Phenoxybenzamine is more potent in inactivating alpha 1- than alpha 2-adrenergic receptor binding sites.

The effects of phenoxybenzamine on alpha 1- and alpha 2-adrenergic receptor binding sites were examined directly using radioligand binding assays of the antagonist drugs [125I]BE 2254 and [3H]rauwolscine, respectively, in homogenates of rat cerebral cortex. Treatment with phenoxybenzamine caused an irreversible, dose-dependent decrease in the density of both alpha 1- and alpha 2-adrenergic receptors. Phenoxybenzamine was approximately 250-fold more potent at decreasing alpha 1-adrenergic receptor density than it was at decreasing alpha 2-adrenergic receptor density.