Study of the mechanisms involved in adenosine-5'-O-(2-thiodiphosphate) induced relaxation of rat thoracic aorta and pancreatic vascular bed.

1. The endothelium-dependent relaxation of blood vessels induced by P2Y-purinoceptor activation has often been shown to involve prostacyclin and/or nitric oxide (NO) release. In this work, we have investigated the mechanisms involved in the relaxant effect of the P2Y agonist, adenosine -5'-O-(2-thiodiphosphate) (ADP beta S) using two complementary preparations: rat pancreatic vascular bed and aortic ring. 2. On the pancreatic vascular bed, ADP beta S (1.5 and 15 microM) infused for 30 min induced a concentration-dependent vasodilatation; it was progressive during the first 10 min (first period) and sustained from 10 to 30 min (second period). Indomethacin (10 microM) delayed ADP beta S-induced vasodilatation (1.5 and 15 microM) by about 6 min. N omega-nitro-L-arginine methyl ester (L-NAME) (200 microM) suppressed the relaxation for about 5 min but thereafter ADP beta S at the two concentrations progressively induced an increase in the flow rate. Even the co-administration of L-NAME and indomethacin did not abolish the ADP beta S-induced vasorelaxation. 3. On 5-hydroxy tryptamine (5-HT) precontracted rings mounted in isometric conditions in organ baths, we observed that ADP beta S induced a concentration-dependent relaxation of rings with a functional endothelium; this effect was stable for 25 min. The ADP beta S relaxant effect was strongly inhibited by Reactive Blue 2 (30 microM) and was suppressed by pretreatment of rings with saponin (0.05 mg ml-1 for 30 min), which also abolished the acetylcholine-induced relaxation. 4. ADP beta S-induced relaxation of 5-HT precontracted rings is largely inhibited by indomethacin (100 or 10 microM) or L-NAME (100 microM). 5. We conclude that: the ADP beta S-induced relaxation is endothelium-dependent, mediated by P2Y-purinoceptors, and at least in part linked to NO and prostacyclin release, depending on the preparation used. Furthermore, on the pancreatic vascular bed, (an)other mechanism(s) than prostacyclin and NO releases may be involved in ADP beta S-induced vasodilatation.