title: Relaxation of the ovine isolated iris sphincter by adenosine receptor agonists: lack of effect of adenosine A1 and A2 receptor antagonists.
abstract: The effects of adenosine receptor ligands on the tone of the ovine isolated iris sphincter were investigated, and adenosine analogues were found to relax the carbachol-contracted tissue in a concentration-dependent manner with an order of potency of 5'-N-ethylcarboxamidoadenosine > or = 2-(p-(2-carboxyethyl)phenylethylamino)-5'-N-ethylcarboxamidoadenos ine (CGS 21680) > or = N6-cyclopentyladenosine > adenosine, consistent with activation of an adenosine A2A receptor. However, these responses were not inhibited by the non-selective adenosine A1/A2 receptor antagonist 8-p-sulphophenyltheophylline (50 microM), the selective adenosine A2A/A1 receptor antagonist N-[2-(dimethylamino)ethyl]-N-methyl-4-(2,3,6,7-tetrahydro-2,6-dioxo-1,3- dipropyl-1H-purin-8-yl)benzenesulphonamide (PD 115,199) (0.1 microM) or the non-xanthine adenosine A2A receptor antagonist (4-(2-[7-amino-2-(2-furyl) [1,2,4]-triazolo[2,3-a][1,3,5]triazin-5-yl-amino]ethyl)phenol) (ZM 241385) (0.1 microM). The relaxations cannot therefore be mediated by activation of adenosine A1, A2A or A2B receptors.
authors.affiliation: School of Biological Sciences, University of Surrey, Guildford, UK. s.hourani@surrey.ac.uk
authors.forename: S M
authors.initials: SM
authors.lastname: Hourani
authors.forename: N C
authors.initials: NC
authors.lastname: Smith
authors.forename: J J
authors.initials: JJ
authors.lastname: Nettell
authors.forename: J M
authors.initials: JM
authors.lastname: Hall
mesh_terms: D000241:Adenosine / Q000031:analogs & derivatives* / Q000494:pharmacology; D019830:Adenosine-5'-(N-ethylcarboxamide) / Q000494:pharmacology; D000818:Animals; D000959:Antihypertensive Agents / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D007498:Iris / Q000187:drug effects*; D009126:Muscle Relaxation / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects*; D010627:Phenethylamines / Q000494:pharmacology*; D058915:Purinergic P1 Receptor Antagonists; D018047:Receptors, Purinergic P1 / Q000502:physiology; D012756:Sheep; D014665:Vasodilator Agents / Q000494:pharmacology*
chemical_list: D000959:Antihypertensive Agents; D010627:Phenethylamines; D058915:Purinergic P1 Receptor Antagonists; D018047:Receptors, Purinergic P1; D014665:Vasodilator Agents; C061282:2-(4-(2-carboxyethyl)phenethylamino)-5'-N-ethylcarboxamidoadenosine; D019830:Adenosine-5'-(N-ethylcarboxamide); D000241:Adenosine