LAUSR

Exaggerated vasoconstriction plays a critical role in the development of hypertension in metabolic syndrome (MetS). A crude methanolic extract of Euryops arabicus (EA) was found to alleviate MetS-associated exaggerated vasoconstriction. The methanolic extract of EA had a direct vasodilatory effect which might account for the alleviation of vasoconstriction. Bio-guided fractionation revealed that the chloroform fraction is responsible for this effect. The observed vasodilation was not affected by Nω-nitro-L-arginine methyl ester hydrochloride (L-NAME), a nitric oxide (NO) synthase inhibitor or methylene blue (MB), a guanylate cyclase inhibitor, while it was increased by tetraethylammonium (TEA), a potassium channel blocker. In addition, the chloroform extract showed concentration-dependent inhibition of calcium-induced contraction. Chemical investigations of the chloroform fraction of EA revealed three new furanoeremophilanes, namely, 6-β-(2`-methyl-2`,3`-epoxy-propionyloxy)-10-α-H-9-oxofuranoeremophilane (4), 6- α -(2`-methyl, 2`,3`-epoxy-butyryloxy)-10-α-H-9-oxofuranoeremophilane (7), and 6-β-(2`-methyl, 2`,3`-epoxy-butyryloxy)-euryopsin (8), in addition to five other known metabolites, namely, 6-isovaleryloxy-euryopsin (1), 6-isopropionyl-euryopsin (adenostylone) (2), 6-senecioyl-euryopsin-9-one (3) 6-β -(2`-methyl-2`,3`-epoxy-butyryloxy)-10-α-H-9-oxofuranoeremophilane (5), and euryopsonol-senecioate (6). All the isolated compounds showed significant vasodilatory effects that might involve calcium channel blocking, and compounds 7 and 8 were found to be the most bioactive ones.