17β-Estradiol induces a rapid, endothelium-dependent, sex-specific vasodilatation in spontaneous constricted rat arterioles

tive: Our purpose was to resolve the apparent contradiction between the endothelium-dependent and endothelium-independent vasodilator effects of 17β-estradiol reported in different studies. Study Design: The inner diameters of isolated pressurized spontaneously constricted muscle arterioles (diameter = 63 μm) from Wistar rats (n = 21) were measured during exposure to 17β-estradiol, and the role of the endothelium and the influence of sex were assessed. Results: A dose-dependent dilatation was observed during exposure to 17β-estradiol concentrations from 10−10 to 10−4 mol/L. Arterioles of female rats displayed significantly more dilatation than vessels from male rats. The dilatation was significantly less in endothelium-denuded arterioles or after pretreatment with and in the presence of a nitric oxide synthase inhibitor. Conclusions: These results provide strong evidence that, in addition to an endothelium-independent effect, 17β-estradiol has a dose-dependent, endothelium-mediated, rapid vasodilatory effect on muscle arterioles from the rat, which is stronger in female rats than in male rats. (Am J Obstet Gynecol 2002;187:375-81.)