Ingestion of dietary nitrate (NO₃^-) is associated with improved exercise tolerance and reduced oxygen (O₂) cost of exercise, ascribed to enhanced mitochondrial efficiency, muscle contractile function or other factors. Nitrate ingestion has also been found to attenuate the reduction in arterial oxygen saturation (SaO₂) during apnea and prolong apneic duration. The spleen serves as a dynamic blood pool expelling erythrocytes into the circulation during apnea, and NO₃^- and nitric oxide donors may induce vasoactive effects in the mesenteric and splanchnic circulation. Our aim was to investigate the effect of ingestion of concentrated organic NO₃^- -rich beetroot juice (BR) on spleen volume and spleen contraction during apnea, and the resulting hemoglobin concentration (Hb). Eight volunteers performed two apneas of submaximal and maximal duration during prone rest ~2.5h after ingesting 70 mL of BR (~5 mmol NO₃^-) or placebo (PL; ~ 0.003 mmol NO₃^-), on separate days in weighted order. Heart rate and SaO₂ were monitored continuously and spleen diameters were measured every minute for tri-axial volume calculation. Capillary Hb samples were collected at baseline and after the maximal apnea. Baseline spleen volume was reduced by 66 ml after BR ingestion (22.9 %; p=0.026) and Hb was elevated (+3.0 %; p=0.015). During apneas spleen contraction and Hb increase were similar between BR and PL conditions (NS). The study shows that dietary NO₃^- reduces spleen volume at rest resulting in increased Hb. This spleen-induced Hb-elevation following NO₃^- ingestions represents a novel mechanism that could enhance performance in conditions involving exercise, apnea and hypoxia.

中文翻译：

---

摄入硝酸盐后脾收缩和血红蛋白升高

膳食硝酸盐摄取（NO ₃ ^- ）与改善运动耐受性和减少的氧（O相关联的₂运动的）成本，归因于提高线粒体效率，肌肉收缩功能或其它因素。还发现硝酸盐的摄入会减弱呼吸暂停期间动脉血氧饱和度（SaO ₂）的降低，并延长呼吸暂停时间。脾用作动态血池呼吸暂停期间排出的红细胞进入循环，和NO ₃ ^-和一氧化氮供体可以诱导在肠系膜和内脏循环血管活性作用。我们的目的是研究摄入浓有机NO _3-的影响^。富含甜菜根汁（BR）对呼吸暂停期间的脾脏体积和脾脏收缩，以及产生的血红蛋白浓度（Hb）。8名志愿者容易发生休息期间执行次最大和最大持续时间的2〜呼吸暂停摄取70毫升BR的（〜5毫摩尔NO后2.5小时₃ ^- ）或安慰剂（PL;〜0.003毫摩尔NO ₃ ^- ），对加权顺序分开的日子。心率和SaO ₂连续监测并每分钟测量脾脏直径以计算三轴体积。在基线和最大呼吸暂停后收集毛细管血红蛋白样品。摄入BR后，基线脾脏体积减少了66 ml（22.9％； p = 0.026），Hb升高（+ 3.0％； p = 0.015）。在呼吸暂停期间，BR和PL条件（NS）之间的脾脏收缩和Hb升高相似。研究表明，饮食NO ₃ ^-降低了在休息脾体积导致增加的血红蛋白。下面NO这脾诱导HB-海拔₃ ^-内容撷取代表一种新的机制，可以加强在涉及运动，呼吸暂停和缺氧条件下的性能。