The physiological role of IGFBP-1

It appears that a readily available pool of IGF is achieved by IGFBPs, primarily IGFBP-3, that maintain a relatively constant high level of IGF. A circulating enzyme is present in the circulation which can modify IGFBP-3. When IGF levels are low this enzyme may be activated to alter the availability of the limited reserves of IGF to the tissues. In conditions where fuel supplies are compromised IGF-actions can be modulated by acute changes in IGFBP-1 levels. The extent to which IGFBP-1 acts by affecting IGF transport to the tissues or by affecting its activity in the tissues has still to be determined. However, this is still a simplistic concept of a system where there is much more yet to be understood. There are several IGF-binding proteins whose physiology is largely uncharacterized, and possible interactions between the various components of the system are still largely unexplored.