Dexamethasone-induced stimulation of arachidonic acid release by U937 cells grown in defined medium

Since the presence of serum in culture media has been shown to alter prostaglandin production, as well as to interfere with the action of anti-inflammatory drugs, we have studied the effect of dexamethasone, a potent steroidal anti-inflammatory drug, on the metabolism of arachidonic acid by human monocyte-like cells (U937) grown in a fully defined medium. Under these culture conditions, dexamethasone (10(-6) M, 24 h) induced a marked stimulation of the release of unmetabolized arachidonic acid into the culture medium. The steroid also induced an inhibition of cell proliferation which became significant only after 48 h of treatment. The accumulation of arachidonic acid in the medium after steroid treatment was associated with a significant inhibition of cell acyltransferase activity, suggesting that steroids may also act upon arachidonic acid metabolism at sites other than those of phospholipase activity.