Endothelium-independent Vasorelaxant Effect of the Phyto-oestrogen Biochanin A on Rat Thoracic Aorta.
Epidemiological data suggest that the incidence of cardiovascular disease is reduced in people who have a high intake of phytoestrogens. The plant-derived estrogen biochanin A is known to cause vasodilation, but its mechanisms of action remain unclear. This study was undertaken to investigate the effects and mechanisms of biochanin A on rat thoracic aorta. Isolated aortic rings were suspended in individual organ baths and isometric tension was measured. Biochanin A induced significant relaxation in rings with or without endothelium. Contractile responses induced by phenylephrine (PE), KCl and CaCl<inf>2</inf>were antagonized by 10-7~10-4mol/L biochanin A. The transient contraction elicited by PE was significantly attenuated by 10-5mol/L biochanin A in Ca2+-free medium. The relaxant effect of biochanin A was significantly inhibited by pretreatment with the K+channel antagonists tetraethylammonium and glibenclamide in endothelium-denuded aorta. We conclude that biochanin A induces an endothelium-independent relaxation in rat aortic rings. The underlying mechanism may involve the blockage of Ca2+entry through both voltage-dependent and receptor-operated Ca2+channels, the inhibition of intracellular Ca2+release, and the activation of large-conductance Ca2+-activated K+channels and ATP-sensitive K+channels.
Wang
Hui-Ping
HP
Department of Physiology, Zhejiang University School of Medicine, Hangzhou 310031, China (phone: 0086-571-87217384; fax: 0086-571-87217146).
Mei
Ru-Huan
RH
Li
Xu-Yun
XY
Zhao
Meng-Hui
MH
Lu
Yuan
Y
Xia
Qiang
Q
Bruce
Iain
I