Duran M, Loof N E, Ketting D, Dorland L
University Children's Hospital Het Wilhelmina Kinderziekenhuis, Utrecht, The Netherlands.
J Clin Chem Clin Biochem. 1990 May;28(5):359-63.
For any given tissue the normal carnitine content is that which is necessary for an optimal rate of long-chain fatty acid oxidation. Tissues especially rich in carnitine are liver, muscle and heart. The endogenous rate of carnitine biosynthesis from lysine and methionine is not known to be influenced by fluctuations in the levels of the parent amino acids, as exemplified by hypermethioninaemic patients. Inadequate dietary supply of carnitine, leading to a deficiency, may occur in vegetarians and especially in subjects on total parenteral nutrition. Premature babies are especially at risk in this respect, and this has led to the addition of carnitine to solutions for intravenous alimentation. It has been suggested that carnitine plays an important role in the intramitochondrial regulations of coenzyme A homeostasis by expelling short-chain and medium-chain acyl groups from the mitochondrion in the form of acylcarnitines. These esters are preferentially excreted into the urine and thus result in a depletion of the body's carnitine stores. Important conditions in this respect are the inherited organic acidurias and disorders of fatty acid oxidation. Urinary acylcarnitines can be identified by indirect gas chromatographic or direct mass spectrometric methods. Patients on haemodialysis treatment will lose carnitine in the dialysis fluid, whereas excessive urinary losses of free and acetylated carnitine occur in the Fanconi syndrome. Secondary carnitine deficiency may be accompanied by a moderate degree of muscular dysfunction. Reassuringly, however, no signs of hepatic or cardiac involvement, as often seen in primary carnitine deficiency, have been observed.
对于任何特定组织而言，正常的肉碱含量是长链脂肪酸氧化达到最佳速率所必需的。肉碱含量特别丰富的组织有肝脏、肌肉和心脏。从赖氨酸和蛋氨酸内源性生物合成肉碱的速率，据了解不受母体氨基酸水平波动的影响，高蛋氨酸血症患者就是例证。素食者，尤其是接受全胃肠外营养的人，可能因膳食中肉碱供应不足而导致缺乏。早产儿在这方面风险尤其高，这促使人们在静脉营养溶液中添加肉碱。有人提出，肉碱通过以酰基肉碱的形式将短链和中链酰基基团排出线粒体，在辅酶A内稳态的线粒体内调节中发挥重要作用。这些酯类优先排泄到尿液中，从而导致体内肉碱储备的消耗。这方面的重要病症是遗传性有机酸尿症和脂肪酸氧化障碍。尿酰基肉碱可通过间接气相色谱法或直接质谱法进行鉴定。接受血液透析治疗的患者会在透析液中丢失肉碱，而在范科尼综合征中会出现游离和乙酰化肉碱的过度尿流失。继发性肉碱缺乏可能伴有一定程度的肌肉功能障碍。然而，令人放心的是，未观察到原发性肉碱缺乏常见的肝脏或心脏受累迹象。
