Insulin-like growth factors/somatomedins: structure, secretion, biological actions and physiological role.

Insulin-like growth factors (IGFs, somatomedins) are structural homologues of insulin with insulin-like biological activity. They are mainly synthesized and secreted by the liver, but may also be produced by extrahepatic tissues. In their native from in blood they are bound to specific carrier protein(s). This determines essentially their biological actions. The complexed factors stimulate growth indices in vitro and in vivo, but, in contrast to the free factors, do not exert acute effects on insulin target tissues.