Interactions between acetylcholine, 5-hydroxytryptamine, nicotine and morphine on isolated rabbit atria.
1. The effects of 5-hydroxytryptamine (5-HT) and morphine on the responses to acetylcholine and nicotine of isolated rabbit atria were studied.2. 5-Hydroxytryptamine (10 mug/ml.) and morphine (20 mug/ml.) blocked the negative chronotropic and inotropic actions of acetylcholine.3. Nicotine (20 mug/ml.) produced stimulation of the atria, which was blocked by dichlorisoprenaline, morphine, 5-HT, bretylium and hemicholinium. Hemicholinium block was reversed by choline.4. In reserpinized preparations, nicotine produced inhibition of atria and this action was also blocked by atropine, 5-HT and morphine. Inhibition induced by nicotine was potentiated by physostigmine.5. 5-Hydroxytryptamine (20 mug/ml.) produced stimulation of atria. This was blocked by bretylium and reduced by hemicholinium. Hemicholinium block was reversed by choline.6. It is concluded that 5-HT in low concentrations acts as a weak agonist at the cholinoceptive receptors and therefore blocks the action of acetylcholine. Furthermore, nicotine and larger doses of 5-HT have actions on ganglionic structures and liberate acetylcholine, which in turn releases catecholamines.
D000109:Acetylcholine / Q000378:metabolism / Q000494:pharmacology*; D000818:Animals; D001285:Atropine / Q000494:pharmacology; D001949:Bretylium Compounds / Q000494:pharmacology; D002794:Choline / Q000494:pharmacology; D003864:Depression, Chemical; D005724:Ganglia / Q000187:drug effects; D006321:Heart / Q000187:drug effects*; D006325:Heart Atria / Q000187:drug effects; D006339:Heart Rate / Q000187:drug effects; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D009020:Morphine / Q000494:pharmacology*; D009119:Muscle Contraction / Q000187:drug effects; D009538:Nicotine / Q000494:pharmacology*; D010276:Parasympatholytics / Q000494:pharmacology; D010830:Physostigmine / Q000494:pharmacology; D011817:Rabbits; D011955:Receptors, Drug; D012110:Reserpine / Q000494:pharmacology; D012701:Serotonin / Q000494:pharmacology*; D013268:Stimulation, Chemical
D001949:Bretylium Compounds; D010276:Parasympatholytics; D011955:Receptors, Drug; D012701:Serotonin; D009538:Nicotine; D009020:Morphine; D001285:Atropine; D012110:Reserpine; D010830:Physostigmine; D007545:Isoproterenol; D002794:Choline; D000109:Acetylcholine