Proliferation-dependent Changes in Release of Arachidonic Acid

Stimulation of endothelial cells resulted in release of arachi-donic acid from phospholipids. The magnitude of this re-sponse decreased as the cells became confluent and the change coincided with a decrease in the percentage of cells in growth phases (G2 + M); this was not a consequence of time in culture or a factor in the growth medium. Precon-fluent cells released 30 % of arachidonic acid; confluent cells released only 6%. The decreasing release of arachi-donic acid was demonstrated using metabolic labeling, mass measurements of arachidonic acid, and measurement of PGI2. The decrease was not due to a changing pool of arachi-donic acid, and mass measurements showed no depletion of arachidonic acid. Release from each phospholipid and from each phospholipid class decreased with confluence. Conver-sion of confluent cells to the proliferative phenotype by me-chanical wounding of the monolayer caused increased re-lease of arachidonic acid. Potential mechanisms for these changes were investigated using assays of phospholipase ac-tivity. Phospholipase A2 activity changed in concert with the alteration in release, a consequence of changes in phosphor-ylation of the enzyme. The increased release of arachidonic acid from preconfluent, actively dividing cells may have im-portant physiologic implications and may help elucidate mechanisms regulating release of arachidonic acid. (J. Clin