Exercise Physiology
Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal in Principles of Physiology for the Anaesthetist, 2020
For longer periods of exercise, energy for muscle contraction is supplied by the aerobic system in which glucose, fatty acids and amino acids from food are oxidized in the mitochondria to form ATP. Fatty acids are an important source of energy for muscle cells in prolonged exercise. β-Oxidation of the fatty acids within the mitochondria produces acetyl CoA, which enters the citric acid cycle and produces ATP. When fat is oxidized to provide energy substrates, glycolysis is inhibited because phosphorylase is inhibited by glucose-6-phosphate and by ATP. The release of epinephrine during exercise activates lipoprotein lipase (which mobilizes free fatty acids from fat depots) and liver and muscle phosphorylase (which promotes glycogenolysis). Energy from carbohydrate sources supplements the supply from fat as required. In long-term exercise, glycogen stores are depleted and the ability of muscles to use fat becomes important. The aerobic system can provide energy for athletic activity for as long as nutrients last (an unlimited time) (Table 67.1).
Chemical Exchange Saturation Transfer and Amide Proton Transfer Imaging
Shoogo Ueno in Bioimaging, 2020
Glycogen is a storage form of glucose and plays an essential role in maintaining glucose homeostasis. Glycogen is a large polymer of glucose residues. When the body does not need glucose, the glucose surplus is stored as a form of glycogen in the liver and muscles. When energy is needed, glycogen can be broken down to yield glucose molecules. The CEST imaging of glycogen (glycoCEST) [6] is based on proton exchange between hydroxyl protons (−OH, 1.0 ppm downfield to water) and water protons. The initial observations were glycogen-containing phantoms at 4.7T and 9.4T and in vivo perfused mouse livers at 4.7T. In the in vivo experiment, a decline in glycoCEST signal was observed following the administration of glucagon, which induces glycogen breakdown. To date, there are only a few reports of translation into living humans. Deng et al. [75] used healthy volunteers to demonstrate that reproducing glycoCEST measurements of the liver is feasible with a clinical 3T MRI scanner and showed that compared with post-meal measurement, glycoCEST signals decreased following overnight fasting. Thus far, no study regarding clinical patients has been reported.
Endocrinology, growth and puberty
Rachel U Sidwell, Mike A Thomson in Concise Paediatrics, 2020
Blood glucose is generally maintained in the non-fasted state between 3.5 and 8.0 mmol/L. Glucose may be manufactured from glycogen, fat or protein by a process called gluconeogenesis.Glucose is consumed by the brain as a primary source of energyMuscle may utilize glucose for energy or store it as glycogenAdipose tissue is also a store for glucose and uses glucose for triglyceride synthesisThe liver is the principal site for glucose storage, where it is kept as glycogen
Platelet glycogenolysis is important for energy production and function
Published in Platelets, 2023
Kanakanagavalli Shravani Prakhya, Hemendra Vekaria, Daniёlle M. Coenen, Linda Omali, Joshua Lykins, Smita Joshi, Hammodah R. Alfar, Qing Jun Wang, Patrick Sullivan, Sidney W. Whiteheart
Glycogen is a branched polymer of glucose stored in tissues, such as the liver and muscle that is metabolized during high energy demand.1 Platelets are one of the most metabolically flexible cells in circulation.2 They are known to switch their energy production between basal Tricarboxylic Acid Cycle and Oxidative Phosphorylation (TCA/OxPhos) and aerobic glycolysis depending on oxygen tension, the availability of substrates, and their activation state.2,3 Platelets have considerable metabolizable glycogen stores, equivalent to those of skeletal muscle.4 Deleting the two major glucose transporters, GLUT1 and 3 decreases total platelet glycogen, suggesting that the stores are dynamic.5 Active enzymes involved in glycogen synthesis (glycogen synthase kinase) and breakdown (glycogen phosphorylase) are present in platelets indicating the potential for dynamic glycogen metabolism.4 Despite these insights, the functional importance of glycogen granules in specific platelet functions (activation, secretion, aggregation, and contraction) is unclear.
Rutaecarpine enhances the anti-diabetic activity and hepatic distribution of metformin via up-regulation of Oct1 in diabetic rats
Published in Xenobiotica, 2021
Xian-Mei Song, Bing-Jie Li, Yan-Yan Zhang, Wen-Jing Ge, She-Feng Zhang, Wei-Feng Cui, Geng-Sheng Li, Rui-Feng Liang
The FBG, insulin levels, HOMA-IR, and hepatic glycogen contents in diabetic rats are shown in Figure 2. The levels of FBG, insulin, and HOMA-IR in the DM groups increased significantly compared with that of the NC group but significantly decreased by metformin alone or co-administered with rutaecarpine. Furthermore, the levels of FBG, insulin, and HOMA-IR in the group treated with metformin plus rutaecarpine were slightly lower than that of the rats in the group treated with metformin alone. Glycogen is the major storage form of glucose, inhibition of hepatic glycogen degradation can reduce glucose production. The hepatic glycogen contents of the DM group decreased significantly compared to the control group but increased significantly following administration of metformin and rutaecarpine alone or in combination. These results indicated that the combination of metformin and rutaecarpine improved the insulin sensitivity and hepatic glycogen contents more effectively than metformin treatment alone in diabetic rats.
Antioxidant and antifatigue effect of a standardized fraction (HemoHIM) from Angelica gigas, Cnidium officinale, and Paeonia lactiflora
Published in Pharmaceutical Biology, 2021
Da-Ae Kwon, Yong Sang Kim, Seul-Ki Kim, Sin Hwa Baek, Hyun Kyu Kim, Hak Sung Lee
Glycogen is a complex glucose polymer that acts as a storage form for glucose in skeletal muscles and in the liver. Glycogen and glucose are energy source accessed during exercise. A reduction in blood glucose leads to physical fatigue, while increased glycogen level in the liver and muscle enhances endurance during exhaustive exercise (Wang et al. 2008). Glycogen is used in anaerobic exercise of muscle, but glycogen accumulation in liver and muscle increases exercise efficiency because glycogen produces oxalo-acetic acid to aid in efficient oxidation of fatty acids during aerobic exercise (Coyle et al. 1986). Because glycogen is required to maintain adequate blood glucose level, it is an important index of fatigue. In the HemoHIM groups, serum glucose was significantly higher than that in the control group. In addition, muscle glycogen content was significantly higher in the HemoHIM groups than it was in the control group.