Effects of ^<13>C-labeled carbohydrate ingestion on the cardiovascular responses to prolonged exercise

在长时间的运动中摄入碳水化合物可以提高耐力表现。然而，目前尚不清楚碳水化合物摄入是否也会影响运动对心血管的调整。为了验证这个问题，我们调查了摄入的葡萄糖和果糖氧化的时间进程以及在长时间运动中的心血管反应。10名女性志愿者在最大负荷的60%负荷下进行3次自行车运动，每次40mri(Ex1)，然后60min(Ex2)，受试者只喝水(W)或5%葡萄糖(G)或果糖(F)溶液。受试者在Ex1和Ex2之间的3.5分钟静息期内饮用单剂W或G溶液(3.4ml/kg体重)。在G或F溶液中，以~(13)C标记的稳定同位素葡萄糖或果糖(8.5 mg/kg体重)作为示踪剂溶解。通过呼气中每V^&lt；12&gt；CO2比率(^&lt；13&gt；C/^&lt；12&gt；-C比率)来评价摄入的葡萄糖或果糖的氧化。摄氧量，Me…连续记录动脉血压(MAP)、心率(HR)和大腿肌肉近红外光谱下的肌肉血流量(MBF)。基线值定义为Ex1最后10分钟的平均值，计算Ex2期间各变量较基线的变化。Ex2期间每隔5分钟监测一次感知疲劳(RPE)。在Ex2期间，G、F和W的摄氧量相同。G组MAP反应减弱，并伴有RPE、HR和MBF的降低，而F组MAP与W组相似。这些结果表明，葡萄糖摄取对长时间运动的MAP调节有减弱作用，而果糖摄取不改变MAP反应。在G中^&lt；13&gt；C/^&lt；12&gt；C比值升高之前的MAP下降与摄取葡萄糖的利用无关，可能是由胰岛素引起的胃肠道血管扩张所致。G组MAP后来的持续下降可能是由于中枢指令的激活减少和/或执行相同运动所需的肌肉纤维的激活减少所致。较少

Carbohydrate ingestion during prolonged exercise is known to improve endurance performance. It is, however, unclear whether carbohydrate ingestion also affects the cardiovascular adjustments to exercise. To verify this problem, we investigated time courses of oxidation of ingested glucose and fructose and the cardiovascular responses during prolonged exercise. Ten female volunteers exercised on a cycle ergometer at 60 % of maximal workload for first 40 miri (Ex 1) and then 60 min (Ex 2) on three occasions while subjects ingested water only (W) or 5 % of glucose (G) or fructose (F) solution. The subject drank a single bolus of W or G solution (3.4 ml/kg body wt) during 3.5-min resting period spaced between Ex 1 and Ex 2. In G or F solution, ^<13>C-labeled stable isotope glucose or fructose (8.5 mg/kg body wt) was dissolved as a tracer. Oxidation of the ingested glucose or fructose was evaluated by V^<13>CO_2 per V^<12>CO_2 ratio (^<13>C/^<12>-C ratio) in expired gases. Oxygen uptake, me … More an arterial blood pressure (MAP), heart rate (HR), and muscle blood flow (MBF) in thigh muscles measured by near-infrared spectroscopy were continuously recorded. The baseline value was defined as the average during the last 10 min of Ex 1, and the changes from the baseline was calculated for each variable during Ex 2. Rating of perceived exertion (RPE) was also monitored every 5 min during Ex 2. The oxygen uptake during Ex 2 was identical among G, F, and W. The ^<13>C/^<12>C ratio began to increase significantly from 15 mm in G and from!6 min in F and peaked at 37 min inG and at 53 min in F during Ex2. The MAP inG showed a significant decrease before the increase of ^<13>C/^<12>C ratio and sustained at the decreased level till the end of exercise, whereas the MAP in F showed similar levels as seen in W. The attenuated MAP responses in G were accompanied by lower RPE, HR, and MBF. These results indicated that the glucose ingestion had attenuating effects on the MAP adjustment to prolonged exercise whereas the fructose ingestion did not alter the MAP responses. The preceding decrease of MAP observed before the increase of ^<13>C/^<12>C ratio in G was independent of utilization of ingested glucose and probably mediated by insulin-induced vasodilatation in the gastrointestinal tract for digestion. The later sustained decreases in MAP in G were probably mediated by less activation in central command and/or the reduced activation of muscle fibers required to perform the identical exercise. Less