Osteoblasts respond to pulsatile fluid flow with shortterm increases in PGE(2) but no change in mineralization

Although there is no consensus as to the precise nature of the mechanostimu latory signals imparted to the bone cells during remodeling, it has been po stulated that deformation-induced fluid flow plays a role in the mechanotra nsduction pathway. In vitro, osteoblasts respond to fluid shear stress with an increase in PGE(2) production; however, the long-term effects of fluid shear stress on cell proliferation and differentiation have not been examin ed. The goal of this study was to apply continuous pulsatile fluid shear st resses to osteoblasts and determine whether the initial production of PGE(2 ) is associated with long-term biochemical changes. The acute response of b one cells to a pulsatile fluid shear stress (0.6 +/- 0.5 Pa, 3.0 Hz) was ch aracterized by a transient fourfold increase in PGE(2) production. After 7 days of static culture (0 dyn/cm(2)) or low (0.06 +/- 0.05 Pa, 0.3 Hz) or h igh (0.6 +/- 0.5 Pa, 3.0 Hz) levels of pulsatile fluid shear stress, the bo ne cells responded with an 83% average increase in cell number, but no stat istical difference (P > 0.53) between the groups was observed. Alkaline pho sphatase activity per cell decreased in the static cultures but not in the low- or high-flow groups. Mineralization was also unaffected by the differe nt levels of applied shear stress. Our results indicate that short-term cha nges in PGE(2) levels caused by pulsatile fluid flow are not associated wit h long-term changes in proliferation or mineralization of bone cells.