INHIBITION OF PROSTAGLANDIN SYNTHESIS LEADS TO A CHANGE IN ADHERENCE OF MOUSE OSTEOCLASTS FROM BONE TO PERIOSTEUM

When mouse parietal bones were incubated for 1 day in medium containin g indomethacin (Ind), the number of tartrate-resistant acid phosphatas e-positive osteoclasts (TRAP+OC) counted on the bone surface was drast ically reduced. This reduction did not occur with calcitonin or if the endocranial membrane (periosteum) was removed prior to incubation wit h Ind. The aim of this work was to determine the mechanism involved. T RAP+OC were found to be increased on the endocranial membrane adjacent to the resorbing surface after Ind treatment, compared with cultures supplemented with parathyroid hormone (PTH) or prostaglandin E2 (PGE2) . However, this increase accounted for only half of those lost from th e bone surface. TRAP negative osteoclasts were also seen on the membra ne and, to a lesser extent, on the bone. Increased TRAP specific activ ity could be extracted from the endocranial membranes of bones incubat ed with Ind compared with PGE2 controls. When bones that had been expo sed to Ind were then cultured for 1 day in PGE2, an increase in TRAP+O C occurred. This increase was blocked by the removal of the endocrania l membrane prior to incubation with PGE2. We conclude that when prosta glandin production ceases, TRAP+OC become less adherent to bone and mo re adherent to the endocranial membrane.