Vasorelaxant Constituents of the Leaves of Eucommia ulmoides Oliv.

摘要

Eucommia ulmoides Oliv. (Eucommiacea) is a herbal prescription for various diseases. The present study focused on the hypotensive effects ofE. ulmoides, and investigated the active constituents and mechanisms. An aqueous methanol extract of E. ulmoides leaves showed biphasic vasorelaxation (transient and slowly developing relaxations) on isolated rat aortic rings with endothelium. Transient relaxation disappeared in de-endothelialized vessels. The crude extract was fractionated by chromatographic methods with the guidance of vasorelaxant activity, and two flavonoid glycosides were isolated: isoquercitrin and astragalin. These compounds were identified using NMR studies. Both of these compounds showed slow and sustained relaxation activity against norepinephrine (NE)皿induced contraction of rat aorta with/without endothelium. After treatment with isoquercitrin or astragalin, NE-induced vasoconstriction was significantly inhibited. Isoquercitrin and astragalin also inhibited vasoconstriction induced by high-concentration potassium (60 mM) . These results suggested that inhibition by isoquercitrin and astragalin of NE-induced vasoconstriction is due to either antagonism of adrenergic receptors and inhibition of voltage-dependent Ca2+ channels, or inhibition 01intracellular calcium signaling. On the other hand, the active compound with vasorelaxant effects dependent on endothelium remained unclear.