This study was designed to investigate the effects of a series of adenosine analogues on porcine coronary artery in vitro. In both endothelium-intact and -denuded rings, 5'-(N-ethylcarboxamido) adenosine (NECA), 2-[p-(2-carboxyethyl)]phenylethylamino-5'-N-ethylcarboxamidoadenos ine (CGS-21680), 2-chloroadenosine (CAD), N6-R-phenylisopropyladenosine (R-PIA), 2-phenylaminoadenosine (PAA), N6-cyclohexyladenosine (CHA), N6-cyclopentyladenosine (CPA), and N6-S-phenylisopropyladenosine (S-PIA) produced concentration-dependent relaxations. The rank order of potency was consistent with A2-adenosine receptor identification. The xanthine adenosine antagonist, 8-(sulfophenyl) theophylline (8-SPT), attenuated the relaxant responses to all the agonists in the endothelium-intact rings and to only CAD, R-PIA, PAA, CHA, CPA, and S-PIA in the denuded preparations. Except for NECA and CGS-21680, the slopes of the relaxation curves and the dissociation constant (Kb) values for 8-SPT were similar for all agonists. In addition, endothelium removal selectively reduced the responses to NECA and CGS-21680. The adenosine receptor agonist, CGS-22988, also relaxed the denuded rings in a manner insensitive to blockade by 8-SPT. The data suggest that multiple A2-adenosine receptors exist on the smooth muscle and endothelium of porcine coronary artery, mediating relaxation. Whereas the smooth muscle contains both xanthine-sensitive and -insensitive A2-receptors, which can be activated by a wide range of adenosine agonists, the endothelium possesses xanthine-sensitive receptors that can be stimulated selectively by certain adenosine agonists, including 5'-uronamide derivatives, such as NECA and CGS-21680. The smooth muscle also appears to contain xanthine-insensitive A4-receptors activated by CGS-22988.(ABSTRACT TRUNCATED AT 250 WORDS)

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The purpose of this study was to determine whether ATP-glyburide-sensitive K+ (KATP-glyburide) channels are involved in the adenosine-induced vasorelaxation of porcine and canine epicardial vessels in vitro. Adenosine and its analogues, 2-chloroadenosine (CAD), 5'-N-ethylcarboxamidoadenosine (NECA), R-N6-(2-phenylisopropyl)adenosine (R-PIA), N6-cyclopentyladenosine (CPA), N6-[2-(3,5-dimethoxyphenyl)-2-(2-methylphenyl)]adenosine (DPMA), 2-phenylaminoadenosine (CV-1808), 2-[m-(carboxyethyl)phenylamino]-5'-N-ethylcarboxamidoadenosine (CGS-22988), 2-[(2-cyclohexylethyl)amino]adenosine (CGS-22492), 2-[(p-amino)phenethylamino]adenosine (APE), and 2-(1-octynyl)adenosine (YT-146) (10 nM-100 microM), produced concentration-dependent relaxations in endothelium-intact and -denuded arterial ring segments contracted with 30 mM KCl, 10 nM endothelin-1, or 10 microM prostaglandin F2 alpha. Sodium nitroprusside (SNP; 1 nM-10 microM) and KATP-channel activator, pinacidil (10 nM-10 microM), also produced similar vasodilatory responses. Glyburide, a KATP-channel blocker, caused a rightward shift of the concentration-response curve to pinacidil but did not alter the responses elicited by SNP or adenosine and its analogues. The data suggest that KATP-glyburide channels are not involved in the mechanism whereby adenosine and its analogues elicit their vasorelaxant response in isolated porcine or canine epicardial vessels.

The effect of adenosine, 2-chloroadenosine (CAD), and 5'-(N-ethylcarboxamido)-adenosine (NECA) on the contraction produced by phorbol 12,13-dibutyrate (PDB) was investigated in porcine coronary artery in vitro to determine whether adenosine receptor-mediated relaxation was linked to protein kinase C. Also, the coronary relaxation produced by adenosine and NECA in KCl-contracted coronary rings was investigated before and after treatment with the phospholipase C inhibitor neomycin to examine a possible link between phospholipase C and adenosine receptor-mediated relaxation. Ring segments of coronary artery were suspended in organ baths for measurement of isometric force. PDB (10 nM-1 microM) caused concentration-dependent contraction, and this response was significantly attenuated by pretreatment with the protein kinase C inhibitor staurosporine (200 nM) but not 1-(5-isoquinolinylsulfonyl)-2-methyl-piperazine (10 microM). Treatment of rings with either adenosine, CAD, or NECA (100 microM) significantly attenuated the PDB-induced contraction, whereas treatment with either sodium nitroprusside (SNP; 1 microM) or isoproterenol (Isop; 1 microM) did not affect the contraction produced by PDB. The attenuation of the PDB-induced contraction by adenosine and its analogues was blocked by prior treatment of the coronary rings with 8-phenyltheophylline (10 microM). In a separate series of experiments, pretreatment of rings with the phospholipase C inhibitor neomycin (1 mM) resulted in a significant attenuation of the relaxing response to both adenosine and NECA while having no significant effect on the relaxation-response to SNP or Isop. These results provide indirect evidence that adenosine receptor-mediated relaxation in porcine coronary artery may be linked to modulation of protein kinase C and phospholipase C.