Selective Blockade of P2Y12 Receptors by Prasugrel Inhibits Myocardial Infarction Induced by Thrombotic Coronary Artery Occlusion in Rats

We evaluated the effects of prasugrel, a third-generation thienopyridyl prodrug, on P2Y(12) receptors, adenosine 5'-diphosphate (ADP)-induced platelet aggregation, and myocardial infarction (MI) in rats. Oral administration of prasugrel (0.3-3 mg/kg) resulted in the dose-related inhibition of washed platelet aggregation induced by ADP (1-10 mu M). Ex vivo [H-3]-2-MeS-ADP binding to platelet P2Y(12) receptors was also inhibited by prasugrel in a similar dose range. The antiaggregatory effects of prasugrel correlated strongly with P2Y(12) blockade with correlation coefficients of 0.85-0.92, suggesting that the antiaggregatory activity of prasugrel largely reflected P2Y(12) blockade achieved in vivo. We further examined the effects of the in vivo P2Y(12) inhibition by prasugrel (1-10 mg/kg, po) on MI induced by thrombotic coronary artery occlusion in rats. In surviving rats, infarct size at 24 hours after photoirradiation was evaluated. In the vehicle group, necrosis area/total left ventricular area was 37.9% +/- 6.8% (mean +/- SE, n = 7). At all prasugrel doses tested (n = 7 for each dose), necrosis area/total left ventricular area was significantly smaller than that in the vehicle group: 14.4% +/- 4.0% for 1 mg/kg (P < 0.01), 19.8% +/- 4.5% for 3 mg/kg (P < 0.05), and 14.8% +/- 3.6% for 10 mg/kg (P, 0.01). At the highest administered dose of prasugrel (10 mg/kg), blood pressure and heart rate were unchanged. Arrhythmia was observed in 5 of 7 animals in the vehicle group at 24 hours after irradiation; in contrast, no arrhythmia was found in the group treated with prasugrel (10 mg/kg). Taken together, these results demonstrate that prasugrel is a selective P2Y(12) inhibitor in vivo, providing effective inhibition of platelet aggregation and MI in rats.