ABSTRACT
<p><b>AIM</b>To investigate the mechanisms of vasodilatation of plant-derived estrogen biochanin A.</p><p><b>METHODS</b>Isolated aortic ring preparations from Sprague-Dawley rats were suspended in individual organ baths. The tension was measured isometrically.</p><p><b>RESULTS</b>Biochanin A at the range of 10(-9)-10(-4) mol/L provoked concentration-dependent and endothelium-independent relaxation of the rings constricted by phenylephrine (10(-5) mol/L). Biochanin A caused concentration-dependent relaxation of denuded rings precontracted with KCl (6 x 10(-2) mol/L). Glibenclamide (3 x 10(-6) mol/L), a selective inhibitor of ATP-sensitive potassium channels, and tetraethylammonium (5 x 10(-3) mol/L), a Ca2+ -activated K+ channel inhibitor, significantly attenuated the relaxation induced by biochanin A. The vasoconstriction induced by phenylephrine was decreased by biochanin A in Ca2+ -free medium.</p><p><b>CONCLUSION</b>The endothelium-independent relaxation of thoracic aorta induced by biochanin A might be mediated by ATP-sensitive K+ channels, Ca2+ -activated K+ channels and intracellular Ca2+ release from sarcoplasmic reticulum.</p>