[3H]RX 781094: a new antagonist ligand labels alpha 2-adrenoceptors in the rat brain cortex.
[3H]RX 781094 [(imidazolinyl-2)-2 benzodioxane-1,4 [3H]chlorhydrate], a specific alpha 2-adrenoceptor antagonist radioligand, has been used to characterize alpha 2-adrenoceptors in rat cortical membranes. [3H]RX 781094 binding is reversible, saturable and stereospecific. It labels with high affinity a single population of non-interacting sites. The KD value was 3.9 +/- 0.4 nM and the Bmax 189.0 +/- 12.4 fmol/mg protein. Competition curves with different alpha-adrenoceptor agonists and antagonists showed that the binding sites labelled with [3H]RX 781094 had the pharmacological characteristics of alpha 2-adrenoceptors. Pretreatment with reserpine (2.5 mg/kg s.c., 24 h before the experiment) did not affect the KD or Bmax values of [3H]RX 781094 binding. Chemical destruction of noradrenergic pathways by systemic injection of DSP4 or intracerebral injection of 6-hydroxydopamine did not modify the KD or the Bmax of [3H]RX 781094 binding. It is concluded that the major proportion of alpha 2-adrenoceptors labelled with [3H]RX 781094 are not localised to noradrenergic nerve terminals.
D000317:Adrenergic alpha-Antagonists; D000818:Animals; D001596:Benzylamines / Q000494:pharmacology; D001667:Binding, Competitive; D002540:Cerebral Cortex / Q000378:metabolism*; D004147:Dioxins; D006892:Hydroxydopamines / Q000494:pharmacology; D019329:Idazoxan; D008297:Male; D016627:Oxidopamine; D051381:Rats; D011919:Rats, Inbred Strains; D011942:Receptors, Adrenergic, alpha / Q000032:analysis*; D012110:Reserpine / Q000494:pharmacology
D000317:Adrenergic alpha-Antagonists; D001596:Benzylamines; D004147:Dioxins; D006892:Hydroxydopamines; D011942:Receptors, Adrenergic, alpha; D012110:Reserpine; D016627:Oxidopamine; C012102:DSP 4; D019329:Idazoxan