Platelet α2-adrenoceptor alterations in patients with essential hypertension are normalized after treatment with doxazosin but not propranolol

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Abstract
Marked alterations have been demonstrated to occur in the platelet alpha2-adrenoceptors of patients with essential hypertension. The purpose of this study was to determine whether antihypertensive treatment with alpha-adrenergic blocker doxazosin or beta-adrenergic blocker propranolol can affect the affinity and the density of platelet alpha2-adrenoceptors in such patients. In two groups of 22 previously untreated, essential hypertensive patients, the mean affinity (Kd) and density (B(max)) of platelet alpha2-adrenoceptors were studied by [3H]-UK 14304 binding assays; the first assays were performed before any medication was begun, the second were performed after treatment for up to 13 weeks with doxazosin or propranolol. A third group of 22 healthy normotensive volunteers matched by age, sex and body mass index was used as control. Blood pressure did not differ significantly in the two hypertensive groups, and treatment with the two drugs resulted in closely similar, normal blood pressure levels. Kd and B(max) values were significantly higher in the two hypertensive groups than in controls. After treatment with propranolol the binding parameters did not change significantly, whereas after treatment with doxazosin Kd and B(max) returned to normotensive values. In previously untreated, essential hypertensive patients platelet alpha2-adrenoceptors have a lower affinity but a higher density than in normotensive subjects. Despite similar effects on blood pressure, the treatment with the alpha-adrenergic blocker doxazosin is followed by restoration of normal findings in the binding assays of platelet alpha2-adrenoceptors whereas the treatment with the beta-adrenergic blocker propranolol does not alter the Kd and B(max) values.