Alpha- and Beta-Adrenoceptors in Circulating Blood Cells of Essential Hypertensive Patients: Increased Receptor Density and Responsiveness

Abstract

In 40 male patients with established essential hypertension (Pdiast > 95 mmHg) platelet α₂-adrenoceptor density (by ³H-yohimbine binding) and -responsiveness (by adrenaline-induced aggregation) as well as lymphocyte β2-adrenoceptor density (by (±)-¹²⁵ iodocyanopindolol binding) and -responsiveness (by cyclic AMP responses to isoprenaline) were determined and compared with those in 40 male age-matched normotensives (Pdiast < 90 mmHg). In essential hypertensive patients mean platelet α2- and lymphocyte β2-adrenoceptor densities were significantly increased. When data from all 80 subjects were combimed, significant positive correlations between mean arterial blood pressure and α2-and β2-adrenoceptor densities, respectively, were found. The increases in α2-and β2-adrenoceptor densities were accompanied by enhanced responsiveness to adrenergic stimulation: in platelets adrenaline-induced aggregation—via α2-adre-noceptor stimulation—was exaggerated, and in lymphocytes isoprenal ine produced significantly greater increases in the intracellular level of cyclic AMP. It is concluded that the increased density and responsiveness of α2-and β2-adrenoceptors in circulating blood cells of essential hypertensive patients may reflect increased sympathetic activity, which might contribute to the elevation of blood pressure.

Key Words:

• α-adrenoceptors
• β-adrenoceptors
• sympathetic activity
• essential hypertension