The adrenalin binding site on human platelets.
Using 3H-adrenalin the quantity and characteristics of the adrenalin receptors on human platelets were evaluated. Maximum adrenalin binding by intact platelets from eight normal subjects averaged 3.2 ng adrenalin/10(8) platelets, equivalent to 105 000 binding sites per platelet. Bound 3H-adrenalin could be dissociated or binding could be inhibited by an excess of unlabelled adrenalin, noradrenalin, isoproterenol or dopamine; phentolamine or propanalol had no effect on 3h-adrenalin binding, even in concentrations 10 000-fold greater. These studies show that the epinephrine binding site can be detected and quantitiated on human platelets and that its characteristics differ from those classically attributed to either alpha or beta adrenergic receptors.