ESTROGEN AND BONE METABOLISM

Estrogen plays an important role in the growth and maturation of bone as well as in the regulation of bone turnover in adult bone. During bo ne growth estrogen is needed for proper closure of epiphyseal growth p lates both in females and in males. Also in young skeleton estrogen de ficiency leads to increased osteoclast formation and enhanced bone res orption. In menopause estrogen deficiency induces cancellous as well a s cortical bone loss. Highly increased bone resorption in cancellous b one leads to general bone loss and destruction of local architecture b ecause of penetrative resorption and microfractures. In cortical bone the first response of estrogen withdrawal is enhanced endocortical res orption. Later, also intracortical porosity increases. These lead to d ecreased bone mass, disturbed architecture and reduced bone strength. At cellular level in bone estrogen inhibits differentiation of osteocl asts thus decreasing their number and reducing the amount of active re modeling units, This effect is probably mediated through some cytokine s, IL-1 and IL-6 being strongest candidates, Estrogen regulates the ex pression of IL-6 in bone marrow cells by a so far unknown mechanism. I t is still uncertain if the effects of estrogen on osteoblasts is dire ct or is due to coupling phenomenon between bone formation to resorpti on.