The isoflavone metabolite dehydroequol produces vasodilatation in human resistance arteries via a nitric oxide-dependent mechanism

BACKGROUND: Isoflavones (phytoestrogens) offer potential cardioprotective benefits. We recently reported on the vasodilatory activity of the isoflavone metabolite, dehydroequol, in rat isolated aortic ring preparations. In the current study, we examine the effect of this metabolite on the vascular haemodynamic profile in human forearm resistance arteries. METHODS AND RESULTS: Responses to brachial artery infusion of dehydroequol (0.1, 0.3, 1 and 3 micromol/min) in forearm resistance arteries were obtained in six healthy males. These were done, on two separate occasions, in the absence and presence of endogenous nitric oxide synthase inhibition using NG-monomethyl-L-arginine, with sufficient sodium nitroprusside to maintain vascular tone. Dehydroequol produced a dose-dependent increase in forearm blood flow from 2.44 +/- 0.37 (basal) to 5.25 +/- 1.07 mL/100 mL/min (P < 0.05) at dehydroequol 3 micromol/min. Responses to dehydroequol were significantly dampened with inhibition of endogenous nitric oxide synthase (at 3 micromol/min: % increase in forearm blood flow fell from 114.3 +/- 22.81 to 19.45 +/- 9.19; P < 0.01). Conclusion: This is the first report of dehydroequol, a metabolite derived from the isoflavone diadzein, demonstrating potent vasodilatory properties in human resistance arteries via a nitric oxide-dependent mechanism.