Measurement of serum insulin-like growth factor 2 (IGF-2) is used as an adjunct to IGF-1, in the clinical evaluation of growth hormone-related disorders.
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Insulin-like growth factor 2 (IGF-2) is a 7.5 kD, 67 amino acid peptide which is thought to mediate some of the actions of growth hormone (GH). IGF-2 peptide is structurally homologous to IGF-1 and proinsulin. IGF-2 is secreted mainly by the liver and other tissue and is postulated to have mitogenic and metabolic actions. The growth factor has a major, but not absolute, dependence on somatotropin. It is believed to be a major fetal growth factor in contrast to insulin-like growth factor 1 (IGF-1), which is a major growth factor in adults. IGF-2 circulates primarily in a high molecular weight complex with IGF-binding protein-3 (IGFBP-3). A smaller proportion of IGF-2 may circulate in association with other IGF-binding proteins or as unbound IGF-2. Plasma levels of IGF-2 are dependent upon adequate levels of GH and other factors, including adequate nutrition.
The actions of IGF-2 are mediated by binding to specific cell surface receptors. IGF-2 binds with lower affinity to the IGF-1 type receptors and the insulin receptors. These latter receptors may mediate the mitogenic and metabolic actions of IGF-2. Although its specific physiologic role has not been defined, it has been postulated that the interplay of IGF-1 and IGF-2 with the different cell surface receptors and circulating binding proteins modulate tissue growth.
Normal postnatal plasma IGF-2 levels are assumed to be at maximum levels. Postnatal plasma IGF-2 levels show a moderate age-related increase throughout childhood and puberty, and there is no significant variability during the day. IGF-2 levels decrease in GH deficiency and in malnutrition. IGF-2 levels may also decrease in acromegaly and during exogenous administration of IGF-1.
