Increased density and responsiveness of alpha 2 and beta-adrenoceptors in circulating blood cells of essential hypertensive patients

Abstract

In 40 male patients with established essential hypertension (P diastolic greater than mmHg) the density and responsiveness of platelet alpha 2-adrenoceptors and lymphocyte beta 2-adrenoceptors were measured and compared with those in 40 male age-matched normotensive subjects (P diastolic less than 90 mmHg). The mean densities of platelet alpha 2-adrenoceptors (assessed by 3H-yohimbine binding) and of lymphocyte beta 2-adrenoceptors (assessed by (+/-) 125 iodocyanopindolol binding) were significantly increased in essential hypertensive patients (P less than 0.01). If data from all 80 subjects were combined there were significant positive correlations between mean arterial blood pressure of the subjects and alpha 2-adrenoceptor density (r = 0.591, P less than 0.001) and beta 2-adrenoceptor density (r = 0.648, P less than 0.001), respectively. The increases in and beta-adrenoceptor densities in essential hypertension were accompanied by enhanced responsiveness alpha- of platelets to 10 microM adrenaline to adrenergic stimulation: the aggregatory response via alpha 2-adrenoceptor stimulation) was increased, and in lymphocytes isoprenaline (0.01 - 100 microM) produced (via adrenoceptor stimulation) greater increases in cyclic AMP at each concentration than in control. Furthermore, activation of platelet adenylate cyclase by prostaglandin E1 was exaggerated in essential hypertensive patients. It is concluded that the increased density and responsiveness of alpha- and beta-adrenoceptors in essential hypertension may reflect enhanced sympathetic activity, and may contribute to the elevation of blood pressure.