ORIGINAL ARTICLE: PDF OnlyClonidine-specific antibodies as models for imidazole and α2-adrenergic receptor binding sites implications for the structure of clonidine-displacing substanceMeeley, Mary P.; Ernsberger, Paul; McCauley, Phillip M.; Reis, Donald J. Author Information From the Division of Neurobiology, Cornell University Medical College, New York, NY 10021, USA. Journal of Hypertension: December 1988 - Volume 6 - Issue 4 - p S490-493 Buy Abstract Polyclonal antisera raised against para-aminoclonidine coupled to haemocyanin exhibit high affinity for para-aminoclonidine, clonidine and chloroethylclonidine (IC50 <100 nmol/l). Anti-para-aminoclonidine antibodies also cross-react with naphazoline, oxymetazoline and tolazoline at moderate concentrations (IC50, 300–500 μmol/l); the phenyl-imidazoles detomidine, medetomidine and MPV830 are weakly cross-reactive (IC50 >0.2 mmol/l). All of these compounds bind with high affinity to both imidazole and α2-adrenergic receptors. Compounds which are imidazole- or α2-specific do not cross-react with anti-para-aminoclonidine antibodies (IC50 >1 mmol/l). Anti-para-aminoclonidine also recognizes an endogenous clonidine-displacing substance in the brain. Thus, (a) binding to anti-para-aminoclonidine antibodies defines a subset of phenyl-imidazol(in)e ligands which bind to both imidazole and α2-adrenergic receptors, suggesting that anti-para-aminoclonidine recognition sites resemble a hybrid of the two receptor types; (b) antibodies to imidazole- or α2-specific agents may be useful as models for differentiating between these types; (c) since clonidine-displacing substance is recognized by anti-para-aminoclonidine antibodies, it may have phenyl and imidazole rings as parts of its chemical structure. © Lippincott-Raven Publishers.