title: Mechanism of 5-hydroxytryptamine-induced biphasic responses of fowl rectum.
abstract: The present study investigated the mechanism of the biphasic action of 5-hydroxytryptamine (5-HT) on isolated fowl rectum. 5-HT (2.6 X 10(-6) M) very often produced a biphasic response i.e., an initial relaxation followed by contraction. Tetrodotoxin completely abolished the relaxatory component and partially inhibited the contraction. On the Remak's nerve denervated preparation (in which the non-adrenergic inhibitory and non-cholinergic excitatory neural elements are eliminated), 5-HT produced only contraction. Lysergic acid diethylamide or methysergide completely blocked the contractile component and significantly inhibited the relaxation. Caffeine, given alone, reduced the relaxation without affecting the contraction caused by 5-HT. Atropine, mepyramine, propranolol, pentolinium or indomethacin did not alter the biphasic responses to 5-HT. Thus, it is concluded that the 5-HT-induced relaxation is mediated by non-adrenergic inhibitory neurons, while the contractions of the fowl rectum are partly due to a direct myogenic action and partly mediated by an indirect stimulation of non-cholinergic excitatory neurons.
mesh_terms: D000818:Animals; D002645:Chickens; D005260:Female; D008238:Lysergic Acid Diethylamide / Q000494:pharmacology; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D009433:Neural Inhibition / Q000187:drug effects; D012007:Rectum / Q000187:drug effects*; D012701:Serotonin / Q000494:pharmacology*; D013779:Tetrodotoxin / Q000494:pharmacology
chemical_list: D012701:Serotonin; D013779:Tetrodotoxin; D008238:Lysergic Acid Diethylamide