Implanted octacalcium phosphate (OCP) stimulates osteogenesis by osteoblastic cells and/or committed osteoprogenitors in rat calvarial periosteum

Our previous studies demonstrated that the octacalcium phosphate (OCP) caus es new appositional bone formation on the OCP when implanted into the subpe riosteal region of murine calvaria. The OCP may stimulate the cell populati on committed to the osteoblastic differentiation in the periosteum and have them express the phenotype. The present study was designed to investigate which periosteal cell population is involved in bone formation on the OCP w ith applying the OCP implants on top of and underneath the periosteum. The periosteum of the rat parietal bones was flapped and the OCP was implanted on top of or underneath the periosteum, in which the implantation sites wer e defined using the membrane filter. The histology was examined to see if n ew appositional bone formation occurs on the OCP implant under each conditi on. New bone was deposited on the OCP on the bone surface separated from th e periosteum by the filter, whereas no bone was formed either under the per iosteum separated from the bone surface by the filter or on the periosteum. The present study suggests that the OCP acts on osteoblasts, bone lining c ells and/or their closely committed progenitors on the bone surface to expr ess the phenotype and deposit new bone on the OCP implant. Anat Rec 256:1-6 , 1999. (C) 1999 Wiley-Liss, Inc.