title: Three different ways in which 5-hydroxytryptamine can affect cholinergic activity in guinea-pig isolated ileum.
abstract: The effects of 5-hydroxytryptamine (5-HT) have been studied on electrically-evoked contractions mediated by cholinergic nerves in guinea-pig isolated ileum. Low concentrations of 5-HT (0.0001-0.01 microgram ml-1) caused a sustained increase in submaximal, electrically-evoked contractions. Higher concentrations of 5-HT (0.1-10 micrograms ml-1) initially evoked a fast, rapidly-fading contraction of the muscle. Subsequently, 5-HT 0.1-10 micrograms ml-1 caused a sustained reduction in the height of the electrically-evoked contractions. The effects of 5-HT 0.01 and 0.1 microgram ml-1 on the electrically-evoked contractions were not blocked by methysergide 0.1 microgram ml-1 or by hexamethonium 10 micrograms ml-1, and may be due to changes in neuronal acetylcholine (ACh) release, since contractions evoked by exogenous ACh were unaffected by 5-HT. The results therefore imply that 5-HT can affect gut cholinergic activity in at least three different ways, two of which may modulate evoked ACh release by mechanisms which may be insensitive to tachyphylaxis.
authors.forename: G J
authors.initials: GJ
authors.lastname: Sanger
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D001285:Atropine / Q000494:pharmacology; D002799:Cholinergic Fibers / Q000502:physiology*; D004558:Electric Stimulation; D005071:Evoked Potentials / Q000187:drug effects; D005260:Female; D006168:Guinea Pigs; D006584:Hexamethonium Compounds / Q000494:pharmacology; D007082:Ileum / Q000187:drug effects / Q000294:innervation*; D066298:In Vitro Techniques; D008297:Male; D008784:Methysergide / Q000494:pharmacology; D009130:Muscle, Smooth / Q000187:drug effects*; D009538:Nicotine / Q000494:pharmacology; D012701:Serotonin / Q000494:pharmacology*; D013779:Tetrodotoxin / Q000494:pharmacology
chemical_list: D006584:Hexamethonium Compounds; D012701:Serotonin; D013779:Tetrodotoxin; D009538:Nicotine; D001285:Atropine; D000109:Acetylcholine; D008784:Methysergide