Effects of endothelin-1 on aggregation of normal and uremic platelets

Platelet aggregation was studied in the whole blood and platelet rich plasma (PRP) upon stimulation with various agonists (collagen- 0.5 microgram/ml in the whole blood and PRP, ADP 10 microM in the whole blood and 2 microM in PRP, ristocetin 0.75 mg/ml in the whole blood and 1.25 mg/ml in PRP and arachidonic acid (AA) 0.5 mM in the whole blood and PRP) following incubation with ET-1 at final concentrations of 0.1 microM and 0.2 microM for 1 and 5 min. Collagen- and ADP-induced platelet aggregation in PRP was found to be diminished following incubation with ET-1 for 1 and 5 min at the concentrations of 0.1 microM and 0.2 microM. Aggregation of platelets upon stimulation with AA and ristocetin remained unaltered following incubation with ET-1. In the whole blood ristocetin-induced platelet aggregation was significantly diminished following incubation with ET-1 for 5 min, whereas AA-induced platelet aggregation was not significantly changed following preincubation with ET-1. Our results suggest that platelets may possess ET-1 receptor(s) and that ET-1 may also interact with other blood cells.