Adenosine antagonizes the positive inotropic action mediated via beta-, but not alpha-adrenoceptors in the rabbit papillary muscle.
In the isolated rabbit papillary muscle, adenosine (1-300 microM) alone scarcely affected the basal tension developed. The positive inotropic action of isoprenaline, mediated via beta-adrenoceptors, was inhibited by adenosine in a concentration-dependent manner. Atropine (0.3 microM) abolish the inhibitory action of carbachol on the isoprenaline-induced positive inotropic action but not affect the inhibitory asction of adenosine. Adenosine failed to inhibit the positive inotropic action exerted by phenylephrine via stimulation of alpha-adrenoceptors in the presence of pindolol (30 nM). The present results indicate that the positive inotropic action was mediated via alpha-adrenoceptors whose subecllular mechanism was not susceptible to the inhibitory action of adenosine as are beta-adrenoceptors.
D000241:Adenosine / Q000494:pharmacology*; D000818:Animals; D002217:Carbachol / Q000494:pharmacology; D004347:Drug Interactions; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D009200:Myocardial Contraction / Q000187:drug effects*; D010210:Papillary Muscles / Q000187:drug effects; D010656:Phenylephrine / Q000494:pharmacology; D010869:Pindolol / Q000494:pharmacology; D011817:Rabbits; D011941:Receptors, Adrenergic / Q000187:drug effects*; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects* / Q000502:physiology; D011943:Receptors, Adrenergic, beta / Q000187:drug effects* / Q000502:physiology
D011941:Receptors, Adrenergic; D011942:Receptors, Adrenergic, alpha; D011943:Receptors, Adrenergic, beta; D010656:Phenylephrine; D002217:Carbachol; D010869:Pindolol; D000241:Adenosine; D007545:Isoproterenol