Role of prostaglandins in bone resorption in a synchronized remodeling sequence in the rat

The role of prostaglandins (PGs) in physiological remodeling has not yet been defined. The present study was undertaken to determine whether they intervene during the activation phase in a highly reproducible and synchronized model of bone remodeling. Indomethacin was employed to inhibit PG synthesis. This treatment throughout the entire activation period (4 days in this model) inhibited osteoclastic resorption completely. By modifying the treatment procedure, it appeared that PGs were operative mainly between the second and third day of activation. PGs did not seem to act on precursor recruitment, since off-bone osteoclasts (putatively inactive cells) were numerous in the treated groups. PGs might also be involved in osteoclast activity as the mean interface between osteoclasts and bone surface was reduced in the treated groups. However, indomethacin was unable to inhibit the remodeling sequence durably since a 6-day treatment resulted in a high profile of resorption. This suggests that factors other than PGs were responsible for activating resorption.