Departmental Bulletin Paper Action Mechanism of Iridoid Compounds on Guinea-pig Right Atrium Specimens

齊藤, 久美子  ,  酒井 淳一  ,  堀田 芳弘

 We examined the actions of iridoid compounds (aucubin (Auc), geniposidic acid (GA)) and a noniridoid compound (chlorogenic acid (CA)) contained in Eucommia leaves [1] [2], which show blood pressure-lowering effects, on the heart using right atrial specimens isolated from guinea pigs. These 3 compounds showed negative inotropic effects (NIE) and negative chronotropic effects (NCE) at a final concentration of 10 -5 or 10 -4 M in an experiment using right atrial specimens. Furthermore, pretreatment with 10 -5 M atropine (Atr) led to the disappearance of the NIE of Auc and GA. This suggests that the enhancement of the parasympathetic nerves is involved in the action mechanism of iridoid compounds, as indicated for acetylcholine (ACh). An experiment regarding the dose-response curve (DRC) of ACh using guinea-pig intestines also demonstrated that this substance acted on the same receptors. On the other hand, the NIE of CA, as a non-iridoid compound, did not disappear despite pretreatment with 10 -5 M Atr, resembling the actions of Ca antagonists. Concerning rabbit blood pressure responses, the administration of CA at 1 mg/kg decreased the blood pressure, but GA did not reduce it, suggesting that the blood pressure-lowering effects of Eucommia leaves are associated with the Ca antagonism of CA.

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