L‐Carnitine is critical for protection against bioaccumulation, long‐chain fatty acid transportation and energy production. Energy production becomes important as the body maintains lean mass, repairs muscles and recovers from oxidative stress. The aim was to investigate the effects of supplemented L‐carnitine on protein turnover (PT), energy expenditure (EE) and carnitine metabolism in muscle/serum of Labrador Retrievers. In a series of experiments, all dogs were fed a low‐carnitine diet and sorted into one of two groups: L‐carnitine (LC) supplemented daily with 125 mg L‐carnitine and 3.75 g sucrose or placebo (P) supplemented with 4 g sucrose daily. The experiments consisted of analyses of muscle/serum for L‐carnitine content (EXP1), a protein turnover experiment (EXP2) and analysis of substrate utilization via indirect calorimetry (EXP3). EXP1: 20 Labradors (10 M/10 F) performed a 13 week running regimen. L‐Carnitine content was analysed in the serum and biceps femoris muscle before/after a 24.1 km run. LC serum had higher total (p < .001; p = .001), free (p < .001; p = .001) and esterified (p = .001; p = .003) L‐carnitine pre‐ and post‐run respectively. LC muscle had significantly higher free L‐carnitine post‐run (p = .034). EXP2: 26 Labs (13 M/13 F) performed a 60‐day running regimen. For the final run, half of the Labradors from each treatment rested and half ran 24.1 km. Twenty‐four Labradors received isotope infusion, and then, a biopsy of the biceps femoris of all 26 Labradors was taken to determine PT. Resting/exercised LC had a lower fractional breakdown rate (FBR) versus P group (p = .042). LC females had a lower FBR v. P females (p = .046). EXP3: Respiration of 16 Labradors (8 M/8 F) was measured via indirect calorimetry over 15 week. All dogs ran on a treadmill for 30 min at 30% VO₂ max (6.5 kph), resulting in higher maximum and mean EE in LC females v. P females (p = .021; p = .035). Implications for theory, practice and future research are discussed.

中文翻译：

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补充和锻炼的拉布拉多猎犬中的左旋肉碱代谢，蛋白质更新和能量消耗。

左旋肉碱对于防止生物蓄积，长链脂肪酸运输和能量产生至关重要。随着身体保持瘦体重，修复肌肉并从氧化应激中恢复，能量生产变得很重要。目的是研究补充左旋肉碱对拉布拉多犬肌肉/血清中蛋白质周转率（PT），能量消耗（EE）和肉碱代谢的影响。在一系列实验中，所有狗都接受低肉碱饮食，并分为两组：每天补充125 mg L-肉碱和3.75 g蔗糖的L-肉碱（LC）或补充4 g的安慰剂（P）每天蔗糖。实验包括对肌肉/血清中左旋肉碱含量的分析（EXP1），蛋白质更新实验（EXP2）和通过间接量热法（EXP3）的底物利用率分析。EXP1：20名拉布拉多（10 M / 10 F）进行了13周的跑步训练。分析血清中的左旋肉碱含量跑步24.1公里之前/之后的股二头肌。LC血清 左旋肉碱前后的总含量（p  <.001; p  = .001），游离（p  <.001; p  = .001）和酯化（p  = .001; p = .003）较高。分别运行。LC肌肉的跑后游离左旋肉碱明显更高（p  = .034）。EXP2：26个实验室（13 M / 13 F）执行了60天的跑步方案。在最后一次运行中，每种处理的拉布拉多犬中有一半休息了，而另一半则跑了24.1公里。24个拉布拉多接受了同位素输注，然后对所有26个拉布拉多的股二头肌进行活检以确定PT。静息/运动LC的分数分解率（FBR）低于P组（p  = .042）。LC女性的FBR vs P女性较低（p  = .046）。EXP3：在15周内通过间接量热法测量了16个拉布拉多（8 M / 8 F）的呼吸。所有狗在跑步机上以30％VO ₂ max（6.5 kph）的速度在跑步机上跑步30分钟，导致LC雌性对P雌性的最大EE和平均EE更高（p  = .021；p  = .035）。讨论了对理论，实践和未来研究的影响。