Research Institute for Sport and Exercise Sciences, Liverpool John Moores University, United Kingdom.
Am J Physiol Regul Integr Comp Physiol. 2011 Jun;300(6):R1437-42. doi: 10.1152/ajpregu.00042.2011. Epub 2011 Mar 30.
Early morning reduction in endothelium-dependent, flow-mediated dilation (FMD) may contribute to the high incidence of sudden cardiac death at this time of day. The mechanisms underpinning diurnal variation in FMD are unclear, but potentially relate to a circadian rhythm in sympathetic nerve activity. We hypothesized that blockade of α(1)-mediated sympathetic nerve activity would act to attenuate the diurnal variation in FMD. In a randomized and placebo-controlled design, we measured brachial artery FMD in 12 participants (mean age = 26 yr, SD = 3) at 0600 and 1600 after ingestion of an α(1)-blocker (prazosin, 1 mg/20 kg body mass) or placebo. Arterial diameter and shear rate were assessed using edge-detection software. Heart rate and blood pressure were also measured. Data were analyzed using linear mixed modeling. Following placebo, FMD was 8 ± 2% in the morning compared with 10 ± 3% in the afternoon (P = 0.04). Blockade with prazosin led to a slight but nonsignificant increase in morning FMD (P = 0.24) and a significant (P = 0.04) decrease in afternoon FMD, resulting in no diurnal variation (P = 0.20). Shear rate did not differ in the morning or afternoon under either condition (P > 0.23). Blood pressure was lower following prazosin compared with placebo (P < 0.02), an effect that was similar at both times of day (P > 0.34). Heart rate and norepinephrine levels were higher in the afternoon following prazosin. These data indicate that α(1)-adrenoreceptor activity does not explain lower morning endothelium-dependent FMD.
清晨内皮依赖性血流介导的扩张（FMD）的减少可能是导致一天中这个时候突发性心脏死亡发生率高的原因。FMD 昼夜变化的机制尚不清楚，但可能与交感神经活动的昼夜节律有关。我们假设，阻断α(1)介导的交感神经活动将有助于减轻 FMD 的昼夜变化。在一项随机对照设计中，我们在 12 名参与者（平均年龄 = 26 岁，标准差 = 3）中测量了肱动脉 FMD，分别在服用 α(1)阻滞剂（哌唑嗪，1 mg/20 kg 体重）或安慰剂后 0600 和 1600 进行测量。使用边缘检测软件评估动脉直径和剪切率。还测量了心率和血压。数据使用线性混合模型进行分析。服用安慰剂后，FMD 在早上为 8 ± 2%，下午为 10 ± 3%（P = 0.04）。哌唑嗪阻断导致早上 FMD 略有但无统计学意义的增加（P = 0.24），下午 FMD 显著降低（P = 0.04），导致无昼夜变化（P = 0.20）。在两种情况下，早上和下午的剪切率均无差异（P > 0.23）。与安慰剂相比，服用哌唑嗪后血压较低（P < 0.02），这种作用在一天中的任何时候都相似（P > 0.34）。服用哌唑嗪后下午心率和去甲肾上腺素水平升高。这些数据表明，α(1)肾上腺素能受体活性不能解释早上较低的内皮依赖性 FMD。
