Which statement accurately describes insulin-like growth factor (IGF-1) in relation to growth hormone?

Which statement accurately describes insulin-like growth factor (IGF-1) in relation to growth hormone?

• A. IGF-1 is produced by the liver in response to growth hormone
• B. IGF-1 is produced by the pituitary
• C. IGF-1 inhibits growth
• D. IGF-1 has no relation to growth hormone

Answer: (A)

Growth hormone promotes most of its growth effects through a downstream mediator produced mainly by the liver. When growth hormone stimulates hepatic cells, they release IGF-1 into the bloodstream. This circulating IGF-1 drives growth by stimulating bone growth at the growth plates and increasing protein synthesis in various tissues, making it the primary mediator of GH’s effects on growth. Growth hormone does have direct actions too, but IGF-1 carries the major growth-promoting signal. IGF-1 also participates in a feedback loop that helps regulate GH release, tempering further secretion from the pituitary. Therefore, IGF-1 is produced by the liver in response to growth hormone, and it promotes growth rather than inhibiting it.

Growth hormone promotes most of its growth effects through a downstream mediator produced mainly by the liver. When growth hormone stimulates hepatic cells, they release IGF-1 into the bloodstream. This circulating IGF-1 drives growth by stimulating bone growth at the growth plates and increasing protein synthesis in various tissues, making it the primary mediator of GH’s effects on growth. Growth hormone does have direct actions too, but IGF-1 carries the major growth-promoting signal. IGF-1 also participates in a feedback loop that helps regulate GH release, tempering further secretion from the pituitary. Therefore, IGF-1 is produced by the liver in response to growth hormone, and it promotes growth rather than inhibiting it.