title: [Ethyl-3H]RS-79948-197 alpha2-adrenoceptor autoradiography validation in alpha2-adrenoceptor knockout mice.
abstract: [Ethyl-(3)H][8aR,12aS,13aS]-5,8,8a,9,10,11,12,12a,13,13a-decahydro-3-methoxy-12-(ethylsulfonyl)-6H-isoquino[2,1-g][1,6]naphthyridine ([ethyl-(3)H]RS-79948-197) was evaluated for alpha(2)-adrenoceptor autoradiography in brain sections from wild-type mice and alpha(2A)- and alpha(2ABC)-adrenoceptor knockout mice. Receptor numbers were 83% lower in cortex and 28% lower in caudate putamen of alpha(2A)-knockout mice than in wild-type mice. No specific binding was seen in alpha(2ABC)-knockout mice. [Ethyl-(3)H]RS-79948-197 saturation binding parameters were compared to those of [(3)H]2-(2,3-dihydro-2-methoxy-1,4-benzodioxan-2-yl)-4,5-dihydro-1H-imidazoline ([(3)H]RX821002) and [methyl-(3)H]17alpha-hydroxy-20alpha-yohimban-16beta-carboxylic acid methyl ester ([methyl-(3)H]rauwolscine). [Ethyl-(3)H-]RS-79948-197 detected a larger number of both alpha(2A)- and alpha(2B/C)-adrenoceptors than [(3)H]RX821002, while [methyl-(3)H]rauwolscine only underestimated the number of alpha(2A)-adrenoceptors. Oxymetazoline and prazosin competed for [ethyl-(3)H]RS-79948-197 binding with the expected rank order of affinities. Higher than necessary [ethyl-(3)H]RS-79948-197 concentrations resulted in a rapid increase in non-specific binding. Slow dissociation kinetics, high specific radioactivity and high alpha(2)-adrenoceptor affinity (slightly lower for the alpha(2A)-adrenoceptor than for the other subtypes) confer [ethyl-(3)H]RS-79948-197 distinct advantages compared to [(3)H]RX821002 for detection of alpha(2)-adrenoceptor subtypes in a mixed alpha(2)-adrenoceptor population.
authors.affiliation: Department of Pharmacology and Clinical Pharmacology, University of Turku, Itäinen Pitkäkatu 4B, FI-20520 Turku, Finland.
authors.forename: Veronica
authors.initials: V
authors.lastname: Fagerholm
authors.forename: Melanie
authors.initials: M
authors.lastname: Philipp
authors.forename: Lutz
authors.initials: L
authors.lastname: Hein
authors.forename: Mika
authors.initials: M
authors.lastname: Scheinin
mesh_terms: D058669:Adrenergic alpha-2 Receptor Antagonists; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000818:Animals; D001345:Autoradiography; D001665:Binding Sites; D001667:Binding, Competitive; D002540:Cerebral Cortex / Q000378:metabolism; D019329:Idazoxan / Q000031:analogs & derivatives* / Q000494:pharmacology; D066298:In Vitro Techniques; D007546:Isoquinolines / Q000494:pharmacology*; D008024:Ligands; D051379:Mice; D018345:Mice, Knockout; D009287:Naphthyridines / Q000494:pharmacology*; D010109:Oxymetazoline / Q000494:pharmacology; D010646:Phentolamine / Q000494:pharmacology; D011224:Prazosin / Q000494:pharmacology; D011699:Putamen / Q000378:metabolism; D011869:Radioligand Assay; D018341:Receptors, Adrenergic, alpha-2 / Q000235:genetics / Q000378:metabolism*; D014316:Tritium; D015016:Yohimbine / Q000494:pharmacology
chemical_list: D058669:Adrenergic alpha-2 Receptor Antagonists; D000316:Adrenergic alpha-Agonists; D007546:Isoquinolines; D008024:Ligands; D009287:Naphthyridines; C104875:RS 79948-197; D018341:Receptors, Adrenergic, alpha-2; D014316:Tritium; D015016:Yohimbine; D010109:Oxymetazoline; C058525:2-methoxyidazoxan; D011224:Prazosin; D019329:Idazoxan; D010646:Phentolamine