Insulin-Like Growth Factor 1 (IGF-1)
A hormone structurally similar to insulin that mediates many of growth hormone's effects in the body. IGF-1 is primarily produced by the liver in response to GH stimulation and serves as the key clinical biomarker for assessing growth hormone activity and treatment adequacy.
Technical Context
IGF-1 is a 70 amino acid polypeptide with approximately 50% structural homology to insulin. It circulates primarily bound to IGFBP-3 and the acid-labile subunit (ALS), forming a ternary complex with a half-life of approximately 12-16 hours (compared to minutes for free IGF-1). Serum IGF-1 levels are age- and sex-dependent, peaking during puberty and declining thereafter. Clinically, IGF-1 measurement is used to: diagnose GH deficiency (low IGF-1) and acromegaly (elevated IGF-1), titrate GH replacement therapy to age-appropriate levels, and monitor response to somatostatin analogues in acromegaly (target: normalised IGF-1). IGF-1 acts through the IGF-1 receptor (a tyrosine kinase receptor distinct from GPCRs) to promote cell proliferation, differentiation, and survival.