title: An affinity label for alpha 2-adrenergic receptors in rat brain.
abstract: Clonidine, a potent and highly selective alpha 2-adrenergic agonist of the central nervous system, was modified. Insertion of the strong alkylating isothiocyanate group (NCS) group, at its aromatic residue, makes clonidine a potential affinity label of the alpha 2-adrenergic receptors. In displacement of [3H]clonidine and p-[3H]aminoclonidine from rat brain membrane preparations, clonidine-NCS demonstrates high affinity for the alpha 2-adrenergic receptors (Kd = 50 mM). The covalent labelling of the central alpha 2-receptors requires higher concentrations of the irreversible ligand (1-70 microM), thus indicating possible non-productive interactions at the environment of the receptor site. Only partial protection of the receptors is observed with a reversible alpha 2-agonist. The new clonidine analog appears to be a general ligand for the alpha 2-adrenergic receptors and might serve as a potential affinity probe for these receptors.
mesh_terms: D000345:Affinity Labels / Q000138:chemical synthesis*; D000818:Animals; D001667:Binding, Competitive; D001923:Brain Chemistry; D002462:Cell Membrane / Q000378:metabolism; D003000:Clonidine / Q000031:analogs & derivatives* / Q000138:chemical synthesis / Q000378:metabolism; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D011941:Receptors, Adrenergic / Q000032:analysis*; D011942:Receptors, Adrenergic, alpha / Q000032:analysis*
chemical_list: D000345:Affinity Labels; D011941:Receptors, Adrenergic; D011942:Receptors, Adrenergic, alpha; C034199:clonidine 4-isothiocyanate; C016986:apraclonidine; D003000:Clonidine