title: Adenosine relaxes the aorta by interacting with an A2 receptor and an intracellular site.
abstract: The purpose of this study was to determine whether the adenosine receptor that mediates relaxation of the noradrenaline-contracted guinea-pig aorta is of the A1 or A2 subtype. 5'-N-ethylcarboxamide adenosine (NECA) and 5'-N-cyclopropylcarboxamide adenosine (NCPCA) were about 100 times more potent as relaxants of the aorta than L-N6-phenylisopropyladenosine (L-PIA) and N6-cyclohexyladenosine. L-PIA was 3 times more potent than D-PIA. These relaxations were not altered by the purine transport inhibitor dipyridamole, but were attenuated by the cell surface adenosine receptor antagonist 8-phenyltheophylline. Adenosine and 2-chloroadenosine differed from NECA and NCPCA since they evoked greater maximal relaxations and their submaximal responses were less sensitive to blockade by 8-phenyltheophylline. These differences were abolished by dipyridamole which indicates that they were due to an intracellular action of adenosine and 2-chloroadenosine. The intracellular 'P-site' agonist, 9-beta-D-xylofuranosyladenine evoked small relaxations that were attenuated by dipyridamole but were unaffected by 8-phenyltheophylline. These results indicate that adenosine can relax the aorta via interactions with a cell surface A2 receptor and with an intracellular site.
mesh_terms: D000241:Adenosine / Q000031:analogs & derivatives / Q000494:pharmacology*; D000818:Animals; D001011:Aorta / Q000187:drug effects; D004176:Dipyridamole / Q000494:pharmacology; D004347:Drug Interactions; D005260:Female; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D009126:Muscle Relaxation / Q000187:drug effects*; D009131:Muscle, Smooth, Vascular / Q000187:drug effects*; D009638:Norepinephrine / Q000494:pharmacology; D011956:Receptors, Cell Surface / Q000187:drug effects*; D011983:Receptors, Purinergic; D012977:Sodium Nitrite / Q000494:pharmacology; D013806:Theophylline / Q000031:analogs & derivatives / Q000494:pharmacology
chemical_list: D011956:Receptors, Cell Surface; D011983:Receptors, Purinergic; D004176:Dipyridamole; D013806:Theophylline; C028322:8-phenyltheophylline; D000241:Adenosine; D012977:Sodium Nitrite; D009638:Norepinephrine