CARNITINE, METABOLISM, SUPPLEMENTATION AND EXERCISE PERFORMANCE

Mojtaba Eizadi, Somayeh Bakhshi, Payman Abrifam, Davood Khorshidi
2011 Indian Journal of Fundamental and Applied Life Sciences   unpublished
Carnitine is an important cofactor in fat catabolism as a source of energy. This substance is both available in the diet and is made in the liver and kidneys from lysine and methionine precursors. The internal synthesis routes of carnitine seem to be sufficient to meet body needs. It is well established that in case of Carnitine deficiency, L-carnitine loading adjusts long chain fatty acid metabolism and their entry into the mitochondria. However, its role in long chain fatty acid metabolism in
more » ... acid metabolism in people without fat metabolism disorder is not yet clear. In addition L-carnitine has a potential effect on exercise capacity and activation of branched amino acid oxidation and stimulation of pyruvate dehydrogenase complex. Athletes consume L-carnitine under the illusion that it would enhance athletic performance and delay fatigue as a result of stimulation of fat oxidation and glycogen storage. INTRODUCTION Background and Identification of carnitine Carnitine was first isolated from bovine muscle in 1905 and the word carnitine is a derivative of the Latin root "carnis" meaning meat. Then in 1927 its chemical structure was identified as L-carnitine or (3 Hydroxy-4-amino methyl butyrate). In 1950 Urwin Fritz discovered that carnitine was involved in the oxidation of long chain fatty acids (LCFA) in the myocardium and other muscles, and later the role of the derivatives of this amino acid (L-carnitine, D-carnitine, acetyl-L-carnitine, Propionyl-L-carnitine) and its supplementation it in some diseases as well as healthy individuals controls was identified (Maher , 2001). Food sources and the endogenous synthesis of carnitine The bodies of humans and other mammals are able to synthesize endogenously carnitine from certain amino acids. Carnitine is synthesized by two essential amino acids; lysine and methionine particularly by the liver and the kidneys and it is stored in the skeletal muscle, heart, brain, sperms and other tissues that capable of oxidation of fatty acids. Formation of this substance needs such cofactors as vitamin C, Niacin, vitamin B and iron. In addition dietary intake of carnitine is done to maintain its reserves. In fact, 75 percent of carnitine required by the body enters the body through the diet. Red meat, poultry, fish and dairy products are considered the main sources of carnitine. Meat in adults and human milk in childhood are the main sources of carnitine. Therefore, persons with inadequate daily intake of red meat or dairy products have less reserves of carnitine. Plant foods contain smaller amounts of carnitine than animal foods. However, carnitine deficiency also occurs less frequently in these individuals. Since the healthy human body is able to produce enough of carnitine from its pre-structures. Generally, in people whose diets contain mostly plant sources, about 90 percent of carnitine synthesis is of endogenous origin (Horleys, 2003) Metabolism and excretion of carnitine The adult body contains on the average 25 grams of L-carnitine. Daily intake of 150 to 500 mmol (24 to 81 mg) is sufficient in adults. Maximum mucosal absorption is estimated to be 2 grams per day (Natali, 1993). Pharmacologic and physiological carnitine uptake is done through active transfer and passive permeation (Li et al., 1992). L-carnitine transfer is done in different tissues of the body supported by a transfer intermediary that uses the extracellular sodium as the cotransporter ion. Distribution of L-carnitine in the tissue has the half-life of 2 to 3 hours (Brass, 2000). Concentration of L-carnitine in tissues is usually several times higher than its concentration in plasma. Concentration of skeletal muscle L-carnitine is approximately 70 times the plasma concentration. The most reserves of L-carnitine in the body are skeletal muscles and heart (95%) and about 4% in the kidney, liver and other tissues and
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