Utilization of Arachidonic and Linoleic Acids by Cultured

endothelial cells are supplemented with linoleic acid, the arachidonic acid content of the cellular phospho-lipids is reduced-35%. Most of the fatty acid com-positional change occurs during the first 24 h. One factor responsible for this effect is the inability of the endothelial cells to convert appreciable amounts of linoleic to arachidonic acid, due to a fatty acid A6-desaturase deficiency. By contrast, these endothelial cultures contain A5- and A9-desaturase activity and are able to elongate long-chain polyunsaturated fatty acids. The other factor that contributes to the decrease in arachidonic acid is that high concentrations of linoleic acid reduce the incorporation of arachidonate into cellular phospholipids. Stearic acid, a long-chain satu-rate, does not produce any reduction, whereas eico-satrienoic acid is an even more effective inhibitor than linoleic acid. In spite of the fact that high concen-trations of these polyunsaturates produced inhibition, the endothelial cells were found to efficiently in-corporate exogenous arachidonic acid into cellular phospholipids and triglycerides. This may serve to compensate for the inability of these cells to syn-thesize arachidonic acid from linoleic acid. These find-ings suggest that the endothelium obtains arachidonic acid from an extracellular source, that this cannot be provided in the form of linoleic acid and, in fact, that high concentrations of linoleic acid actually may inter-fere with the ability of the endothelium to maintain an adequate supply of intracellular arachidonic acid