[PTH and mechanical stress].

Intermittent administration of PTH increases bone mass by enhancing bone formation. Several mechanisms have been demonstrated for this effect of PTH on bone formation such as the enhancement of Wnt signaling as well as the stimulation of differentiation and the inhibition of apoptosis of cells in the osteoblast lineage. Because mechanical loading to bone also enhances bone formation at least in part through the stimulation of Wnt signaling, it has been anticipated that the intermittent PTH is useful for the prevention of bone loss by mechanical unloading. However, results so far obtained in animal models have indicated that PTH can not completely abolish the deleterious effect of unloading on bone mass. It is necessary to search new drugs that show more potent effect on bone formation and also to investigate the mechanism of action of mechanical loading on bone.