Skeletal muscle oxidative capacity

CN184 Plot. C., ]. F. Hocquette, ]. H. Veerkamp, D. Durand, and D. Bauchart. Effects of dietary coconut oil on fatty acid oxidation capacity of the liver, the heart and skeletal muscles in... 

Reviews by Ruderman (19) and Adibi (20,21) indicate that the branched-chain amino acids, particularly leucine, have an important role along with alanine in gluconeogenesis. Leucine and the other two branched-chain amino acids are catabolized in skeletal muscle. The nitrogen that is removed from the branched-chain amino acids in skeletal muscle is combined with pyruvate and returned to the liver as alanine. In the liver the nitrogen is removed for urea production and the carbon chain is utilized as substrate for synthesis of glucose. Adibi et al. (22) reported that during the catabolic conditions of starvation, oxidation of leucine and fatty acids increases in skeletal muscles. While glucose oxidation is reduced, the capacity for oxidation of the fatty acid palmltate more than doubled, and leucine oxidation increased by a factor of six. 

In skeletal muscle and other tissues, ATP is generated by anaerobic glycolysis when the rate of aerobic respiration is inadequate to meet the rate of ATP utilization. Under these circumstances, the rate of pyruvate production exceeds the cell s capacity to oxidize NADH in the electron transport chain, and hence, to oxidize pyruvate in the TCA cycle. The excess pyruvate is reduced to lactate. Because lactate is an acid, its accumulation affects the muscle and causes pain and swelling. 

The heart, with its huge mitochondrial content and oxidative capacity, is able to use lactate released from other tissues as a fuel. During an exercise such as bicycle riding, lactate released into the blood from skeletal muscles in the leg might be used by resting skeletal muscles in the arm. In the brain, glial cells and astrocytes produce lactate, which is used by neurons or released into the blood. 

Simoneau, J.A., Colberg, S.R., Thaete, EL, and Kelley, D.E. 1995. Skeletal muscle glycolytic and oxidative enzyme capacities are determinants of insulin sensitivity and muscle composition in obese women. EASEB Journal. 9 273-278. 

Mammalian mitochondrial P-oxidation of fatty acids, the process by which fatty acids are oxidized, provides the primary source of energy for die heart and skeletal muscle. In hver, when blood glucose levels are low, the capacity for fatty add P-oxidation... 

Hz. The recovery of PCr was slower in control subjects following electrical stimulation compared with the rate following voluntary exercise. However, the recovery rate of PCr and calculated muscle maximum oxidative capacity in patients with spinal chord injury were 52% of those following electrical stimulation in controls. The energy cost of contraction and skeletal muscle energetics in patients with chronic obstructive pulmonary disease have been... 

Exercise limitation and functional disability in COPD have a complex, multifactorial basis. Ventilatory limitation is caused by increased airways resistance, static and dynamic hyperinflation, increased elastic load to breathing, gas exchange disturbances, and mechanical disadvantage and/or weakness of the respiratory muscles (4-6). Car-diocirculatory disturbances (7,8), nutritional factors (9), and psychological factors, such as anxiety and fear, also contribute commonly to exercise intolerance. Skeletal muscle dysfunction is characterized by reductions in muscle mass (10,11), atrophy of type I (slow twitch, oxidative, endurance) (12,13) and type Ila (fast twitch) muscle fibers (14), altered myosin heavy chain expression (15), as well as reductions in fiber capillarization (16) and oxidative enzyme capacity (17,18). Such a dysfunction is another key factor that contributes... 

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