Verapamil interacts in vitro with alpha 2-adrenoceptors but does not modify alpha 2-receptivity in vivo.

The kind of interaction of two structurally different calcium channel blockers (verapamil and nicardipine) with both α 2 -adrenergic agonist and antagonist binding on human platelets was investigated. Only verapamil, but not nicardipine, interacted in vitro with platelet α 2 -adrenoceptors on [ 3 H]-yohimbine or [ 3 H]-UK 14,304 binding. Verapamil (120 mg t.i.d. orally during 1 month) failed to modify the platelet α 2 -adrenoceptor number or the adrenaline-induced platelet aggregation in hypertensive patients