Pharmacological characterization of a new purinergic receptor site in rabbit aorta

Abstract

1. 1. The pharmacological properties of a vasodilating purine-activated receptor that is not a P 1 or P 2-purinoceptor were investigated. 2. 2. In rabbit isolated thoracic aorta precontracted with noradrenaline, ATP induced a 50% relaxation at 0.25 mM ( EC50%); in the absence of endothelium, EC50% was 2.5 mM. 3. 3. Adenosine induced a relaxation that was not different in both the presence and absence of endothelium, being EC50% 0.48 and 0.37 mM, respectively. 4. 4. The potent and selective P 2 y -purinoceptor agonist 2-methylthio-ATP (0.03–10 μM) induced a relaxation only in the presence of endothelium. 5. 5. In de-endothelialized aorta, 8-phenyltheophilline (8-PT: P 1 antagonist) and 3,7-dimethyl-1-propargylxanthine (DMPX: A 2 antagonist) did not antagonize ATP- and adenosine-induced relaxation. 6. 6. The present data support the presence of a new site of action for purines in rabbit isolated thoracic aorta. 7. 7. A P 3 subtype of purinoceptor, that may be identified in the hypothesized “nucleotide” receptor, is proposed.