Pharmacological characterization of 5-HT receptors in parasympathetic innervation of rat heart.
A study was made of the effects of 5-hydroxytryptamine (5-HT) on bradycardia induced in vivo by electrical stimulation of the vagus nerves in pithed rats pretreated with atenolol. 5-HT significantly decreased vagally induced, but not acetylcholine-induced, bradycardia. The first effect was blocked by methiothepin, ketanserin or methiothepin with ketanserin. When 5-HT1 and 5-HT2 receptors were blocked, 5-HT produced an increase in vagally induced bradycardia. Both the inhibition and the potentiation were blocked by simultaneous pretreatment with methiothepin, ketanserin and MDL-72222. The 5-HT2 receptor agonist m-CPP (1-(3-chlorophenyl) piperazine dihydrochloride) caused an inhibition of vagally induced bradycardia whereas the 5-HT3 receptor agonist m-CPBG (1-(m-chlorophenyl)biguanide hydrochloride) produced a significant increase. The data suggest the presence of presynaptic and/or ganglionic 5-HT2 receptors in parasympathetic innervation of the rat heart, stimulation of which inhibits the release of acetylcholine. The presence of 5-HT3 receptors is also suggested, stimulation of which induces the release of acetylcholine.
Morán
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A
Departamento de Fisiología y Farmacología, Facultad de Farmacia, Universidad de Salamanca, Spain.
Velasco
C
C
Martín
M L
ML
San Román
L
L
D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D001645:Biguanides / Q000494:pharmacology; D001794:Blood Pressure / Q000187:drug effects; D003655:Decerebrate State / Q000503:physiopathology; D004558:Electric Stimulation; D006321:Heart / Q000187:drug effects / Q000294:innervation*; D006339:Heart Rate / Q000187:drug effects; D008297:Male; D010275:Parasympathetic Nervous System / Q000187:drug effects*; D010879:Piperazines / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D011985:Receptors, Serotonin / Q000187:drug effects*; D012701:Serotonin / Q000031:analogs & derivatives / Q000494:pharmacology; D012702:Serotonin Antagonists; D017366:Serotonin Receptor Agonists / Q000494:pharmacology; D014630:Vagus Nerve / Q000502:physiology
D001645:Biguanides; D010879:Piperazines; D011985:Receptors, Serotonin; D012702:Serotonin Antagonists; D017366:Serotonin Receptor Agonists; D012701:Serotonin; C065734:1-(3-chlorophenyl)biguanide; C047087:5-carboxamidotryptamine; D000109:Acetylcholine; C015068:1-(3-chlorophenyl)piperazine