IGF-1 (Insulin-like growth factor 1), also called somatomedin C, is similar to insulin. It is a hormone that has been shown to play a role in the growth of young mammals and has anabolic effects on adult animals.
It synthesizes as an endocrine hormone and the target organ as a paracrine or autocrine hormone. It is produced throughout one’s lifetime and is highest in animals during adolescence and lowest in babies and the elderly.
Structure of Insulin-like Growth Factor 1 (IGF-1)
It is a small peptide consisting of 70 amino acids with a molecular weight of 7649 Da. The disulfide bonds of IGF-1 link the alpha and beta chains. Rat IGF-1 synthesizes as four precursor isoforms with alternating N-terminal and C-terminal propeptides. Mature IGF-1 is identical between isoforms, and cleavage of the propeptide terminal produces it. There are 12 amino acids in the C-peptide region.
Mechanism of Action
Studies of laboratory animals have shown that IGF-1 is a significant mediator of growth hormone action. The pituitary gland produces Growth Hormone, and it circulates in the bloodstream to cause the liver to produce IGF-1.
IGF-1 binds to at least two of the receptors of cell membrane tyrosine kinases, including the IGF-1 receptor and the insulin receptor. Its main action is binding to the IGF-1 receptor, which is ubiquitous in tissues. This ligand-receptor complex stimulates cell growth and proliferation and emits intracellular messages via the AKT pathway known to inhibit programmed cell death.
Insulin can also bind to the IGF-1 receptor. Still, its affinity is much lower, and IGF-1 can also bind to the insulin receptor to produce a 10% effect of insulin’s potency. Insulin growth factor 1 interacts with all seven IGF-1 binding proteins, specifically IGFBP2 and IGFBP5, and these two serum levels are inversely proportional to circulating IGF-1.
Blood-transported IGF-1 regulates balanced growth across many tissues and organs. Stimulation of autocrine or paracrine IGF-1 can cause excessive growth as it works unaffected by growth hormone.
Insulin-like Growth Factor-1 (IGF-1) Effects
The first demonstration of the growth-stimulating effect of extrinsic IGF-1 occurred by administering a purified hormone to hypophysectomy rats.
● In diabetic rats, it helps control glucose, and efficacy is inversely proportional to the duration of diabetes.
● In vivo administration of IGF-1 showed anabolic effects with subsequent rapid growth in neonatal rats, but there is evidence that complete expression at a given dose requires nutrition.
● Exogenous administration of IGF-1 induced hepatoprotective and antifibrinolytic effects in experimental
cirrhosis. These effects were associated with decreased liver levels of several factors involved in oxidative damage, such as myeloperoxidase and nitric oxide.
● Obstruction of the right middle cerebral artery induces ischemia, and IGF-1 expression in the central nervous system reduces significantly. Intramuscular IGF-1 injection increased expression in the affected muscles, sciatic nerve, lumbar spinal cord, and motor cortex. This reduced neuronal apoptosis and improved motor function.
● Immunohistochemical analysis of rat testes of various ages revealed increased IGF-1 receptors from birth to 20 days after delivery. Tests have shown that IGF reduces the level of Leydig cell apoptosis at all stages of development.
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