Background Estrogen has been reported to augment endothelium-dependent vasodilatation. The role of endogenous ovarian hormones in modulating endothelium-dependent vasodilatation, however, remains to be determined. The purpose of the present study was to investigate the effects of sex and menstrual cycle on endothelium-dependent flow-mediated vasodilatation.

Methods and Results Seventeen female volunteers 25.1±0.8 years old and 17 age-matched male volunteers were examined. We measured brachial artery diameters noninvasively using a 7.5-MHz ultrasound machine at rest, during reactive hyperemia, and after sublingual nitroglycerin administration. All female subjects were studied three times each, in three different phases of one menstrual cycle (M, menstrual phase; F, follicular phase; and L, luteal phase). Flow-mediated diameter (D) increase (%FMD; ΔD/D×100) in M, when serum estradiol level was low (121.9±12.5 pmol/L), was 11.22±0.58%, and the value was comparable to that in male subjects (10.60±0.75%). %FMD increased in F (18.20±0.81%, P<.01 versus M) and L (17.53±0.74%, P<.01 versus M), when serum estradiol level was high (F, 632.0±74.5 and L, 533.8±33.4 pmol/L, P<.01 versus M). Endothelium-independent vasodilatation by nitroglycerin increased in both F and L. However, the increment was smaller than that of %FMD.

Conclusions Endothelium-dependent vasodilatation varies during the menstrual cycle. The endogenous estradiol may be involved in this menstrual cycle–related vasodilatation.