Miller Benjamin F, Fattor Jill A, Jacobs Kevin A, Horning Michael A, Navazio Franco, Lindinger Michael I, Brooks George A
Department of Integrative Biology, University of California, Berkeley 94720, USA.
J Physiol. 2002 Nov 1;544(3):963-75. doi: 10.1113/jphysiol.2002.027128.
To test the hypothesis that lactate plays a central role in the distribution of carbohydrate (CHO) potential energy for oxidation and glucose production (GP), we performed a lactate clamp (LC) procedure during rest and moderate intensity exercise. Blood [lactate] was clamped at approximately 4 mM by exogenous lactate infusion. Subjects performed 90 min exercise trials at 65 % of the peak rate of oxygen consumption (V(O(2))(,peak); 65 %), 55 % V(O(2))(,peak) (55 %) and 55 % V(O(2))(,peak) with lactate clamped to the blood [lactate] that was measured at 65 % V(O(2))(,peak) (55 %-LC). Lactate and glucose rates of appearance (R(a)), disappearance (R(d)) and oxidation (R(ox)) were measured with a combination of [3-(13)C]lactate, H(13)CO(3)(-), and [6,6-(2)H(2)]glucose tracers. During rest and exercise, lactate R(a) and R(d) were increased at 55 %-LC compared to 55 %. Glucose R(a) and R(d) were decreased during 55 %-LC compared to 55 %. Lactate R(ox) was increased by LC during exercise (55 %: 6.52 +/- 0.65 and 55 %-LC: 10.01 +/- 0.68 mg kg(-1) min(-1)) which was concurrent with a decrease in glucose oxidation (55 %: 7.64 +/- 0.4 and 55 %-LC: 4.35 +/- 0.31 mg kg(-1) min(-1)). With LC, incorporation of (13)C from tracer lactate into blood glucose (L GNG) increased while both GP and calculated hepatic glycogenolysis (GLY) decreased. Therefore, increased blood [lactate] during moderate intensity exercise increased lactate oxidation, spared blood glucose and decreased glucose production. Further, exogenous lactate infusion did not affect rating of perceived exertion (RPE) during exercise. These results demonstrate that lactate is a useful carbohydrate in times of increased energy demand.
为了验证乳酸在碳水化合物（CHO）氧化势能分布和葡萄糖生成（GP）中起核心作用这一假设，我们在静息和中等强度运动期间进行了乳酸钳夹（LC）程序。通过外源性输注乳酸将血乳酸浓度钳夹在约4 mM。受试者在耗氧量峰值（V（O₂）peak）的65%（65%）、55% V（O₂）peak（55%）以及将乳酸钳夹在65% V（O₂）peak时测得的血乳酸浓度水平下进行55% V（O₂）peak的90分钟运动试验（55%-LC）。使用[3-（¹³）C]乳酸、H¹³CO₃⁻和[6,6-（²）H₂]葡萄糖示踪剂组合测量乳酸和葡萄糖的出现率（Rₐ）、消失率（Rₑ）和氧化率（Rₒₓ）。在静息和运动期间，与55%相比，55%-LC时乳酸的Rₐ和Rₑ增加。与55%相比，55%-LC期间葡萄糖的Rₐ和Rₑ降低。运动期间LC使乳酸Rₒₓ增加（55%：6.52±0.65和55%-LC：10.01±0.68 mg·kg⁻¹·min⁻¹），同时葡萄糖氧化减少（55%：7.64±0.4和55%-LC：4.35±0.31 mg·kg⁻¹·min⁻¹）。使用LC时，示踪剂乳酸中的¹³C掺入血糖（L GNG）增加，而GP和计算得出的肝糖原分解（GLY）均降低。因此，中等强度运动期间血乳酸浓度升高会增加乳酸氧化，节省血糖并降低葡萄糖生成。此外，外源性输注乳酸在运动期间不影响主观用力感觉评分（RPE）。这些结果表明，在能量需求增加时，乳酸是一种有用的碳水化合物。
