Cyclooxygenase (COX)-2 is among the endothelial genes upregulated by uniform laminar shear stress (LSS), characteristically associated with atherosclerotic lesion-protected areas. We have addressed whether the induction of COX-2–dependent prostanoids in endothelial cells by LSS plays a role in restraining endothelial tumor necrosis factor (TNF)- generation, a proatherogenic cytokine, through the induction of heme oxygenase-1 (HO)-1, an antioxidant enzyme. In human umbilical vein endothelial cells (HUVECs) exposed to steady LSS of 10 dyn/cm² for 6 hours, COX-2 protein was significantly induced, whereas COX-1 and the downstream synthases were not significantly modulated. This was associated with significant (P<0.05) increase of 6-keto-prostaglandin (PG)F₁ (the hydrolysis product of prostacyclin), PGE₂, and PGD₂. In contrast, TNF- released in the medium in 6 hours (3633±882 pg) or detected in cells lysates (1091±270 pg) was significantly (P<0.05) reduced versus static condition (9100±2158 and 2208±300 pg, respectively). Coincident induction of HO-1 was detected. The finding that LSS-dependent reduction of TNF- generation and HO-1 induction were abrogated by the selective inhibitor of COX-2 NS-398, the nonselective COX inhibitor aspirin, or the specific prostacyclin receptor (IP) antagonist RO3244794 illuminates the central role played by LSS-induced COX-2–dependent prostacyclin in restraining endothelial inflammation. Carbacyclin, an agonist of IP, induced HO-1. Similarly to inhibition of prostacyclin biosynthesis or activity, the novel imidazole-based HO-1 inhibitor QC15 reversed TNF- reduction by LSS. These findings suggest that inhibition of COX-2–dependent prostacyclin might contribute to acceleration of atherogenesis in patients taking traditional nonsteroidal antiinflammatory drugs (NSAIDs) and NSAIDs selective for COX-2 through downregulation of HO-1, which halts TNF- generation in human endothelial cells.