Research Institute for Sport and Exercise Sciences, Liverpool John Moores Univ., Henry Cotton Campus, Webster St., Liverpool L3 2ET, UK.
Am J Physiol Regul Integr Comp Physiol. 2010 Feb;298(2):R427-32. doi: 10.1152/ajpregu.00442.2009. Epub 2009 Nov 18.
It is currently unclear to what extent diurnal variation and exercise effect endothelium-dependent nitric oxide (NO)-mediated vasodilation. Therefore, we measured brachial artery flow-mediated dilation (FMD) in 10 males (mean age = 28 yr, SD = 7), before and after a bout of intermittent cycling at 70% peak oxygen uptake on separate days beginning either at 0800 or 1600. Edge-detection and wall-tracking software was used to measure changes in arterial diameter, while shear rate (SR) was assessed using simultaneously derived blood flow velocity and B-mode diameter data. The FMD data were analyzed before and after normalization for SR with repeated-measures models. Before exercise, mean + or - SD FMD was 7 + or - 3% in the morning compared with 11 + or - 6% in the afternoon (P = 0.01). This diurnal variation persisted after data were normalized for SR, which was found to be unaffected by time of day (P = 0.33). Postexercise SR was higher than at baseline (pre-exercise) (P = 0.01) to a similar extent at both times of day. FMD was unaffected by exercise in the morning (P = 0.96) but decreased by 4 + or - 3% following exercise in the afternoon (P = 0.01) so that postexercise measurements did not differ between times of day. These data indicate that endothelium-dependent FMD is lower in the morning, and this finding was not altered by normalization of FMD for diurnal variation in SR. This infers a reduced function of the intrinsic endothelial NO-vasodilator system in the morning. We also report, for the first time, that a bout of intermittent exercise abolishes this diurnal variation in endothelium-dependent FMD.
目前尚不清楚昼夜变化和运动对内皮细胞依赖性一氧化氮（NO）介导的血管舒张的影响程度。因此，我们在 10 名男性（平均年龄= 28 岁，标准差= 7）中测量了肱动脉血流介导的扩张（FMD），这些男性分别在 0800 或 1600 开始的不同日子进行了 70%峰值摄氧量的间歇性循环运动前后。边缘检测和壁跟踪软件用于测量动脉直径的变化，而使用同时得出的血流速度和 B 型直径数据评估剪切率（SR）。使用重复测量模型，在针对 SR 进行归一化后分析 FMD 数据。运动前，早晨的平均+或-标准差 FMD 为 7+或-3%，而下午为 11+或-6%（P=0.01）。这种昼夜变化在针对 SR 进行归一化后仍然存在，而 SR 不受时间影响（P=0.33）。运动后的 SR 高于基线（运动前）（P=0.01），在一天中的两个时间都达到了相似的水平。早晨的运动对 FMD 没有影响（P=0.96），但下午运动后 FMD 下降了 4+或-3%（P=0.01），因此运动后的测量结果在一天中的两个时间没有差异。这些数据表明，FMD 对内皮依赖性的早晨较低，而这种发现并未通过对 SR 昼夜变化的 FMD 进行归一化而改变。这推断出早晨内在的内皮 NO-血管舒张系统的功能降低。我们还首次报告，一次间歇性运动消除了内皮依赖性 FMD 的这种昼夜变化。
