Prostaglandin E2Differentially Modulates Human Platelet Function through the Prostanoid EP2 and EP3 Receptors (original) (raw)

Activated human platelets synthesize prostaglandin (PG) E 2 , although at lower rate than thromboxane A 2. PGE 2 acts through different receptors (EP1-4), but its role in human platelet function remains poorly characterized as compared to thromboxane. We studied the effect of PGE 2 and its analogs on in vitro human platelet function, and platelet and megakaryocyte EP expression. Platelets pre-incubated with PGE 2 or its analogs were stimulated with agonists and studied by optical aggregometry. Intraplatelet calcium mobilization was investigated by the stopped flow method, platelet vasodilator-stimulated phosphoprotein (VASP), P-selectin and microaggregates were investigated by flow cytometry. PGE 2 at nM concentrations dose-dependently increased the slope (velocity) of the secondary phase of ADP-induced platelet aggregation (EC 50 : 25.6±6 nM, Emax of 100±19% increase vs. vehicle-treated), without affecting final maximal aggregation. PGE 2 stabilized reversible aggregation induced by low ADP concentrations (EC 50 37.7±9 nM). The EP3 agonists, 11-deoxy-16,16-dimetyl PGE 2 (11d-16dm PGE 2) and sulprostone enhanced the secondary wave of ADP-induced aggregation, with EC 50 of 48.6±10 nM (Emax 252±51%) and 5±2 nM (Emax 300±35%), respectively. The EP2 agonist butaprost inhibited ADP-induced secondary phase slopes (IC 50 40±20 nM). EP4 stimulation had minor inhibitory effects. 11d-16dm PGE 2 alone raised intraplatelet Ca 2+ and enhanced ADP-induced Ca 2+ increase. 11d-16dm PGE 2 and 17-phenyl-trinor PGE 2 (EP3>EP1 agonist) at nM concentrations counteracted PGE 1-induced VASP phosphorylation, induced platelet microaggregates, and P-selectin expression. EP1, EP2, EP3 and EP4 were expressed on human platelets and megakaryocytes.PGE 2 through different EPs finely modulates human platelet responsiveness. These findings should inform the rational selection of novel antithrombotic strategies based on EP modulation.