Blockade of adenosine diphosphate receptors P2Y(12) and P2Y(1) is requiredto inhibit platelet aggregation in whole blood under flow

Using heparinized whole blood and flow conditions, it was shown that adenos ine 5'-diphosphate (ADP) receptors P2Y(12) and P2Y(1) are both important in direct shear-induced platelet aggregation and platelet aggregation subsequ ent to initial adhesion onto von Willebrand factor (vWf)-collagen. In the v iscometer, whole blood was subjected to shear rates of 750, 1500, and 3000 s(-1) for 30 seconds at room temperature. The extent of aggregation was det ermined by flow cytometry. The P2Y(12) antagonist AR-C69 931MX (ARMX) reduc ed shear-induced aggregation at these rates by 56%, 54%, and 16%, respectiv ely, compared to control samples. Adenosine 3',5'-diphosphate (A3P5P; P2Y(1 ) antagonist) inhibited shear-induced aggregation by 40%, 30% and 29%, resp ectively, compared to control samples. Blockade of both ADP receptors at 30 00 s(-1) with ARMX plus A3P5P further reduced the platelet aggregation by 4 1% compared to the addition of ARMX alone (57% compared to control samples) . Using a parallel-plate flow chamber, whole blood was perfused over bovine collagen type 1 at a wall shear rate of 3000 s(-1) for 60 seconds. Platele t deposition was quantified with epifluorescence video microscopy and digit al image processing. Blockade of P2Y(12) alone or blockade of P2Y(1) alone did not reduce thrombus formation on vWf-collagen. In contrast, blockade of both P2Y(12) and P2Y(1) reduced platelet deposition by 72%. These results indicate that combinations of antagonists of the ADP receptors P2Y(12) and P2Y(1) are effective inhibitors of direct shear-induced platelet aggregatio n and of platelet aggregation subsequent to initial adhesion under flow con ditions. Inhibitors of these pathways are potentially useful as antiarteria l thrombotic agents. (Blood. 2001;98: 3340-3345) (C) 2001 by The American S ociety of Hematology.