SEXUAL STEROIDS AND BONE TISSUE

The precise mechanism of action of sexual steroids in the regulation o f bone tissue is still poorly understood. Besides the indirect action via the production of calciotropic hormones, the fact that receptors r espond to cestrogens as well as to androgens and progesterone is evide nce that sexual steroids have a direct action in regulating bone activ ity. The anti-osteoclastic action of cestrogens, via the modulation in osteoblastic production of different substances such as interleukin-1 and -6, TGF beta, GM-CSF which inhibit osteoclastogenesis and bone re sorption activity, is well documented. More recently, the direct role in osteoclast inhibition was suggested by the observation that osteocl asts carry cestrogen receptors. Likewise,certain in vivo and in vitro data suggest that cestrogens could also have a positive effect on bone formation regulation. For androgens, currently available data show th at in vitro stimulation of bone formation, with increased proliferatio n and cell differentiation, could be mediated by TGF beta. The role of progesterone is more recently known. In vivo, progesterone increases cell growth and IFGF-II secretion by nontransformed human osteoblasts. The number of potential mechanisms which have already been demonstrat ed suggest the complexity of sex hormone regulation which leads to the final situation of physiological calcium sparing in the skeleton whil e maintaining skeletal structure.