Endothelial cells derived from human umbilical veins represent an established model for endothelial cell research. However, it may be possible that endothelial cell physiology shows topographic differences. Until now, our research concentrated on an ovine ischemia/reperfusion model. Sheep subjected to 3 h of infrarenal aortic clamping followed by 4 h of reperfusion developed secondary lung damage. This damage is related to an infiltration of polymorphonuclear granulocytes into the lung tissue in accordance with an increased pulmonary permeability. To study this phenomenon in vitro, endothelial cells of ovine pulmonary arteries were cultured onto Transwell-membranes. The permeability of a monolayer of the endothelial cells was tested after stimulation with PMA, TNF-α, serum of experimental sheep, and serum of control sheep. Different sizes (4, 20, and 70 kDa) of dextran molecules conjugated to FITC were applicated at the top of the monolayer. After 5 h of incubation, fluorescence activity of both the upper and lower chamber was measured. PMA stimulation lead to a permeability of over 80%. Serum of experimental sheep increased permeability with 21.3% (mean of all dextrans). This increase was partially mediated by TNF-α (mean increase in permeability 15.4%). Thus, ischemia-reperfusion injury evokes high levels of cytokines. These cytokines may cause a remote increase in pulmonary endothelial permeability, leading to acute respiratory distress syndrome (ARDS) or organ failure.