Role of Platelet Α2-Adrenoreceptor in Biological Low Response to Clopidogrel for Patients with Non Cardioembolic Ischemic Stroke or Transient Ischemic Attack.

Background and purpose: Low biological response to Clopidogrel prescribed after non cardioembolic ischemic stroke or transient ischemic attack (TIA) is a major clinical problem and could explain the recurrence of vascular events. Platelet alpha 2-adrenoreceptors are involved in the high residual platelet reactivity in stable coronary artery disease patients on dual antiplatelet therapy. In the present study we investigated the impact of platelet alpha 2-adrenoreceptors on ADP-induced platelet aggregation and on ADP-induced platelet membrane CD62P (P-selectin) expression, a marker of platelet activation on blood samples from patients hospitalized at the acute phase of a non cardioembolic ischemic stroke or TIA. Methods: 72 consecutive patients were prospectively recruited over the course of two years in a monocentric study. Patients received a daily 75 mg-dose of Clopidogrel. ADP-induced platelet aggregation was measured alone, with low dose epinephrine or with atipamezole, a selective alpha blocker of alpha 2-adrenoreceptors, by Light Transmittance Aggregometry (LTA). Platelet membrane expression of P-selectin was measured by flow cytometry with either ADP alone or combined with epinephrine. Results: Epinephrine at low dose stimulated ADP-induced platelet membrane expression of CD62P whereas Atipamezole significantly inhibited 10 mu M ADP-induced platelet aggregation. Conclusions: Our study showed the role of platelet alpha 2-adrenoreceptors in biological low response to Clopidogrel for patients hospitalized for a non-cardioembolic ischemic stroke or TIA. Atipamezole could improve the status of biological response to Clopidogrel.