title: The coexistence of adenosine A1 and A2 receptors in guinea-pig aorta.
abstract: The effects of adenosine, 5'-(N-ethyl)carboxamidoadenosine (NECA), 2-chloroadenosine (2-CA), N6-cyclohexyladenosine (CHA) and N6(R-2-phenylisopropyl)-adenosine (R-PIA) on the tone of phenylephrine-constricted guinea-pig isolated aorta have been examined. For aortic relaxation the analogues exhibited the following rank order of potency: NECA greater than adenosine greater than 2-CA greater than R-PIA greater than CHA. This is consistent with previous reports that relaxation of this tissue is mediated by the adenosine A2 receptor. An unexpected finding was that R-PIA, 2-CA and CHA all induced contractions at concentrations lower than were required for relaxation, giving a biphasic dose-response curve. Neither NECA nor adenosine contracted the aorta. This is consistent with activation of vascular A1 receptors. An A1-selective concentration of the antagonist 1,3-dipropyl-8-cyclopentyl xanthine abolished the contraction elicited by R-PIA in the guinea-pig aorta. This further suggests that the contraction is mediated by A1 receptors.
authors: Bioscience Department, ICI Pharmaceuticals, Macclesfield, Cheshire, U.K.
authors: S M
authors: SM
authors: Stoggall
authors: J S
authors: JS
authors: Shaw
mesh_terms: D015762:2-Chloroadenosine / Q000494:pharmacology*; D000241:Adenosine / Q000031:analogs & derivatives* / Q000494:pharmacology*; D019830:Adenosine-5'-(N-ethylcarboxamide); D000818:Animals; D001011:Aorta / Q000187:drug effects*; D006168:Guinea Pigs; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D010656:Phenylephrine / Q000037:antagonists & inhibitors / Q000494:pharmacology; D010660:Phenylisopropyladenosine / Q000494:pharmacology; D011983:Receptors, Purinergic / Q000187:drug effects; D014665:Vasodilator Agents / Q000494:pharmacology*
chemical_list: D011983:Receptors, Purinergic; D014665:Vasodilator Agents; D015762:2-Chloroadenosine; D010656:Phenylephrine; D010660:Phenylisopropyladenosine; D019830:Adenosine-5'-(N-ethylcarboxamide); C027513:N(6)-cyclohexyladenosine; D000241:Adenosine