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Marked alterations have been demonstrated to occur in the platelet α2-adrenoceptors of patients with essential hypertension. The purpose of this study was to determine whether antihypertensive treatment with α-adrenergic blocker doxazosin or β-adrenergic blocker propranolol can affect the af(r)nity and the density of platelet α2-adrenoceptors in such patients.In two groups of 22 previously untreated, essential hypertensive patients, the mean affinity (Kd) and density (Bmax) of platelet α2-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 Bmax 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 Bmax returned to normotensive values.In previously untreated, essential hypertensive patients platelet α2-adrenoceptors have a lower affinity but a higher density than in normotensive subjects. Despite similar effects on blood pressure, the treatment with the α2-adrenergic blocker doxazosin is followed by restoration of normal findings in the binding assays of platelet α2-adrenoceptors whereas the treatment with the β-adrenergic blocker propranolol does not alter the Kd and Bmax values.