[Hormonal regulation of bone remodeling]

In the adult skeleton a continuous turnover of bone matrix and mineral takes place at discrete foci throughout life (bone remodeling). This process ensures the mechanical integrity of the skeleton and plays an important role in calcium homeostasis. It constitutes a very complex sequence of events, involving activation of several different stem cell populations and rigid regulation of two contrasting processes: bone resorption and bone formation. The study of factors involved in the control of bone remodeling is complicated by the involvement of local factors (growth factors, prostaglandins, inorganic ions) and systemic factors (calcitropic hormones), that interact at several different levels (cellular, tissue, and organ-levels). Most metabolic bone diseases, including osteoporosis, are caused by disturbances in the regulation of bone remodeling leading to an imbalance between resorption and formation. To understand these disturbances fully, it is necessary to study the different levels of skeletal organization, and the effect of different hormones and local factors on bone resorption and formation. In this review are described the effects of calcitropic hormones on bone cells at the cellular and tissue levels, and their interaction with local factors.