title: Presynaptic inhibition by serotonin of cardiac sympathetic transmission in dogs.
abstract: The effect of serotonin on cardiac sympathetic transmission was investigated in vagotomized and cardiac decentralized dogs. Administration of serotonin in doses of 10-100 micrograms/kg i.v., during the resting unstimulated state caused tachycardia and pressor responses which were inhibited by cyproheptadine but not by guanethidine. The tachycardia was reduced by a beta-adrenoceptor antagonist, bufetolol. Serotonin in doses of 3-100 micrograms/kg depressed the elevated heart rate during maintained electrical stimulation of the cardiac sympathetic nerves. Cyproheptadine did not antagonize the serotonin-induced depression of the stimulation-elevated heart rate, while desipramine attenuated but did not abolish it. Serotonin did not have a significant effect on the heart rate elevated by maintained infusion of noradrenaline. The present results suggest that serotonin-induced depression of heart rate during sympathetic nerve stimulation is due to presynaptic inhibition by serotonin of cardiac sympathetic transmission which is not mediated via 'classic' tryptaminergic receptors.
mesh_terms: D000818:Animals; D001285:Atropine / Q000494:pharmacology; D003533:Cyproheptadine / Q000494:pharmacology; D004285:Dogs; D004558:Electric Stimulation; D006321:Heart / Q000294:innervation*; D006339:Heart Rate / Q000187:drug effects; D008297:Male; D009638:Norepinephrine / Q000494:pharmacology; D012701:Serotonin / Q000494:pharmacology*; D013564:Sympathetic Nervous System / Q000187:drug effects*; D009435:Synaptic Transmission / Q000187:drug effects*
chemical_list: D003533:Cyproheptadine; D012701:Serotonin; D001285:Atropine; D009638:Norepinephrine