Diurnal variation of flow-mediated vasodilation in healthy premenopausal women

The present study was designed to test the hypothesis of a diurnal variatio n of endothelial function. Sixteen healthy, nonsmoking women were studied, each on four occasions during one 24-h period (2:00 PM, 8:00 PM, 2:00 AM, a nd 8:00 AM). Endothelial function was assessed by ultrasound determinations of flow-mediated vasodilation (FMD%) in the brachial artery. FMD% was cont rasted with endothelium-independent vasodilation, i.e., nitroglycerine-indu ced vasodilation (NTG%). Additionally, plasma concentrations and urinary ex cretion of nitrate and cGMP were analyzed. FMD% and NTG% displayed diurnal, albeit not parallel, patterns of variation. Whereas FMD% gradually increas ed from 2: 00 PM and peaked at 2: 00 AM (means +/- SE: 3.1 +/- 0.4, 4.4 +/- 0.4, 5.1 +/- 0.9, and 3.9 +/- 0.8%), the NTG% demonstrated a nadir at 2: 0 0 AM. Plasma levels and urinary excretion of nitrate and cGMP did not displ ay diurnal variation and no clear association with the variations seen in F MD% and NTG%. This study demonstrates a diurnal variation in both endotheli um-dependent and -independent vasodilation in the brachial artery of health y women. The background and possible implication of such a variation requir e further studies.