title: Adenosine-induced vasodilation: receptor characterization in pulmonary circulation.
abstract: Adenosine mediates vascular smooth muscle relaxation in the pulmonary circulation. The A2 receptor has been suggested to mediate adenosine-induced vasodilation (AIV). In this study, the effect(s) of selective adenosine agonist and antagonist on the hypoxic pressor response (HPR) was assessed in the isolated blood-perfused rat lung. Adenosine (0.075-7.5 mM) infusion (0.125 ml/min) into the pulmonary artery dose dependently attenuated the HPR. AIV was mimicked by 10 microM 5'-(N-ethylcarboxamido)adenosine (NECA), a nonselective adenosine agonist. Adenosine- and NECA-induced vasodilation were attenuated by 67 microM 8-(p-sulfophenyl)theophylline. In contrast, NECA-induced vasodilation was not attenuated by the A1 antagonist 8-cyclopentyl-1,3-dipropylxanthine (1 microM). At 10 microM, a minimal vasodilatory effect was seen with the nonselective adenosine agonists CV-1808 and N6-(2-phenylisopropyl)adenosine (R-PIA) compared with NECA. The highly selective A2a agonist 2-[p-(2-carboxyethyl)phenyl amino]-5'-N-ethyl carboxamido adenosine (CGS-21680C, 10 microM) and A1 agonist 2-chloro-N6-cyclopentyladenosine (CCPA, 10 microM) had no vasodilatory effect. Neither the K+ channel blockers tetraethylammonium chloride (10 mM) and glibenclamide (100 microM) nor the NO synthase inhibitor N omega-nitro-L-arginine methyl ester attenuated NECA-induced vasodilation. These findings suggest that AIV is mediated via the A2b receptor and that AIV occurs via an NO-independent mechanism.
authors.affiliation: Department of Medicine, University of South Alabama College of Medicine, Mobile 36688.
authors.forename: J
authors.initials: J
authors.lastname: Haynes
authors.forename: B
authors.initials: B
authors.lastname: Obiako
authors.forename: W J
authors.initials: WJ
authors.lastname: Thompson
authors.forename: J
authors.initials: J
authors.lastname: Downey
mesh_terms: D000241:Adenosine / Q000031:analogs & derivatives / Q000494:pharmacology*; D019830:Adenosine-5'-(N-ethylcarboxamide); D000818:Animals; D001120:Arginine / Q000031:analogs & derivatives / Q000494:pharmacology; D001794:Blood Pressure / Q000187:drug effects; D000860:Hypoxia / Q000503:physiopathology; D066298:In Vitro Techniques; D008297:Male; D019331:NG-Nitroarginine Methyl Ester; D009569:Nitric Oxide / Q000037:antagonists & inhibitors; D015221:Potassium Channels / Q000502:physiology; D011652:Pulmonary Circulation / Q000187:drug effects*; D051381:Rats; D017207:Rats, Sprague-Dawley; D018047:Receptors, Purinergic P1 / Q000502:physiology*; D014664:Vasodilation / Q000187:drug effects; D014665:Vasodilator Agents / Q000494:pharmacology; D014970:Xanthines / Q000494:pharmacology
chemical_list: D015221:Potassium Channels; D018047:Receptors, Purinergic P1; D014665:Vasodilator Agents; D014970:Xanthines; C008514:methylxanthine; D009569:Nitric Oxide; D019830:Adenosine-5'-(N-ethylcarboxamide); D001120:Arginine; D000241:Adenosine; D019331:NG-Nitroarginine Methyl Ester