Bessesen D H, Rupp C L, Eckel R H
Department of Medicine, University of Colorado Health Sciences Center, Denver 80262, USA.
Obes Res. 1995 Mar;3(2):191-203. doi: 10.1002/j.1550-8528.1995.tb00135.x.
Despite increasing interest in the role that fuel partitioning plays in determining body composition, the relative importance of oxidative versus storage pathways in the clearance of dietary fat remains unclear. A widely held view is that the primary destination of chylomicron triglyceride fatty acids (TGFA) is adipose tissue, and the primary source of lipid fuel for skeletal muscle is non-esterified fatty acids (NEFA). An alternate view is that muscle, not adipose tissue, is the primary site of TGFA clearance. This view is supported by estimates of the total lipoprotein lipase content of muscle and adipose tissue. To directly study the partitioning of dietary fat between oxidation and storage, 14C-labeled oleic acid was fed to Sprague Dawley rats and its metabolic rate followed over 30 days. Two hours after ingestion, more than 3.5 times as much label was found in skeletal muscle tissue (2.42 +/- 0.45 nmols) and CO2 (0.25 +/- 0.01 nmols) than was found in adipose tissue (0.71 +/- 0.14 nmols). Intramuscular triglyceride was the lipid class most extensively labeled. After skeletal muscle, liver was the next most important site of TGFA clearance. Surprisingly a substantial quantity of label remained associated with the GI tract even 24 hours after ingestion. Between 2 and 10 days following ingestion there was a net decline in the 14C content of muscle, liver and GI tract, associated with a net rise in the 14C content of adipose tissue. These findings demonstrate: 1) the importance of skeletal muscle and liver in whole organism TGFA clearance, 2) the importance of intramuscular partitioning of lipid fuels between direct oxidation and storage as TG, 3) the potentially important role of the GI tract in the delivery of dietary fat to the circulation 10-24 hours following ingestion, and 4) the stability of adipose tissue as a storage site. The complex nature of the tissue-specific clearance of TGFA over time is perhaps better described by the term "trafficking" than by the more commonly used term "partitioning." Future studies of TGFA clearance combined with sampling of relevant tissues over time will provide insight into the specific roles that abnormalities in liver, muscle and adipose tissue TGFA metabolism play in the development of hypertriglyceridemic disorders and states of increased or reduced body weight.
尽管人们对燃料分配在决定身体组成中所起的作用越来越感兴趣，但饮食脂肪清除过程中氧化途径与储存途径的相对重要性仍不明确。一种普遍的观点认为，乳糜微粒甘油三酯脂肪酸（TGFA）的主要去向是脂肪组织，而骨骼肌脂质燃料的主要来源是非酯化脂肪酸（NEFA）。另一种观点则认为，肌肉而非脂肪组织才是TGFA清除的主要部位。这一观点得到了肌肉和脂肪组织中脂蛋白脂肪酶总量估计值的支持。为了直接研究饮食脂肪在氧化和储存之间的分配情况，给斯普拉格-道利大鼠喂食14C标记的油酸，并在30天内跟踪其代谢率。摄入两小时后，在骨骼肌组织（2.42±0.45纳摩尔）和二氧化碳（0.25±0.01纳摩尔）中发现的标记物比在脂肪组织（0.71±0.14纳摩尔）中多3.5倍以上。肌肉内甘油三酯是标记最广泛的脂质类别。在骨骼肌之后，肝脏是TGFA清除的下一个最重要部位。令人惊讶的是，即使在摄入24小时后，仍有大量标记物与胃肠道相关联。在摄入后的2至10天内，肌肉、肝脏和胃肠道中14C含量出现净下降，同时脂肪组织中14C含量出现净上升。这些发现表明：1）骨骼肌和肝脏在整个机体TGFA清除中的重要性；2）肌肉内脂质燃料在直接氧化和作为TG储存之间分配的重要性；3）胃肠道在摄入后10 - 24小时将饮食脂肪输送到循环系统中的潜在重要作用；4）脂肪组织作为储存部位的稳定性。随着时间推移，TGFA在组织特异性清除方面的复杂性质，用“转运”这一术语来描述可能比更常用的“分配”术语更为恰当。未来结合相关组织随时间的采样对TGFA清除进行的研究，将深入了解肝脏、肌肉和脂肪组织中TGFA代谢异常在高甘油三酯血症疾病以及体重增加或减轻状态发展中所起的具体作用。
