Clonidine-specific antisera recognize an endogenous clonidine-displacing substance in brain

Area of Science:

• Neuroscience
• Pharmacology
• Immunology

Background:

• Clonidine-displacing substance is an endogenous brain compound with biological activity.
• It binds to the same receptor populations as clonidine.
• Antiligand antibodies can model receptor binding sites.

Purpose of the Study:

• To test the hypothesis that antibodies against a clonidine analog recognize structurally related compounds, including clonidine-displacing substance.
• To characterize the structural determinants recognized by these antibodies.

Main Methods:

• Polyclonal antibodies were raised against p-aminoclonidine coupled to hemocyanin.
• Competitive radioimmunoassay using tritiated p-aminoclonidine as the radioligand was employed.
• Immunoprecipitation experiments were conducted.

Main Results:

• Central vasodepressor agents containing imidazol(in)e and phenyl rings inhibited radioligand binding.
• Compounds lacking these rings did not cross-react.
• Partially purified bovine clonidine-displacing substance inhibited binding in a dose-dependent manner (IC50, 4 Units).
• Immunoprecipitation confirmed antibody recognition of clonidine-displacing substance.

Conclusions:

• A specific subset of structural determinants is critical for binding to anti-p-aminoclonidine antibodies.
• These determinants are involved in ligand interaction with imidazole and alpha 2-adrenergic receptors.
• Clonidine-displacing substance likely contains these determinants, including imidazol(in)e and phenyl ring systems.