The Effect of Eqoul, a Metabolite of Isoflavone, on Endothelial Cell-independent Vasodilatation of Human Uterine Artery In Vitro

BACKGROUND The purpose of this study is to investigate 1) whether equol has the direct modulation on vascular tone of endothelium-denuded human uterine artery, and 2) if present, whether this equol-induced modulation of vascular tone is mediated by intracellular calcium modulation through Ca(2+) & K(+) channels on vascular smooth muscle cell membrane. METHODS The uterine arteries were obtained at the time of hysterectomy from 15 women. The uterine smooth muscles were pretreated with phenylephrine, 10(-5) M & high KCl solution 70 mM. The equol at 6 different concentrations from 10(-11) to 10(-6) M were used for the evaluation of modulatory action of equol on precontracted vascular smooth. The cumulative concentration-response for equol were determined on phenylephrine-induced contractions and compared with the results without pretreatment. RESULTS Equol 10(-11) to 10(-6) M in concentration showed relaxation effect on vascular smooth muscle contraction which was induced by phenylephrine 10(-5) M. This relaxation effect of equol was dose-dependent. Equol in same concentrations showed no significant effects on vascular smooth muscle contraction induced by high KCI solution. Phenylephrine-induced contraction was markedly reduced from 10(-7) to 10(-4) M in concentration by pretreatment of equol, but high KCI-induced contraction was not affected by pretreatment of equol. CONCLUSIONS This vasodilatation effect of equol may be induced by calcium antagonistic action, which was mediated through antagonistic action for receptor-dependent Ca(2+) channel, but not for voltage-dependent Ca(2+) channel. As far as we know, this is the first report of phytoestrogen equol on vascular reactivity of human vessels.