Androgens and bone.

Androgen receptors are present at low densities in osteoblasts. Androgens are also metabolized in bone. (Non)aromatizable androgens probably induce proliferation of osteoblasts and differentiation. A direct effect of androgens on osteoclasts has not been demonstrated. Androgens may however inhibit bone resorption indirectly, by an inhibition of the recruitment of osteoclast precursors from bone marrow, by decreased secretion of interleukin-6 and/or prostaglandin E2, and/or by an increased sensitivity of marrow cells or osteoblasts for bone resorption stimulating factors such as PTH. The recent demonstration of androgen receptors in bone marrow stromal and osteoclast-like cells opens new perspectives in this respect. During puberty, androgens stimulate bone growth both directly and indirectly. Observations in androgen-resistant animals clearly demonstrated that the sexual dimorphism of bone depends on the presence of a functional androgen receptor. Optimal peak bone mass seems related to an appropriately timed androgen secretion. In adults, androgens are also involved in maintenance of the male skeleton. Androgen replacement may prevent further bone loss in hypogonadal men, however, it seems difficult to fully correct bone mass in these men.