Inhibition of IP in human platelets diminishes 12-HETrE antiplatelet effects PAR4-mediated platelet aggregation. The minimal concentration of PAR4-AP (25-50 µM) inducing full platelet aggregation (>70%) in DMSO-treated human platelets was used to stimulate platelets incubated with increasing concentrations of 12-HETrE (5-25 µM) in the presence of a vehicle control or an antagonist to IP (R03244794; 250 nM; n = 3-6) (A), EP₂ (TG4-155; 2 μM) and EP4 (CJ-42794; 80 nM) (n = 5) (B), or DP1 (MK 0524; .4 nM; n = 5) (C). Two-way statistical analysis of variance was performed. Known antiplatelet prostanoid receptor agonists PGI₂ (4 nM), PGE₂ (20 μM), and PGD₂ (30 nM) were used to confirm the efficacy of R03244794, TG4-155/CJ-42794, or MK 052480, respectively. Two-tailed, paired t test was performed; *P < .05, **P < .01, ***P < .001. Data represent mean ± standard deviation.