The effects of alpha-adrenoceptor antagonists on contractile responses to 5-hydroxytryptamine in dog saphenous vein.
1 5-Hydroxytryptamine (5-HT) contracted isolated saphenous vein strips of the dog, producing a biphasic concentration-effect curve. The first phase occurred with low concentrations of 5-HT (1.0 X 10(-8) TO 5.0 X 10(-6) mol/l) with a plateau between 1.0 x 10(-6) mol/l and 1.0 x 10(-5) mol/l. The second phase occurred with high concentrations of 5-HT (greater than 1.0 x 10(-5) mol/l). 2 The alpha-adrenoceptor antabonists, phentolamine (5.0 x 10(-8) to 5.0 x 10(-7) mol/l), labetalol (1.0 x 10(-6) to 1.0 x 10(-5) mol/l) and thymoxamine (1.0 x 10(-6) to 1.0 x 10(-5) mol/l), antagonized responses to high concentrations of 5-HT but responses to low concentrations of 5-HT were not antagonized. 3 The effects of high concentrations of 5-HT were antagonized by cocaine (1.0 x 10(-6) to 1.0 x 10(-5) mol/l) and were not evident in veins removed from dogs pretreated with syrosingopine. 5-HT receptors and that high concentrations of 5-HT also act indirectly on alpha-adrenoceptors by displacing noradrenaline from neuronal stores.
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology*; D000818:Animals; D001808:Blood Vessels / Q000187:drug effects*; D003042:Cocaine / Q000494:pharmacology; D004285:Dogs; D066298:In Vitro Techniques; D008729:Methoxamine / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects; D009638:Norepinephrine / Q000494:pharmacology; D012110:Reserpine / Q000494:pharmacology; D012501:Saphenous Vein / Q000187:drug effects; D012701:Serotonin / Q000494:pharmacology*
D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D012701:Serotonin; D012110:Reserpine; D008729:Methoxamine; D003042:Cocaine; D009638:Norepinephrine