Immediate responses of endothelial cells to hypoxia and reoxygenation: An in vitro model of cellular dysfunction

We have studied endothelial functions and integrity under clinically relevant levels of acute and profound hypoxia. Bovine aortic endothelial cells (EC) grown on micro-carrier beads were exposed for 15-min intervals to normoxic (20% O₂) or hypoxic (1-2% O₂) medium. Control intervals were followed by four hypoxic and then four normoxic intervals for reoxygenation. Prostacyclin release from EC significantly decreased after only 15 min of hypoxia and remained low despite reoxygenation. This decrease in prostacyclin release was not coincident with decreased viable cells (Trypan blue exclusion) or with increased cell lysis (increased lactate dehydrogenase) after hypoxia or reoxygenation. When the medium was supplemented with 30 μM arachidonate (saturating concentration), prostacyclin release still significantly decreased after 30 min of hypoxia but returned to baseline levels by 30 min of reoxygenation. Similar results were obtained for thromboxane B₂ release. These data suggest that 1) EC decrease prostacyclin release during acute, profound hypoxia, 2) EC decrease prostaglandin production during hypoxia despite abundant exogenous arachidonate, and 3) recovery of prostaglandin production is dependent on exogenous arachidonate during reoxygenation.