IGF-1 (Insulin-like growth factor 1)

Definition

Insulin-like growth factor 1 (IGF-1) is a 70-amino acid peptide hormone that mediates many of the growth-promoting effects of growth hormone (GH). IGF-1 is produced predominantly in the liver in response to GH stimulation, but it is also produced locally in many tissues. Circulating IGF-1 acts on target tissues to promote cell growth, proliferation, and survival; it also has metabolic effects on glucose and lipid homeostasis. IGF-1 also provides negative feedback to the hypothalamus and pituitary, inhibiting the release of GHRH and GH. This feedback loop is important for maintaining appropriate GH levels. Serum IGF-1 concentration is often used as a marker of GH status; low IGF-1 levels suggest GH deficiency, while elevated levels suggest excess GH. Research investigating GH secretagogues and GHRH analogues often measures IGF-1 as a key outcome because IGF-1 production is a primary mechanism through which GH produces its growth-promoting effects. Dysregulation of IGF-1 (either too high or too low) can have significant metabolic and physiological consequences.

IGF-1 is structurally similar to insulin (hence the name), but it binds primarily to the IGF-1 receptor rather than the insulin receptor, though there is some cross-reactivity. The IGF-1 receptor is expressed in many tissues, allowing IGF-1 to exert widespread effects on growth, metabolism, and cell survival. In research studies, both GH and IGF-1 concentrations are typically measured because they provide complementary information about the GH axis; GH levels show the immediate pituitary response to a secretagogue, while IGF-1 levels reflect the integrated GH effect over hours to days (IGF-1 has a much longer half-life than GH).

Age-related changes in IGF-1 have been a focus of research investigating the aging process and interventions to promote healthy aging. IGF-1 levels decline with age, and some age-related conditions (such as loss of muscle mass) correlate with lower IGF-1. However, elevated IGF-1 may increase cancer risk in some populations, creating a complex relationship between IGF-1 levels and health outcomes. Research investigating compounds that alter GH and IGF-1 levels must measure both hormones and assess whether changes produce beneficial or adverse metabolic effects.