Odland L M, Heigenhauser G J, Wong D, Hollidge-Horvat M G, Spriet L L
Department of Human Biology and Nutritional Sciences, University of Guelph, Ontario, Canada.
Am J Physiol. 1998 Apr;274(4):R894-902. doi: 10.1152/ajpregu.1998.274.4.R894.
The study examined the existence and regulation of fat-carbohydrate interaction during low- and moderate-intensity exercise. Eight males cycled for 10 min at 40% and 60 min at 65% maximal O2 uptake (VO2max) while infused with either Intralipid and heparin (Int) or saline (Con). Before exercise, plasma arterial free fatty acid (FFA) was 0.69 +/- 0.04 mM (Int) vs. 0.25 +/- 0.04 mM (Con). Muscle biopsies were taken at rest and at 10, 20, and 70 min of exercise. Arterial and femoral venous blood samples and expired gases were collected simultaneously throughout exercise, and blood flow was estimated from pulmonary O2 uptake and the leg arterial-venous O2 difference. Respiratory exchange ratio was higher in Con (0.94 +/- 0.01) compared with Int (0.91 +/- 0.01). Mean net leg FFA uptake was higher in Int (0.16 +/- 0.03 vs. 0.04 +/- 0.01 mmol/min), and net lactate efflux was reduced (Int, 1.55 +/- 0.36 vs. Con, 3.07 +/- 0.47 mmol/min). Leg net glucose uptake was unaffected by Int. Muscle glycogen degradation was 23% lower in Int [230 +/- 29 vs. 297 +/- 36 mmol glucosyl units/kg dry muscle (dm)]. Pyruvate dehydrogenase activity in the a form (PDHa) was lower during Int (1.61 +/- 0.17 vs. 2.22 +/- 0.24 mmol.min-1.kg wet muscle-1), and muscle citrate was higher (0.59 +/- 0.04 vs. 0.48 +/- 0.04 mmol/kg dm). Muscle lactate, phosphocreatine, ATP, acetyl-CoA, acetyl-carnitine, and P(i) were unaffected by Int. Calculated free AMP was significantly lower in Int compared with Con at 70 min of exercise (3.3 +/- 0.8 vs. 1.5 +/- 0.3 mumol/kg dm). The high FFA-induced reduction in glycogenolysis and carbohydrate oxidation at 65% VO2max appears to be due to regulation at several sites. The reduced flux through phosphorylase and phosphofructokinase during Int may have been due to reduced free AMP accumulation and increased cytoplasmic citrate. The mechanism for reduced PDH transformation to the a form is unknown but suggests reduced flux through PDH.
该研究调查了低强度和中等强度运动期间脂肪与碳水化合物相互作用的存在及调节情况。八名男性在以40%最大摄氧量（VO₂max）骑行10分钟以及以65% VO₂max骑行60分钟的过程中，分别输注了英脱利匹特和肝素（Int组）或生理盐水（Con组）。运动前，Int组的血浆动脉游离脂肪酸（FFA）为0.69±0.04 mM，而Con组为0.25±0.04 mM。在静息状态以及运动10、20和70分钟时进行肌肉活检。在整个运动过程中同时采集动脉和股静脉血样以及呼出气体，并根据肺摄氧量和腿部动静脉氧差估算血流量。Con组的呼吸交换率（0.94±0.01）高于Int组（0.91±0.01）。Int组的腿部FFA平均净摄取量更高（0.16±0.03对0.04±0.01 mmol/分钟），而乳酸净流出量减少（Int组为1.55±0.36，Con组为3.07±0.47 mmol/分钟）。Int组对腿部葡萄糖净摄取无影响。Int组的肌肉糖原降解降低了23%[230±29对297±36 mmol葡萄糖基单位/千克干肌肉（dm）]。Int组中丙酮酸脱氢酶a型（PDHa）的活性较低（1.61±0.17对2.22±0.24 mmol·min⁻¹·kg湿肌肉⁻¹），而肌肉柠檬酸含量较高（0.59±0.04对0.48±0.04 mmol/千克dm）。肌肉乳酸、磷酸肌酸、ATP、乙酰辅酶A、乙酰肉碱和无机磷酸不受Int组影响。在运动70分钟时，与Con组相比，Int组计算得出的游离AMP显著降低（3.3±0.8对1.5±0.3 μmol/千克dm）。在65% VO₂max时，高FFA诱导的糖原分解和碳水化合物氧化减少似乎是由于多个位点的调节。Int组期间通过磷酸化酶和磷酸果糖激酶的通量降低可能是由于游离AMP积累减少和细胞质柠檬酸增加。PDH转化为a型减少的机制尚不清楚，但表明通过PDH的通量降低。
