Receptors mediating the effects of 5-hydroxytryptamine on the tracheal vasculature and smooth muscle of sheep.
1. The effects of 5-hydroxytryptamine (5-HT) and the selective 5-HT3 receptor agonist 2-methyl-5-HT were examined on the tracheal vasculature in anaesthetised, paralysed and artificially ventilated sheep. The cranial tracheal arteries were perfused with blood at constant flow and perfusion pressure was measured. 5-HT and 2-methyl-5-HT were injected into the arterial perfusate. Changes in tracheal smooth muscle tone were also measured. 2. 5-HT contracted the tracheal smooth muscle. This contraction was not affected by the 5-HT2 receptor antagonist ketanserin, but was blocked by the combined '5-HT1-like' and 5-HT2 receptor antagonist methysergide. 2-methyl-5-HT had no effect on the tracheal smooth muscle. 3. 5-HT had a complex action on the tracheal vasculature producing either a biphasic change (vasoconstriction followed by dilatation) or just a constriction. 2-methyl-5-HT had a weak vasoconstrictor effect. 4. The vasoconstrictions produced by 5-HT and 2-methyl-5-HT were blocked by ketanserin. The vasodilatation produced by 5-HT was resistant to ketanserin but was antagonised by methysergide. 5. Thus 5-HT contracts the tracheal smooth muscle of sheep by stimulating '5-HT1-like' receptors. 5-HT constricts the tracheal vascular bed by stimulating 5-HT2 receptors or dilates the vascular bed by stimulating '5-HT1-like' receptors. 5-HT3 receptors appear not to be involved in the responses of the tracheal vasculature or smooth muscle to 5-HT.
Webber
S E
SE
Department of Physiology, St George's Hospital Medical School, London.
Salonen
R O
RO
Widdicombe
J G
JG
D000818:Animals; D005260:Female; D066298:In Vitro Techniques; D007650:Ketanserin / Q000494:pharmacology; D008297:Male; D008784:Methysergide / Q000494:pharmacology; D009129:Muscle Tonus / Q000187:drug effects; D009130:Muscle, Smooth / Q000378:metabolism* / Q000502:physiology; D010477:Perfusion; D011985:Receptors, Serotonin / Q000502:physiology*; D012701:Serotonin / Q000031:analogs & derivatives / Q000494:pharmacology / Q000502:physiology; D012702:Serotonin Antagonists / Q000494:pharmacology; D012756:Sheep; D014132:Trachea / Q000378:metabolism / Q000502:physiology
D011985:Receptors, Serotonin; D012702:Serotonin Antagonists; D012701:Serotonin; C045918:2-methyl-5-HT; D007650:Ketanserin; D008784:Methysergide