sodium-nitrite and 8-phenyltheophylline

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.

Topics: Adenosine; Animals; Aorta; Dipyridamole; Drug Interactions; Female; Guinea Pigs; In Vitro Techniques; Male; Muscle Contraction; Muscle Relaxation; Muscle, Smooth, Vascular; Norepinephrine; Receptors, Cell Surface; Receptors, Purinergic; Sodium Nitrite; Theophylline