An antiserum to idazoxan recognizes an immunoreactive substance in human serum and cerebral spinal fluid which is not agmatine.
A polyclonal antibody was generated in rabbits to an idazoxan-albumin antigen. The anti-idazoxan antiserum had high affinity for unconjugated 3H-idazoxan (Kd of 19.8 nM) in a radio-immunoassay (RIA). Of various drugs and native molecules only idazoxan potently (Ki of 24 nM) inhibited 3H-idazoxan binding to the anti-idazoxan antibody. A few drugs weakly inhibited 3H-idazoxan binding (IC50 > 605 microM) with rank order of UK 14304 > guanabenz > cirazoline > amiloride > naphazoline. Neither agmatine, an endogenous clonidine displacing substance (CDS), catecholamines or imidazoles inhibited the binding of 3H-idazoxan to the anti-idazoxan antibody. The anti-idazoxan RIA was 4-6 fold more sensitive than an antibody to para-amino clonidine. The CDS detected by ligand displacement from bovine brain dose-dependently inhibited 3H-idazoxan binding. This immunoreactive (ir-) CDS activity was present in human (0.9-4.1 U/ml) and rat sera (1-2 U/ml) and in the cerebro-spinal fluid of eight patients with serious disease of the central nervous system, but not in controls. We conclude: (1) an anti-idazoxan RIA is a sensitive, selective and clinically applicable RIA for measuring ir-CDS; (2) ir-CDS is not agmatine; (3) CDS represents a family of endogenous ligands for imidazoline receptors including ir-CDS and agmatine.
Wang
H
H
Department of Neurology and Neuroscience, Cornell University Medical College, New York, NY 10021, USA.
Regunathan
S
S
McGowan
D
D
Bramwell
S
S
Reis
D J
DJ
D000376:Agmatine / Q000276:immunology* / Q000494:pharmacology; D000818:Animals; D000918:Antibody Specificity; D000941:Antigens / Q000276:immunology; D002417:Cattle; D003000:Clonidine / Q000097:blood* / Q000134:cerebrospinal fluid* / Q000276:immunology; D006801:Humans; D019329:Idazoxan / Q000276:immunology*; D054755:Imidazoline Receptors; D007106:Immune Sera / Q000276:immunology*; D011863:Radioimmunoassay; D051381:Rats; D011955:Receptors, Drug / Q000378:metabolism; D012710:Serum Albumin, Bovine / Q000276:immunology
D000941:Antigens; D054755:Imidazoline Receptors; D007106:Immune Sera; D011955:Receptors, Drug; D012710:Serum Albumin, Bovine; D000376:Agmatine; D003000:Clonidine; D019329:Idazoxan