The Phytoestrogen Genistein Produces Acute Nitric Oxide–Dependent Dilation of Human Forearm Vasculature With Similar Potency to 17β-Estradiol

BACKGROUND: Genistein, a phytoestrogen, may have estrogenic cardioprotective actions. We investigated whether genistein influences endothelium-dependent vasodilation in forearm vasculature of healthy human subjects and compared the effects of genistein with those of 17beta-estradiol. METHODS AND RESULTS: The brachial arterial was cannulated with a 27-gauge needle for drug infusion. Forearm blood flow responses were measured with strain-gauge plethysmography. Genistein (10 to 300 nmol/min, each dose for 6 minutes) produced a dose-dependent increase in forearm blood flow from 3.4+/-0.3 to 9.6+/-1.3 mL x min(-1) x 100 mL forearm(-1) (mean+/-SEM) in men (n=9, P:<0.0001 by ANOVA). The mean forearm venous concentration of genistein during infusion of the highest dose was 1.8+/-0.3 micromol/L in 6 additional men. Genistein produced a similar increase in blood flow in premenopausal women. Daidzein, another phytoestrogen, was ineffective, but equimolar concentrations of 17beta-estradiol caused similar vasodilation to genistein. Responses to genistein and 17beta-estradiol were inhibited to the same degree by the NO synthase inhibitor N:(G)-monomethyl-L-arginine. A threshold dose of genistein potentiated the endothelium-dependent vasodilator acetylcholine but not the endothelium-independent vasodilator nitroprusside. CONCLUSIONS: Genistein causes L-arginine/NO-dependent vasodilation in forearm vasculature of human subjects with similar potency to 17beta-estradiol and potentiates endothelium-dependent vasodilation to acetylcholine.