Role of nitric oxide in adenosine receptor-mediated relaxation of porcine coronary artery

In the present study, using porcine coronary artery rings in vitro, we examined the role of the nitric oxide (NO) pathway in endothelium-dependent vasorelaxant effects of the 5'-uronamide adenosine agonists, 5'-(N- ethylcarboxamido)adenosine (NECA) and 2-[p-(2-carboxyethyl)[phenylethyl- amino-5'-N-ethylcarboxamidoadenosine (CGS-21680) as opposed to the endothelium-independent actions of the C2- and N⁶-substituted analogues, 2- chloroadenosine (CAD) and N⁶-cyclopentyladenosine (CPA). The NO synthase inhibitor, N(G)-monomethyl-L-arginine (L-NMMA, 30 μM), and the NO-destroying agent, 6-anilino-5,8-quinolinedione (LY-83583, 10 μM), attenuated the relaxations of endothelium-intact but not -denuded rings to NECA and CGS- 21680. The effect of L-NMMA on NECA-induced relaxation was reversed by L- arginine (100 μM), a substrate for NO synthesis. In the endothelium-intact tissues, both NECA and CGS-21680 elicited enhanced production of nitrite, a stable metabolite of NO. This was also attenuated by L-NMMA or endothelium removal. Furthermore, NECA (10 μM) induced augmentation of guanosine 3',5'- cyclic monophosphate (cGMP) production in the intact arteries, which was also inhibited by L-NMMA, LY-83583, or endothelium removal. In contrast, vasorelaxant responses generated by CAD and CPA were not altered by either L- NMMA or LY-83583. Both agents (10 μM) were also unable to alter nitrite and/or guanosine 3',5'-cyclic monophosphate (cGMP) levels of the coronary artery. The data suggest that endothelium-dependent relaxations of porcine coronary artery evoked by the 5'-uronamide adenosine agonists, NECA and CGS- 21680, involve the release of NO from the endothelium, and cGMP appears to be a mediator for this effect.