The insulin-like growth factor-binding proteins (IGFBPs) are carrier proteins that are present in all extracellular fluids (1 ). Similarly, insulin-like growth factor-I (IGF-I) and -II are synthesized by connective tissue cells that are present within the stroma of all tissues, and therefore their presence is ubiquitous in all organs (2 ). IGF receptors are present in all tissues, which accounts for balanced growth of organs, and deletion of theIGF-Igene results in a balanced decrease in organ growth, whereas overexpression ofIGF-Iresults in a symmetric increase in growth (3 ).
