Which mediator is primarily responsible for the growth-promoting effects of growth hormone?

Which mediator is primarily responsible for the growth-promoting effects of growth hormone?

• A. Growth hormone
• B. Corticotropin-releasing hormone
• C. Somatomedin
• D. Somatostatin

Answer: (C)

Growth-promoting effects of growth hormone are carried mainly through somatomedins, the insulin-like growth factors. When growth hormone acts on the liver (and other tissues), it stimulates production of IGF-1, a key somatomedin. IGF-1 then circulates and binds to IGF receptors on target cells, especially chondrocytes in the growth plates and various body tissues, triggering signaling pathways that promote cell proliferation, differentiation, and protein synthesis. This indirect route is the primary mechanism by which GH drives growth. Somatostatin simply inhibits growth hormone release, corticotropin-releasing hormone drives ACTH release, and growth hormone itself is the hormonal signal, not the mediator of the growth effects. Somatomedin (IGF) is the best answer because it is the principal mediator of GH’s growth-promoting actions.

Growth-promoting effects of growth hormone are carried mainly through somatomedins, the insulin-like growth factors. When growth hormone acts on the liver (and other tissues), it stimulates production of IGF-1, a key somatomedin. IGF-1 then circulates and binds to IGF receptors on target cells, especially chondrocytes in the growth plates and various body tissues, triggering signaling pathways that promote cell proliferation, differentiation, and protein synthesis. This indirect route is the primary mechanism by which GH drives growth.

Somatostatin simply inhibits growth hormone release, corticotropin-releasing hormone drives ACTH release, and growth hormone itself is the hormonal signal, not the mediator of the growth effects. Somatomedin (IGF) is the best answer because it is the principal mediator of GH’s growth-promoting actions.