Effects of oxygen tension and shear stress on human endothelial cell prostacyclin production

Under in vivo conditions of ischemia and reperfusion, vascular endothelium (EC) experience concurrent changes in oxygen tension, shear stress, and the local concentration of metabolites. These studies explored the combined effects of shear stress and oxygen tension on EC prostacyclin production. EC grown on microcarrier beads were exposed to 120 min of normoxia and basal shear stress by stirring at 20 rpm. After normoxia, EC were exposed to hypoxia (2% O₂, 20 rpm), ischemia (2% O₂, 5 rpm) or sham ischemia (20% O₂, 5 rpm). Following hypoxia, EC were reoxygenated (20% O₂, 20 rpm). After ischemia and sham ischemia, EC were reperfused (20% O₂, 20 rpm). Minimal accumulation of metabolites occurred during normoxia, hypoxia, and reperfusion. All metabolites were allowed to accumulate in the flasks during ischemia and sham ischemia. Prostacyclin levels were measured by ELISA, and prostaglandin H₂ synthase levels in cells were analyzed by immunoblotting. An acute decrease in shear stress decreased prostacyclin production. An acute decrease only in oxygen tension did not alter prostacyclin production significantly. The combined acute decrease in both shear stress and oxygen tension significantly stimulated prostacyclin production for 30 min. By 120 min of ischemia and hypoxia, prostacyclin release was significantly less than sham ischemia. Prostacyclin production after 30 min of reoxygenation was significantly less than that of cells subjected to reperfusion. By 120 min of reperfusion and reoxygenation, there was no significant difference in EC prostacyclin synthesis. These findings suggest that temporal and quantitative aspects of EC prostaglandin synthesis are dependent on both oxygen tension and shear stress.