AUGMENTATION OF THE VAGALLY-MEDIATED RESPONSE TO 5-HYDROXYTRYPTAMINE IN THE ANAPHYLACTICALLY-DESENSITIZED ATRIA OF GUINEA-PIGS "IN VITRO"

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Responses to several drugs were examined in the anaphylactically-desensitized atria of guinea-pigs in vitro, and compared with those in non-sensitized atria. The positive inotropic and chronotropic actions of histamine and catecholamines, or the negative inotropic and chronotropic actions of acetylcholine did not show the significant difference in these atrial preparations. However, the biphasic responses to 5-hydroxytryptamine (5-HT) and dimethylphenylpiperazinium (DMPP), which have indirect actions mediated by autonomic nerves, were significantly modified by the anaphylactic desensitization ; the stimulant action of 5-HT mediated by the released catecholamines was reduced but the vagally-mediated inhibitory action of 5-HT was augmented whereas that of DMPP was reduced. From these results, it is suggested that anaphylactic challenges of the isolated atria from sensitized guineapigs cause some functional changes in the autonomic nervous system innervated to the tissue.