Differential Stimulation of Prostaglandin G/H Synthase-2 in Osteocytes and Other Osteogenic Cells by Pulsating Fluid Flow

Mechanical stress produces flow of fluid in the osteocytic lacunar–canalicular network, which is likely the physiological signal for the adaptive response of bone. We compared the induction of prostaglandin G/H synthase-2 (PGHS-2) by pulsating fluid flow (PFF) and serum in osteocytes, osteoblasts, and periosteal fibroblasts, isolated from 18-day-old fetal chicken calvariae. A serum-deprived mixed population of primarily osteocytes and osteoblasts responded to serum with a two- to threefold induction of PGHS-2 mRNA. Serum stimulated PGHS-2-derived PGE 2 release from osteoblasts and osteocytes but not from periosteal fibroblasts as NS-398, a PGHS-2 blocker, inhibited PGE 2 release from osteocytes and osteoblasts with 65%, but not that from periosteal fibroblasts. On the other hand PFF (0.7 Pa, 5 Hz) stimulated (3 fold) PGHS-2 mRNA only in OCY. The related PGE 2 response could be completely inhibited by NS-398. We conclude that osteocytes have a higher intrinsic sensitivity for loading-derived fluid flow than osteoblasts or periosteal fibroblasts.