Arachidonic acid release from cultured human amnion cells: the effect of dexamethasone.

Glucocorticoids inhibit prostaglandin (PG) synthesis in several cell types, presumably by inhibiting arachidonic acid (AA) deacylation from phospholipids. We studied the effects of glucocorticoids on cultured term human amnion cell AA release. Confluent monolayer cultures of amnion cells were adapted to serum-free medium, and phospholipids were labeled for 18 h with [14C]AA. The calcium ionophore A23187 (0.2-5.0 mumol/L) stimulated [14C]AA release (up to 2.2-fold) in a dose- and time-dependent manner. The apparent sources of the liberated [14C]AA were phosphatidylcholine and phosphatidylethanolamine. Pretreatment for 24 h with the synthetic glucocorticoid dexamethasone (0.1-1000 nmol/L) significantly inhibited (P less than 0.01) basal (unstimulated) [14C]AA release by 69% in subsequent 1-h experiments. The sole apparent source of free [14C]AA during this inhibitory state was phosphatidylethanolamine. Dexamethasone pretreatment slightly inhibited (13%; P less than 0.05) calcium ionophore-stimulated [14C]AA release; however, it was still 3.8-fold greater than basal release, suggesting that the glucocorticoid effect on stimulated AA release was not biologically relevant. Further characterization of the glucocorticoid effect revealed that preincubation of the cultures with dexamethasone for as little as 20 min inhibited basal [14C]AA release. Furthermore, studies involving actinomycin-D and cycloheximide demonstrated that inhibition of RNA and protein synthesis failed to block the glucocorticoid inhibition of basal AA liberation. The glucocorticoid receptor antagonist RU 38486, alone or in the presence of dexamethasone, also inhibited unstimulated [14C]AA release. Cortisol, dehydroisoandrosterone sulfate, 17 beta-estradiol, and progesterone all inhibited basal [14C]AA liberation. We conclude that glucocorticoids inhibit unstimulated AA release from cultured amnion cells, but do not prevent calcium ionophore from stimulating a large increase in AA release.(ABSTRACT TRUNCATED AT 250 WORDS)