Neuroleptic drug interactions with norepinephrine alpha receptor binding sites in rat brain

Alpha adrenergic receptor sites in mammalian brain tissue can be labeled by the binding of [³H]WB-4101 (2-([2′,6′-dimethoxy] phenoxyethylamino) methyl benzodioxan), a potent α-adrenergic antagonist. Numerous neuroleptic drugs of phenothiazine, butyrophenone and thioxanthene classes are potent in competing for [³H]WB-4101 binding, with affinities resembling those of classic α-antagonists such as phentolamine and phenoxybenzamine. The potencies of neuroleptics in competing for WB-4101 binding sites correlate closely with their potencies in antagonizing norepinephrine and epinephrine induced lethality in rats, confirming that affinity for WB-4101 binding sites predicts α-receptor antagonism in vivo. The relative affinities of neuroleptics for WB-4101 binding sites and for dopamine receptors as labeled by [³H]haloperidol provides an index of the relative propensities of these drugs for eliciting autonomic side effects such as orthostatic hypotension and sedation.