Influence of growth oxygen level on eicosanoid release from lung endothelial cells during hypoxia

Eicosanoid products of arachidonic acid are suspected modulators of hypoxic vasoconstriction in the pulmonary vasculature. Vascular endothelial cells (EC) release several eicosanoids, but there is disagreement regarding the effect of hypoxia on EC eicosanoid release. We postulated that the oxygen level of growth in culture might influence the release of eicosanoids during acute hypoxia. We studied EC cultured from the main pulmonary arteries of pigs and grown at either 5% or near 20% oxygen, representing the normal limits of oxygen exposure to endothelium in normal lungs. Although cultures grown in 5% oxygen grew slightly faster by 4 days, the confluent cell number, protein content, and baseline eicosanoid release were no different compared with paired cultures grown in 20% oxygen. However, with an acute decrease in oxygen level, cultures grown in 5% oxygen released less prostaglandin E₂, F(2α), and 6-ketoprostaglandin F(1α) compared with amounts released at the growth oxygen level. In contrast, cultures grown in 20% oxygen released increased amounts of these eicosanoids compared with release at the growth oxygen level. Release of thromboxane B₂ was not significantly different during hypoxia between cultures grown at 5% vs. 20% oxygen. In other experiments, cyclooxygenase activity, stimulated arachidonic acid release by calcium ionophore A23187, and uptake of arachidonic acid were no different in cultures grown at 5% vs. 20% oxygen. However, arachidonic acid release during hypoxia was reduced in 5% cultures and increased in 20% cultures. These experiments show that both the growth oxygen level and an acute change in oxygen level influence release of eicosanoids from pulmonary vascular EC and suggest that in vivo release of eicosanoids during hypoxia may be influenced by the oxygen level to which the cells are chronically accustomed.