Effect of Ro 31-8220 or receptor-selective antagonists on PAR1- and PAR4-induced inhibition of adenylyl cyclase in normal human platelets.

Effect of PAR1 and PAR4 agonists on platelet adenylyl cyclase was determined as described in “Materials and methods.” Data are expressed as percentage of total [³H]cAMP. The data are normalized to the level of cAMP in response to 10 μM PGE₁ (taken as 100%) or to the level of PGE₁-stimulated cAMP in the presence of 10 μM Ro 31-8220. Ro 31-8220 or dimethyl sulfoxide (control) was added to aspirin-treated platelets and incubated for 5 minutes at 37°C with stirring before the addition of either PGE₁ alone or PGE₁ with agonists; 1 μM AR-C66096 was added 30 seconds prior to agonists, SFLLRN (10 μM) or GYPGKF (700 μM). Each data point is the mean ± SE of at least 3 experiments.