Vasodilator response of coronary smooth muscle to the sympathetic co-transmitters noradrenaline and adenosine 5'-triphosphate.
1. Vasodilator and vasoconstrictor responses to noradrenaline (NA), adenosine and adenosine 5'-triphosphate (ATP) were examined in isolated ring segments of the left anterior descending coronary artery of the rabbit in the absence of endothelium. 2. NA caused dose-dependent relaxation of potassium-constricted vessels in the absence of beta-adrenoceptor blockade, with a pD2 of 5.96 +/- 0.21. This was inhibited by 1 microM propranolol. Constrictor responses of vessels at baseline tension were only seen at concentrations greater than 1 mM, and reached a maximum of 6% of the contraction to 30 mM KCl. 3. ATP caused relaxation of the potassium-constricted ring segments in a dose-dependent manner, although a transient constriction often preceded the relaxation. Adenosine was equipotent with ATP in producing relaxation; this was significantly inhibited by the P1-purinoceptor antagonist, 8-phenyltheophylline (8-PT). The responses to ATP were little affected by 8-PT, indicating that ATP was not acting through breakdown to adenosine. At basal tone, ATP produced transient vasoconstriction only at concentrations greater than 0.1 mM, reaching a maximum of 38% of the contraction of 30 mM KCl. 4. We conclude that in the rabbit coronary artery both NA and ATP produce vasodilatation by a direct action on the smooth muscle.
Department of Anatomy and Developmental Biology, University College, London.
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D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D003331:Coronary Vessels / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D066298:In Vitro Techniques; D008297:Male; D009129:Muscle Tonus / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects*; D018377:Neurotransmitter Agents / Q000494:pharmacology; D009638:Norepinephrine / Q000494:pharmacology*; D011817:Rabbits; D013566:Sympathomimetics / Q000494:pharmacology*; D014665:Vasodilator Agents / Q000494:pharmacology*
D018377:Neurotransmitter Agents; D013566:Sympathomimetics; D014665:Vasodilator Agents; D000255:Adenosine Triphosphate; D009638:Norepinephrine