Wray D Walter, Nishiyama Steven K, Richardson Russell S
Deptartment of Medicine, Univers9ty of Utah, VAMC SLC, Bldg. 2, Salt Lake City, UT 84132, USA.
Am J Physiol Heart Circ Physiol. 2009 Feb;296(2):H497-504. doi: 10.1152/ajpheart.01016.2008. Epub 2008 Dec 5.
alpha(1)-Adrenergic vasoconstriction during dynamic leg exercise is diminished in younger individuals, although the extent of this exercise-induced "sympatholysis" in the elderly remains uncertain. Thus, in nine young (25 +/- 1 yr) and six older (72 +/- 2 yr) healthy volunteers, we evaluated changes in leg blood flow (ultrasound Doppler) during blood flow-adjusted intra-arterial infusion of phenylephrine (PE; a selective alpha(1)-adrenergic agonist) at rest and during knee-extensor leg exercise at 20, 40, and 60% of maximal work rate (WR(max)). To probe the potential contributors to exercise-induced changes in alpha(1)-adrenergic receptor sensitivity, exercising leg O(2) consumption (Vo(2)) and lactate efflux were also evaluated (n = 10). At rest, the PE-induced vasoconstriction (i.e., decrease in leg blood flow) was diminished in older (-37 +/- 3%) compared with young (-54 +/- 4%) subjects. During exercise, the magnitude of alpha(1)-adrenergic vasoconstriction in the active leg decreased in both groups. However, compared with young, older subjects maintained a greater vasoconstrictor response to PE at 40% WR(max) (-14 +/- 3%, older; -7 +/- 2%, young) and 60% WR(max) (-11 +/- 3%, older; -4 +/- 3%, young). It is possible that this observation may be attributed to lower absolute work rates in the older group, because, for a similar absolute work rate ( approximately 10 W) and leg Vo(2) ( approximately 0.36 l/min), vasoconstriction to PE was not different between groups (-14 +/- 3%; older; -17 +/- 5%, young). Together, these data challenge the concept of reduced sympatholysis in the elderly, suggesting instead that the inhibition of alpha(1)-adrenergic vasoconstriction in the exercising leg is associated with work performed and, therefore, more closely related to the rate of oxidative metabolism than to age per se.
在动态腿部运动期间，年轻个体的α(1)-肾上腺素能血管收缩作用减弱，不过老年人运动诱导的这种“交感神经阻滞”程度仍不确定。因此，在9名年轻（25±1岁）和6名年长（72±2岁）健康志愿者中，我们评估了在静息状态以及以最大工作率（WR(max)）的20%、40%和60%进行伸膝腿部运动期间，经血流调整的动脉内输注去氧肾上腺素（PE；一种选择性α(1)-肾上腺素能激动剂）时腿部血流（超声多普勒）的变化。为探究运动诱导的α(1)-肾上腺素能受体敏感性变化的潜在影响因素，还评估了运动腿部的氧消耗（Vo(2)）和乳酸流出量（n = 10）。静息时，与年轻受试者（-54±4%）相比，年长受试者（-37±3%）中PE诱导的血管收缩（即腿部血流减少）减弱。运动期间，两组主动腿部的α(1)-肾上腺素能血管收缩幅度均降低。然而，与年轻受试者相比，年长受试者在40% WR(max)（年长受试者为-14±3%，年轻受试者为-7±2%）和60% WR(max)（年长受试者为-11±3%，年轻受试者为-4±3%）时对PE保持更大的血管收缩反应。这种观察结果可能归因于年长组较低的绝对工作率，因为对于相似的绝对工作率（约10 W）和腿部Vo(2)（约0.36 l/min），两组对PE的血管收缩反应并无差异（年长受试者为-14±3%；年轻受试者为-17±5%）。总之，这些数据对老年人交感神经阻滞减弱的概念提出了挑战，表明运动腿部α(1)-肾上腺素能血管收缩的抑制与所做的功相关，因此，与氧化代谢率的关系比与年龄本身的关系更为密切。
