Mechanisms of the relaxations induced by 5-hydroxytryptamine on the rat isolated caecum.
The mechanism by which 5-HT produces relaxations of the rat caecum has been examined. Propranolol and cocaine markedly attenuated the relaxations whereas tetrodotoxin had no effect. Higher doses of propranolol and cocaine (greater than 10(-6) M), as well as reserpinization, converted the relaxations into contractions. There was a residual relaxation resistant to propranolol, cocaine and reserpine treatment. High doses of 5-HT (greater than 10(-5) M) were thus thought to relax the rat caecum indirectly, through the release of noradrenaline from the tissue by a tyramine-like action. The relaxations do not seem to be due only to the release of noradrenaline.
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D000818:Animals; D002432:Cecum / Q000187:drug effects / Q000502:physiology*; D003042:Cocaine / Q000494:pharmacology; D066298:In Vitro Techniques; D009119:Muscle Contraction / Q000187:drug effects; D009126:Muscle Relaxation / Q000187:drug effects; D011433:Propranolol / Q000494:pharmacology; D051381:Rats; D012110:Reserpine / Q000494:pharmacology; D012701:Serotonin / Q000502:physiology*; D012702:Serotonin Antagonists; D013618:Tachyphylaxis; D013779:Tetrodotoxin / Q000494:pharmacology
D012702:Serotonin Antagonists; D012701:Serotonin; D013779:Tetrodotoxin; D012110:Reserpine; D011433:Propranolol; D003042:Cocaine