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The vasorelaxant effect of evocarpine in isolated aortic strips: mode of action
J Yamahara1, G Kobayashi, H Matsuda
1Kyoto Pharmaceutical University, Japan.
Abstract:
The effect of evocarpine (EVO), a quinolone alkaloid isolated from Evodiae fructus, on Ca2+-blocking activity has been examined. In the isolated rat thoracic aorta evocarpine significantly inhibited the contraction induced by 60 mM K+ with an IC50 of 9.8 microM, and that induced by external Ca2+ in the depolarized muscle in concentrations of 10-100 microM. The relaxant effect of evocarpine and verapamil was antagonized by Bay K8644. The increase of 45Ca2+-influx induced by 60 mM K+ was significantly inhibited by 100 microM evocarpine. In the isolated rabbit thoracic aorta 100 microM evocarpine had no effect on the norepinephrine-induced contraction in normal medium or on the phasic contraction in Ca2+-free medium or on the transient relaxation induced by activation of the Na+ pump. The content of cyclic AMP or cyclic GMP was unchanged. These results suggest that evocarpine inhibits Ca2+ influx through voltage-dependent calcium channels.
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