[Anabolic action of PTH under the loading/unloading condition]

Parathyroid hormone (PTH) is available for the treatment of osteoporosis in Japan. PTH is administered subcutaneously daily or weekly. According to the results of animal experiments, the anabolic action of PTH on bone depends on dosage, condition of loading, and region of bone. Administration of PTH preserved trabecular bone formation rate reduced by immobilization or unloading at the same level of that under the normal mobilization or loading condition, but at low dose did not preserve periosteal bone formation rate reduced by unloading. PTH at high dose (40μg/kg BW) completely preserved trabecular bone volume reduced by immobilization in mice. Thus, we consider that PTH could be clinically effective for immobilization- and/or unloading-induced bone loss.