GLUCOCORTICOID MODULATION OF PROSTACYCLIN PRODUCTION IN CULTURED BOVINE PULMONARY ENDOTHELIAL-CELLS

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Abstract
The ability of glucocorticoids to modify the production of prostacyclin by endothelial cells derived from bovine pulmonary arteries was examined. Binding studies with [3H]dexamethasone indicated that these cells possessed high-affinity binding sites for glucocorticoids (Kd .apprx. 4 nM). The cells released prostacyclin, measured serologically as its hydrolysis product 6-keto-prostaglandin F1.alpha.. The release was strongly stimulated by a 5-min incubation with 50 nM bradykinin, 2 .mu.M Ca ionophore A23187 or 1-5 .mu.M arachidonic acid. Dexamethasone, 1-20 nM, suppressed prostacyclin release in response to bradykinin and ionophore in a dose-dependent manner. The suppressive effects required 24 h for full expression. Maximal inhibition of bradykinin-induced prostacyclin release was .apprx. 65% and that of ionophore-induced release was .apprx. 35%. Total inhibition was not observed. Hydrocortisone at 20 nM inhibited bradykinin-induced release of prostacyclin by .apprx. 45% but had no effect on ionophore-induced release. Neither glucocorticoid inhibited prostacyclin release in response to arachidonic acid. Triton X-100 extracts and conditioned media from cells treated with 20 nM dexamethasone failed to modify prostacyclin release when added to fresh endothelial cells. Dexamethasone, in concentrations likely to produce virtually complete binding site occupancy, inhibits agonist-induced release of prostacyclin from bovine pulmonary endothelial cells. Inhibition appears to occur at the level of intracellular arachidonic acid release. However, definitive evidence for the production of a macromolecular phospholipase inhibitor by endothelial cells in response to these low concentrations of steriod was not obtained.

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