Enzymatic conversion of prostaglandin endoperoxide H2 and arachidonic acid to prostacyclin by cultured human endothelial cells.

SUMMARY Synthesis of prostacyclin, as measured by its stable end product, 6-keto-prostaglandin (PG) FI,, was studied in resting endothelial cell monolayers. When [l-14C]ar- achidonate (20 PM, 0.4 PCi) was incubated with cultured human endothelial cells for 20 min, prostacyclin ap- peared in the supernatant along with small amounts of prostaglandins Fza and Ez. Pretreatment of the culture system with acetylsalicylic acid (100 PM) or 15-hydro- peroxyarachidonic acid abolished prostacyclin synthe- sis. Unlike the supernatants, the cells themselves did not contain measurable prostaglandins after arachi- donic acid incubation. Cell-associated radioactivity was only present in the phospholipid fraction and in a peak representing unconverted arachidonate. Omis- sion of cells from the culture system resulted in no conversion of arachidonic acid. Endothelial cell monolayers were pretreated with acetylsalicylic acid in order to block endogenous pros- taglandin synthesis and then incubated for 5 min with [1-‘4C]PGHz (2