Muscle Fiber Types
Charles Paul Lambert in Physiology and Nutrition for Amateur Wrestling, 2020
About 75% of the lactic acid produced during exercise is combusted or oxidized for energy. Two concepts underlie this phenomenon. The intracellular lactate shuttle and the cell–cell lactate shuttle. In the intracellular lactate shuttle concept, lactate from muscle fibers is produced and oxidized in those same muscle fiber. In the cell–cell lactate shuttle lactate is produced in fast twitch glycolytic fibers and goes to slow twitch oxidative fibers for oxidation either by going to adjacent muscle fibers or circulating through the blood (Brooks, Fahey, and Baldwin 2005). Another fate of lactate is called the Cori Cycle, where lactate produced from muscle fibers goes to the liver through the blood stream and is converted to glucose. The glucose either gets converted to glycogen in the liver or goes back to the muscle and is used for fuel (Brooks, Fahey, and Baldwin 2005). These three mechanisms would appear to be important during wrestling as it is extremely intermittent with periods of intense lactic acid building time and periods of less intense exercise where lactate could be oxidized in the cell it was produced in, oxidized in an adjacent muscle fiber, or released into the circulation for conversion to glucose by the liver (Cori Cycle) (Table 8.2).
Nutrition and fluid therapy
Professor Sir Norman Williams, Professor P. Ronan O’Connell, Professor Andrew W. McCaskie in Bailey & Love's Short Practice of Surgery, 2018
After a short fast, lasting 12 hours or less, most food from the last meal will have been absorbed. Plasma insulin levels fall and glucagon levels rise, which facilitates the conversion of liver glycogen (approximately 200 g) into glucose. The liver, therefore, becomes an organ of glucose production under fasting conditions. Many organs, including brain tissue, red and white blood cells and the renal medulla, can initially utilise only glucose for their metabolic needs. Additional stores of glycogen exist in muscle (500 g), but these cannot be utilised directly. Muscle glycogen is broken down (glycogenolysis) and converted to lactate, which is then exported to the liver where it is converted to glucose (Cori cycle). With increasing duration of fasting (>24 hours), glycogen stores are depleted and de novo glucose production from non-carbohydrate precursors (gluconeogenesis) takes place, predominantly in the liver. Most of this glucose is derived from the breakdown of amino acids, particularly glutamine and alanine as a result of catabolism of skeletal muscle (up to 75 g per day). This protein catabolism in simple starvation is readily reversed with the provision of exogenous glucose.
Features of Lipid Metabolism in Diabetes Mellitus and Ischemic Heart Disease
E.I. Sokolov in Obesity and Diabetes Mellitus, 2020
Intermediate metabolism of glucose, whose main substrate is lactate, occurs in a human organism in most tissues, where the produced lactate is oxidized in the Krebs cycle and does not enter the blood channel. The main sources of lactate are erythrocytes, the medullary substance of the kidneys, and, possibly, the brain. Under a physical load, the growth in the lactate content in the blood is due to the sharp increase in anaerobic glycolysis in the muscles. In the restoration period after a physical load, after hypoxia 10% of the lactate formed in a person’s muscles gets into the blood channel, 15% is oxidized to CO2, and 75% of the muscular lactate transforms into glycogen directly in the muscle tissues. The main pool of lactate undergoes metabolism in the Cori cycle. The lactate formed in the tissues is transferred to the kidneys and livers where it transforms into glucose. The latter again enters the tissues and is oxidized to lactate. In the long run, all the circulating lactate is utilized by the organism — 50% in the skeletal muscles and the heart, 30% in the liver, and 20% in the brain and cortical substance of the kidneys.
Approach to the patient presenting with metabolic acidosis
Published in Acta Clinica Belgica, 2019
Jill Vanmassenhove, Norbert Lameire
The normal upper limit of serum lactate level is 1–2.2 mmol/L. Normal subjects produce 15–20 mmol/kg lactic acid per day by muscle, skin, brain, gut, and erythrocytes. This lactate is metabolized by oxidation via the Krebs cycle to generate adenosine triphosphate (ATP). At least 50% of circulating lactate is taken up by cells and metabolized. Alternatively, lactate is also metabolized via the Cori cycle, resulting in glucose production. The latter takes place primarily in the liver, with a significant contribution by the renal cortex. Either of these processes results in the regeneration of the bicarbonate lost in the initial buffering of lactic acid. Most patients with lactic acidosis have elements of both overproduction and reduced removal but one of the elements is mostly the predominant cause of the metabolic acidosis. Lactate concentrations are mildly increased in various non-pathologic states (e.g. exercise), but the magnitude of the elevation is generally small. In practical terms, a lactate concentration greater than ≥ 5 mmol/L (normal is < 2.0 mmol/L) is generally accepted as evidence that the metabolic acidosis is ascribable to net lactic acid accumulation.
The association between plasma miR-122-5p release pattern at admission and all-cause mortality or shock after out-of-hospital cardiac arrest
Published in Biomarkers, 2019
Patrik Gilje, Martin Frydland, John Bro-Jeppesen, Josef Dankiewicz, Hans Friberg, Malin Rundgren, Yvan Devaux, Pascal Stammet, Mariam Al-Mashat, Jonas Jögi, Jesper Kjaergaard, Christian Hassager, David Erlinge
In the multiple linear regression model, lactate at admission was independently associated with miR-122-5p at admission. This association might reflect a reduced capability of the liver to metabolise lactate through the Cori cycle (Jansen et al.2009). However, lactate is a surrogate marker of hypoperfusion and closely relates to multiple organ dysfunction and shock (Jansen et al.2009). Our results are in line with previous findings in a pig cardiogenic shock model, where miR-122-5p increased rapidly after induction of shock and was correlated to pH and MAP during chock (Andersson et al.2012). We did not observe an association between MAP and miR-122-5p at admission but MAP is an inadequate marker of circulatory failure due to the common use of vasopressors in the post cardiac arrest setting. Due to the acute increase of miR-122-5p during the first hours after OHCA and its association with lactate at admission, one could speculate that miR-122-5p might be a hyper-acute marker of circulatory collapse and a very early marker of liver dysfunction. On the other hand, patients with shock at admission in the present study had only a non-significant increase of miR-122-5p compared to patients without shock (p = 0.14) and the logistic regression model could not detect any association between miR-122-5p at admission and shock at admission. However, since only 17 patients (10%) had shock at admission this might be a type II error and larger studies are needed to further investigate miR-122-5p as a marker of shock.
Glutathione reductase and catalase as potential biomarkers for synergistic intoxication of pesticides in fish
Published in Biomarkers, 2019
Ankur Khare, Naina Chhawani, Kanchan Kumari
LDH is a marker enzyme for cardiac function and indicates the aerobic capacity of the tissues and is inducible by oxygen stress. In this study, LDH activity has been studied in the muscle, serum to make a comparative evaluation of muscle metabolism following the treatment of the two pesticides individually and in combination. The concomitant increase in LDH levels were observed in the fish till 96 h of the study in synergistic group. This shift in anaerobic respiration was a defense mechanism to cope up with the pollutant stress. To overcome the stress and oxygen debts, muscle glycogen breaks down to glucose and favors anaerobic catabolism of glucose to lactate in muscles through Cori cycle (Abhijit et al.2016, Das et al.2004, Khan et al.2008). Next to this, lactate in mitochondria coverts to pyruvate that enters the tricarboxylic acid (TCA) cycle and supply energy in the form of adenosine triphosphate (ATP) to fish body to cope in conditions of stress. Therefore, in this study, LDH activity elevates favoring anaerobic metabolism over the aerobic one. Similar findings have been reported by Kumari and Sinha (2010) and Abhijit et al. (2016) in toad, Bufo melanostictus and Catla Catla, respectively as a function of methyl parathion.
Related Knowledge Centers
- Glucose
- Glycogen
- Pentose Phosphate Pathway
- Lactic Acid
- Glycogenolysis
- Skeletal Muscle
- Glycolysis
- Adenosine Triphosphate
- Glucose 1-Phosphate
- Glucose 6-Phosphate