Flow cytometric analysis of platelet activation in hypertensive patients.: Effect of doxazosin

The percentage of spontaneously activated platelets and the platelet response to several agonists were studied in 26 hypertensive patients. The percentage of platelets expressing glycoprotein (GP) IIb/IIIa in its active conformation (GPIIb/IIIa*), P-selectin and phosphatidylserine (PS) was measured by flow cytometry at baseline and I and 2 months after treatment with doxazosin (4 mg/day). The response to ADP and Ca2+ ionophore was also evaluated. The results were compared with those of a control group of 71 normotensive volunteers. Spontaneous platelet activation was higher in patients than in controls (P-selectin-positive results in 4.4 +/- 2.0% patients vs. 2.7 +/- 1.7 controls, p < 0.05; phosphatidylserine-positive results in 0.7 +/- 0.4% vs. 0.5 +/- 0.3%, respectively, p < 0.05), and higher in response to ionophore action (phosphatidylserine-positive results 51.8 +/- 11.1 % vs. 43.4 +/- 11.7%, p < 0.01). Platelet activation in patients decreased after 2 months of doxazosin administration compared to baseline (P-selectin-positive results 2.7 +/- 1.4% vs. 4.4 +/- 2.0%, p < 0.05; phosphatidylserine-positive results 0.3 +/- 0.2% vs. 0.7 +/- 0.4%, p < 0.05). No significant differences were noted in GPIIb/IIIa*. The clinical significance of normalization of platelet activity by doxazosin remains to be established. (C) 2003 Elsevier Ltd. All rights reserved.