Insulin-like growth factor 1
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Insulin-like growth factor 1 (IGF-1) is a protein hormone similar in molecular structure to insulin. IGF1 plays an important role in childhood growth and continues to have anabolic effects in adults.
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Production and circulation
IGF1 is produced by the liver and target tissues. Production is stimulated by growth hormone and retarded by undernutrition. A large fraction of circulating IGF1 is attached to IGF binding proteins.
Action
Its primary action is mediated by binding to specific IGF receptors present on many cell types in many tissues. The signal is transduced by intracellular events. The effect is the promotion of cell growth and multiplication.
Almost every cell in the human body is affected by IGF-I, especially cells in muscle, cartilage, bone, liver, kidney, nerves, skin, and lungs. In addition to the insulin-like effects, IGF-I can also regulate cell growth and development, especially in nerve cells, as well as cellular DNA synthesis.
IGF1 is produced throughout life. The highest rates of IGF1 production occur during the pubertal growth spurt. The lowest levels occur in infancy and old age.
Use as a diagnostic test
IGF1 levels can be measured in the blood in 10-1000 ng/ml amounts. As levels do not fluctuate greatly throughout the day, IGF1 is used by physicians as a screening test for growth hormone deficiency and excess.
Diseases of deficiency and resistance
Rare diseases characterized by inability to make or respond to IGF1 produce a distinctive type of growth failure termed Laron dwarfism which does not respond well to growth hormone treatment.
IGF1 as a therapeutic agent
IGF1 has been synthesized and used in therapeutic trials for several conditions including growth failure and diabetes. The trials were not successful enough to warrant production and marketing by the company that sponsored the original trials, but a new company is again producing it and sponsoring new clinical trials for growth failure in the US.
Terminology
IGF1 was known as "nonsuppressible insulin-like activity" (NSILA) in the 1970s, and as somatomedin C in the 1980s.