Abstract
We have recently purified genistin, and six kaempferol glycosides from a soy leaves
(Glycine max L. Merr.) butanol extract. Here we report the vascular effects of the extract and
purified genistin and kaempferol glycosides on contractions induced by different constricting
agonists in isolated rat carotid arteries. The butanol extract relaxed artery rings
preconstricted by 9,11-dideoxy-11α,9α-epoxy-methanoprostaglandin F2
α (U46619) or [5Z,9α,11α,13E,15S]-9,11,15-trihydroxyprosta-5,13-dienoic acid (PGF2
α) in a dose-dependent manner and this effect was independent of the presence of endothelium.
The extract also inhibited the concentration-dependent contraction to U46619 with
a slight reduction of the maximal response. The extract produced partial relaxation
of both phenylephrine-preconstricted endothelium-intact and -denuded rings. In contrast,
the extract had no effect on the contractile response to 50 mM extracellular K+. None of the six kaempferol glycosides affected vessel tension induced by U46619.
A mixture of kaempferol glycosides prepared according to their relative composition
in the extract had no effect either. However, kaempferol relaxed U46619- and high
K+-contracted rings to the same extent. Endothelium played no role in kaempferol-induced
relaxation. Genistein induced concentration-dependent relaxation and this effect was
attenuated in the endothelium-denuded rings. Genistin caused a smaller relaxant effect.
The present results indicate that a butanol extract from soy leaves causes endothelium-independent
relaxation in rat carotid artery rings. Kaempferol glycosides, accounting for ∼48
% of the extract in weight, are not the ingredients responsible for the extract-induced
relaxation. Genistein and genistin also caused relaxation, however, the dose range
is beyond that of the extract causing relaxation.
Key words
Soy leaves (Glycine max L. Merr.) - kaempferol - genistin - contraction - relaxation - carotid artery - rat
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Yu Huang, Ph. D.
Department of Physiology
Chinese University of Hong Kong
Shatin, NT, Hong Kong
Fax: +852-26035022
Email: yu-huang@cuhk.edu.hk