IN-VITRO EFFECT OF ENDOTHELIN-1 ON COLLAGEN AND ADP-INDUCED AGGREGATION IN HUMAN WHOLE-BLOOD AND PLATELET-RICH PLASMA

The effect of ET-1 on ADP- and collagen-induced platelet aggregation i n whole blood and platelet rich plasma (PRP) was studied in 39 healthy volunteers. Although ET-1 itself did not cause platelet aggregation, a marked enhancement of ADP-induced aggregation after the preincubatio n with ET-1 for 5 min was observed in whole blood, but not in PRP. Thi s ET-1 concentration and preincubation time-dependent phenomenon could be demonstrated only at threshold concentrations (5 and 7.5 mu M) of ADP and is probably due to an interaction of ET-1 with cells which are involved in the whole blood aggregation, such as polymorphonuclear ne utrophils. in whole blood and PRP an inhibition of collagen-induced ag gregation after the preincubation with ET-1 was detected. In contrast to ADP, a direct influence of ET-1 on platelet activation after the ad dition of collagen is therefore more likely. These results suggest tha t human platelets may possess ET-1 receptor(s) and that ET-1 may also interact with other blood cells.