Characteristics of [3H]E-643-binding to alpha adrenoceptors.

Radiolabeled E-643, a newly developed antihypertensive compound, bound specifically to a preparation obtained from rat brain with a maximum of 85 f moles of binding sites per mg protein and a dissociation constant of 0.59 nM. Prazosin markedly inhibited the binding. While yohimbine and clonidine were only weak inhibitors. Other characteristics of the binding of [3H]E-643 to the brain and its specific binding to preparations of peripheral rat organs were also studied. The present findings suggest that [3H]E-643 is useful for labeling alpha 1-adrenoceptors.