Relaxation of the ovine isolated iris sphincter by adenosine receptor agonists: lack of effect of adenosine A1 and A2 receptor antagonists.
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.
Hourani
S M
SM
School of Biological Sciences, University of Surrey, Guildford, UK. s.hourani@surrey.ac.uk
Smith
N C
NC
Nettell
J J
JJ
Hall
J M
JM
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*
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