Alpha-adrenoceptor number and function in platelets from treated and untreated patients with essential hypertension and age- and sex-matched controls.

Alpha 2-receptor number was measured on platelets from 19 healthy normotensive volunteers and 19 patients with essential hypertension, using [3H]-yohimbine binding. Platelet function was assessed using the primary aggregation response to adrenaline. The mean alpha 2-receptor number (Bmax fmol/10(8) platelets) in platelets from normotensive controls was 31 (188 sites/cell) and was significantly higher than in age- and sex-matched hypertensive subjects, for whom Bmax = 24 (144 sites/cell) (P < 0.01 by paired t-test). There was no change in the affinity for [3H]-yohimbine binding. Platelet aggregation responses to adrenaline did not differ between hypertensive and normotensive subjects. Blood pressure reduction with prazosin in eight hypertensive subjects did not alter receptor number either acutely or following 1 month of treatment. These findings may be interpreted as evidence for enhanced receptor coupling to functional responses of a significantly smaller receptor population in patients with essential hypertension.