LPA synergizes with ADP, epinephrine, and serotonin in inducing aggregation of washed platelets: different effects of ADP receptor antagonists. Washed human platelets were stimulated with 1-acyl-LPA (16:0) and ADP (A); 1-acyl-LPA (16:0) and epinephrine (ADR) (B); and 1-acyl-LPA (16:0) and serotonin (5-HT) (C) alone or in combination. The synergistic aggregation induced by LPA plus serotonin, but not LPA plus epinephrine was inhibited by MRS2179 or AR-C69931MX.