in the regulation of hepatic metabolism in this species. 

Ginsberg, B. H., Kahn, C. R., Roth, J., Megyesi, K., and Baumann, G., 1979, Identification and high yield purification of insulin-like growth factors (nonsuppressible insulin-like activities and somatomedins) from human plasma by use of endogenous binding proteins, J. Clin. Endocrinol. Metab. 48 43. 

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