Anabolic Effects of Recombinant Human Growth Hormone and Insulin-Like Growth Factor I in Human Disease

Growth hormone (GH) and the insulin-like growth factor (IGF) hormonal system, along with insulin itself, play a major role in body anabolism. Growth hormone has long been known to have a major controlling influence on linear growth; in addition, it has well defined effects on protein, carbohydrate, lipid, and mineral metabolism (1). Many of the growth-promoting and metabolic effects of GH are not direct actions of GH on its target tissues, but actions mediated by insulin-like growth factor I (IGF-I) (2). IGF-I is homologous to insulin, and its synthesis is closely controlled by GH. IGF-I does not circulate free in plasma, but is almost all bound by a series of 6 IGF binding proteins that serve to prolong the half-life of IGF in serum, modulate its insulin-like effects, and control the delivery of IGF-I to receptors on target cells. The interaction of IGF-I with the type I IGF receptor (IGF-R) leads to a series of anabolic actions within the cells, including the synthesis of protein and other macromolecules and cell division (2).