Stimulation of Endothelial Cell Prostacyclin Production by Thrombin, Trypsin, and the Ionophore A 23187

TLDR

Prostacyclin (PGI₂) is a short‑lived prostaglandin that blocks platelet aggregation, suppresses serotonin release, and induces vasodilation. The authors quantified PGI₂ activity by measuring the ability of endothelial or fibroblast supernatants to inhibit platelet aggregation or thrombin‑induced serotonin release in platelet‑rich plasma. Endothelial monolayers released PGI₂ in response to arachidonate, thrombin, trypsin, or the ionophore A 23187, whereas fibroblasts responded only to arachidonate; PGI₂ production was absent in resting cells, abolished by indomethacin, tranylcypromine, or 15‑hydroperoxy arachidonic acid, destroyed by heat or acid, and prevented by inhibiting thrombin or trypsin, suggesting that thrombin‑induced PGI₂ synthesis could temper platelet recruitment at vascular injury.

Abstract

Prostacyclin (PGI2) is an unstable prostaglandin which inhibits platelet aggregation and serotonin release and causes vasodilation. The PGI2 activity produced by monolayers of cultured human endothelial cells and fibroblasts was measured by the ability of their supernates to inhibit platelet aggregation in platelet-rich plasma, or to inhibit thrombin-induced [14C]serotonin release from aspirin-treated, washed platelet suspensions. Monolayers of cultured human endothelial cells, stimulated with sodium arachidonate, thrombin, the ionophore A 23187, or trypsin, secreted PGI2 into the supernatant medium. Monolayers of fibroblasts produced PGI2 activity only when stimulated by arachidonate. “Resting,” intact monolayers did not produce detectable PGI2, nor did monolayers treated with ADP or epinephrine. Production of PGI2 activity was abolished by treatment of the monolayers with indomethacin, tranylcypromine, or 15-hydroperoxy arachidonic acid. The PGI2 activity of the supernates was destroyed by boiling or acidification. Inhibition of thrombin with diisopropylfluoro-phosphate, and of trypsin with soybean trypsin inhibitor, abolished the stimulation of PGI2 production by these enzymes. Production of thrombin at a site of vascular injury could, by stimulating PGI2 synthesis by endothelial cells adjacent to the injured area, limit the number of platelets involved in the primary hemostatic response and help to localize thrombus formation.