Vasorelaxation by Amentoflavone Isolated from Selaginella tamariscina

Abstract

In the courses of in vitro screening for the vasorelaxant effect of the various extracts from medicinal plants, an ethyl acetate-soluble extract of Selaginella tamariscina was found to exhibit distinctive vasorelaxant activity. Further purifications of the extract as guided by in vitro vasorelaxant assay afforded an active biflavonoid, amentoflavone. Amentoflavone induced concentration-dependent relaxation of the phenylephrine-precontracted aorta, which disappeared by removal of functional endothelium. Pretreatment of the aortic tissues with N ^G-nitro-L-arginine methyl ester (L-NAME), methylene blue, or 1H-[1] [2] [4]-oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) inhibited the relaxation induced by amentoflavone. Amentoflavone-induced relaxations were also markedly attenuated by addition of tetraethylammonium (TEA) or verapamil. However, the relaxant effect of amentoflavone was not blocked by pretreatment with indomethacin, glibenclamide, atropine, or propranolol. Incubation of endothelium-intact aortic rings with amentoflavone increased the production of cGMP, but this effect was blocked by endothelium-denudation or pretreatment with L-NAME or ODQ. These results suggest that amentoflavone relaxes vascular smooth muscle via endothelium-dependent nitric oxide-cGMP signaling, with possible involvement of non-specific K⁺ and Ca²⁺ channels.

Abbreviations

EDRF:endothelium-derived relaxing factor

EDHF:endothelium-derived hyperpolarizing factor

NO:nitric oxide

cGMP:guanosine 3′,5′-cyclic monophosphate

DMSO:dimethyl sulfoxide

L-NAME:N ^G-nitro-L-arginine methyl ester

ODQ:1H-[1,2,4]-oxadiazole-[4,3-a]-quinoxalin-1-one

IBMX:3-isobutyl-1-methylxanthine

K_Ca:Ca²⁺-dependent K⁺ channel

K_ATP:adenosine triphosphate (ATP)-sensitive K⁺ channel

TEA:tetraethylammonium

Key words

Selaginella tamariscina - amentoflavone - vasorelaxation - nitric oxide - cGMP

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