Nitric oxide and bone.

Age-associated decrease in nitric oxide (NO) production may be related to an increase in cardiovascular events, sexual dysfunction, and osteoporosis. Relative NO deficiency is a plausible biological basis for NO replacement therapy. Hormone replacement therapy (HRT) enhances local NO production and rectifies NO deficiency in postmenopausal women. However, excess local production of NO aggravates bone destruction in inflammatory arthropathies. In addition to its use in alleviating angina and erectile dysfunction, NO compounds could be a valuable supplemental therapy for chronic conditions including osteoporosis. Estrogen mediates its beneficial effects in bone, in part via the NO/cGMP pathway; hence NO donor therapy is an alternative to estrogen, estrogen agonists-antagonists, and androgen receptor modulator therapy in the prevention and treatment of osteoporosis. Large numbers of animal studies and human pilot studies support the concept of using NO donors for preventing bone loss. Administration of exogenous NO or prolonging endogenous NO activity are practical ways to supplement NO.