Ferguson Scott K, Holdsworth Clark T, Wright Jennifer L, Fees Alex J, Allen Jason D, Jones Andrew M, Musch Timothy I, Poole David C
Department of Anatomy and Physiology, Kansas State University, Manhattan, KS 66506, USA.
Department of Community and Family Medicine, Department of Medicine, Duke University, Durham, NC 27710, USA.
Nitric Oxide. 2015 Aug 1;48:38-43. doi: 10.1016/j.niox.2014.09.157. Epub 2014 Oct 2.
Nitrate (NO3(-)) supplementation via beetroot juice (BR) preferentially improves vascular conductance and O2 delivery to contracting skeletal muscles comprised predominantly of type IIb + d/x (i.e. highly glycolytic) fibers following its reduction to nitrite and nitric oxide (NO). To address the mechanistic basis for NO3(-) to improve metabolic control we tested the hypothesis that BR supplementation would elevate microvascular PO2 (PO2mv) in fast twitch but not slow twitch muscle. Twelve young adult male Sprague-Dawley rats were administered BR ([NO3(-)] 1 mmol/kg/day, n = 6) or water (control, n = 6) for 5 days. PO2mv (phosphorescence quenching) was measured at rest and during 180 s of electrically-induced 1-Hz twitch contractions (6-8 V) of the soleus (9% type IIb +d/x) and mixed portion of the gastrocnemius (MG, 91% type IIb + d/x) muscles. In the MG, but not the soleus, BR elevated contracting steady state PO2mv by ~43% (control: 14 ± 1, BR: 19 ± 2 mmHg (P < 0.05)). This higher PO2mv represents a greater blood-myocyte O2 driving force during muscle contractions thus providing a potential mechanism by which NO3(-) supplementation via BR improves metabolic control in fast twitch muscle. Recruitment of higher order type II muscle fibers is thought to play a role in the development of the VO2 slow component which is inextricably linked to the fatigue process. These data therefore provide a putative mechanism for the BR-induced improvements in high-intensity exercise performance seen in humans.
通过甜菜根汁（BR）补充硝酸盐（NO3(-)），在其还原为亚硝酸盐和一氧化氮（NO）后，优先改善血管传导以及向主要由IIb + d/x型（即高度糖酵解型）纤维组成的收缩骨骼肌的氧气输送。为了探究NO3(-)改善代谢控制的机制基础，我们测试了以下假设：补充BR会提高快肌而非慢肌中的微血管氧分压（PO2mv）。给12只年轻成年雄性Sprague-Dawley大鼠连续5天给予BR（[NO3(-)] 1 mmol/kg/天，n = 6）或水（对照组，n = 6）。在比目鱼肌（9%为IIb + d/x型）和腓肠肌混合部分（MG，91%为IIb + d/x型）处于静息状态以及180秒的1赫兹电诱导抽搐收缩（6 - 8伏）期间，测量PO2mv（磷光猝灭）。在MG中，而非比目鱼肌中，BR使收缩期稳态PO2mv升高了约43%（对照组：14 ± 1，BR组：19 ± 2 mmHg（P < 0.05））。这种较高的PO2mv代表了肌肉收缩期间更大的血液 - 肌细胞氧气驱动力，从而为通过BR补充NO3(-)改善快肌代谢控制提供了一种潜在机制。高阶II型肌纤维的募集被认为在VO2慢成分的发展中起作用，而VO2慢成分与疲劳过程密切相关。因此，这些数据为BR诱导的人类高强度运动表现改善提供了一种假定机制。
