Growth metabolism

Serum, plasma

Samples have to be chilled as soon as possible after collection. Stable for 3 days at RT. Long-term storage should be carried out at –20°C or below. Avoid repeated freezing/thawing of specimens.

Human

The Insulin-like Growth Factors (IGF) – I and II are bound to specific binding proteins (IGFBP) in circulation. Until today seven different proteins have been identified: IGFBP-1 to 7. IGF bioavailability, transport and storage is regulated or facilitated by these binding proteins which are expressed differentially according physiological and developmental requirements. The most abundant IGFBP in circulation is IGFBP-3. Together with IGFBP-5 it is able to form the so called ternary complex with IGF and the acid-labile subunit (ALS). In the circulation nearly all IGF is bound in this ternary complex and thus not able to cross the endothelial barrier. Only very small amounts of IGF or IGFBP-3 exist outside this complex. The acid-labile subunit is an important part of the IGF-storage mechanism in circulation. In ALS deficiency or in ALS knock-out mice the concentration of IGF and IGFBP-3 in the circulation is significantly decreased resulting in impaired growth. Beside growth also other endocrine axes may be involved. In primary ALS deficiency hyperinsulinemia could be observed. Further, the HGH-IGF-IGFBP system seems to be of relevance in coronary disease.
ALS can be used as supplementary information in GH-diagnostics together with IGF-I and IGFBP-3 measurements. Thus, it is of use in evaluation of GH-deficiency and excess.