[22] Somatomedin C/insulin-like growth factor I receptors on human mononuclear cells and the IM-9 lymphoid cell line

Publisher Summary Somatomedin C (Sm-C) is a basic hormonal peptide that is under the control of growth hormone (GH) and is responsible for many, if not all, of the growth-promoting actions of GH. Like other hormonal peptides, the receptors for Sm-C/IGF-I are mainly on the outside of the cellular membrane. The measurement of these receptors allows insight into a crucial step in the action of the Sm-C/IGF-I peptides and thus into the control of cellular growth. The number of receptors on circulating human blood cells, in particular the mononuclear cells, changes with the circulating concentration of Sm-C/IGF-I and reflects the dynamics of changes of Sm-C/IGF-I receptors throughout the body. This chapter discusses the receptors on human mononuclear cells. Recently, a synthetic preparation of IGF-I has been manufactured by AMGEN Corporation (Thousand Oaks, CA, Amershaw International). This biosynthetic IGF-I has exactly the same structure as natural Sm-C/IGF-I purified from human plasma with the exception of a threonine substituted for methionine at position 59. The Sm-C/IGF-I, either native or synthetic, is iodinated by the modification of the chloramine-T method using a limited amount of chloramine-T and without the use of sodium metabisulfite. The mononuclear cells are isolated by the method of Boyum.