Growth hormone, skeletal growth factors and osteoporosis.

Bone remodeling is regulated by systemic hormones and growth factors acting in concert to maintain normal bone mass. Growth hormone has important effects on bone metabolism and acts by stimulating the production of insulin-like growth factor (IGF) I in the liver. Conditions of growth hormone deficiency have decreased bone mass that could be modified by growth hormone administration. Skeletal cells synthesize a variety of growth factors with diverse properties and levels of regulation. IGF I and II seem to play a major role in the local regulation of bone remodeling, and other growth factors have important mitogenic properties. Skeletal growth factors may be regulated at the level of synthesis, activation, receptor binding or binding proteins. Growth factors such as IGF I could be considered for the systemic treatment of various bone disorders, or drugs could be developed to modify the synthesis or activity of the locally produced factors. Additional research should result in the development of novel approaches to the treatment of osteoporosis.