REGULATORY MECHANISMS
David M. Gibson, Robert A. Harris in Metabolic Regulation in Mammals, 2001
generation of 3'5' cyclic AMP when the glucagon receptor is occupied. In liver PKA stimulates glycogenosis, as previously described for epinephrine, through the increased phosphorylation of the key glycogen enzymes (figures Î.4 and $.5). In adipose tissue the hormone-sensitive lipase is phosphorylated and activated leading to the release of long-chain fatty acids that are adsorbed and transported by plasma albumin in the blood (Chapters 4 and 7). At the same time other enzymes are phosphorylated (and inactivated) in liver ami adipose that catalyze the synthesis of fattv acids, thus precluding a futile t vele (Chapter 7, l able 7.1). Acetyl-CoA carboxylase, considered a major limiting cnzvmc in fatty acid synthesis, is subject to phosphorylation by another kinase, the 5'-AMP-activated protein kinase-bicyclic system, rather than cAMP dependent protein kinase (Chapters 6 and 7). However, it is likelv that the AMI' activated kinase is activated through the inhibition of protein phosphatases by glucagon-sparkcd cAMP protein kinase. (Recall phosphorylation and inactivation of the glycogen-bound phosphatase by PKA in figure Î.5.)
Adrenoceptors: Classification and Distribution
Kenneth J. Broadley in Autonomic Pharmacology, 2017
Lipolysis, the breakdown of triglycerides to free fatty acids (FFA) and glycerol by the action of hormone-sensitive lipase, occurs in adipocytes of white (WAT) and brown adipose tissue (BAT). This enzyme catalyses the first rate-limiting step and second step of the degradation to diacylglycerol and 2-monoacylglycerol, respectively; a separate monoacylglycerol lipase causes the final release of glycerol. WAT is the fat storage tissue making up -10% of body weight of the non-obese subject. It is mobilized during fasting and by exercise. Lipolysis is also stimulated by circulating adrenaline but release of FFA is inhibited by the accompanying vasoconstriction. This latter effect is probably due to limited availability of albumin, which is necessary for the binding of FFA (Vernon & Clegg 1985). Hormone-sensitive lipase is stimulated by those hormones that increase the levels of cAMP including noradrenaline, glucagon and ACTH. Activation is thought to be due to phosphorylation of the lipase by a cAMP-dependent protein kinase. This stimulation of lipolysis is inhibited by insulin through dephosphorylation of the enzyme, although insulin does not affect basal or non-stimulated lipolysis (Belfrage 1985).
Emerging ergogenic aids for strength/power development
Jay R Hoffman in Dietary Supplementation in Sport and Exercise, 2019
A number of mechanisms have been proposed to explain body composition changes subsequent to betaine supplementation and training. Regarding loss of fat, betaine has been suggested to: 1) promote fatty acid β-oxidation via increased muscle carnitine content and carnitine palmitoyl transferase-I mediated free fatty acid translocation into the mitochondria; 2) reduce acetyl-CoA for fatty acid synthesis; 3) decrease triglyceride synthesis via reduced acetyl-CoA carboxylase, fatty acid synthase, reduced fatty acid binding protein and mRNA expression of lipoprotein lipase; 4) increase hormone sensitive lipase activity; and 5) augment the GH response and improve insulin–insulin receptor signalling (11, 23). Regarding increased LBM, betaine has been suggested to: 1) conserve methionine for protein synthesis; 2) reduce homocysteine thiolactone (which inhibits insulin/IGF-1 mediated mRNA expression) to increase protein synthesis; 3) stimulate GH (via increased secretion of GH-releasing hormone), IGF-1, insulin–insulin–receptor signalling and reduce cortisol to increase anabolism; 4) increase cellular swelling from acting as an osmolyte, which increases protein synthesis via increased integrin-G-protein-stimulated gene transcription; and 5) stimulate mammalian target of rapamycin (mTOR) pathway-induced protein synthesis (2, 11, 31). So, betaine may be involved in a series of physiological mechanisms known to affect body composition. It appears betaine supplementation combined with training is needed to produce a desired effect.
Galangin, a dietary flavonoid, ameliorates hyperglycaemia and lipid abnormalities in rats with streptozotocin-induced hyperglycaemia
Published in Pharmaceutical Biology, 2018
Amal A. Aloud, Veeramani Chinnadurai, Chandramohan Govindasamy, Mohammed A. Alsaif, Khalid S. Al-Numair
An increase in blood TG levels is a common problem in hyperglycaemic patients and plays a role in vascular complications (Naqvi et al. 2017). A previous study demonstrated defective lipoprotein lipase (LPL) activity may be responsible for hypertriglyceridemia in diabetics (Trent et al. 2014). In the present study, plasma and tissue TG levels increased significantly in diabetic rats, which might be due to defective LPL. Insulin plays an important role inhibiting hormone-sensitive lipase. In addition, glucagon and other hormones stimulate lipolysis. Therefore, higher serum lipid levels in patients with diabetes could be due to the lack of inhibition of lipolytic hormone activity on the depots (Trent et al. 2014). Antidiabetic drugs are associated with lowered plasma TG due to returning LPL to normal activity (Liu et al. 2018). Treatment with galangin led to decreased TG levels, which may be due to increased insulin secretion as a result of increased LPL activity.
Interactive effect of swimming training and fenugreek (Trigonella foenum graecum L.) extract on glycemic indices and lipid profile in diabetic rats
Published in Archives of Physiology and Biochemistry, 2023
Seyed Ali Hosseini, Khadijeh Hamzavi, Hoda Safarzadeh, Omidreza Salehi
In present study DM induction significantly increased glucose, insulin, insulin resistance, LDL, VLDL, TC and TG and decreased HDL in rats nevertheless 4 weeks of swimming training significantly enhanced glycemic indices and lipid profile in rats with DM. Exercise with the mechanism of increasing the number of GLUT-4 in the cell membrane surface, increases glucose uptake and insulin sensitivity by muscle cells as well as decreases blood glucose for 24–72 h after exercise (Zheng et al. 2020); Also, exercise by increasing catecholamines and cAMP leads to the phosphorylation of hormone-sensitive lipase in adipose tissue and muscle, and by releasing free fatty acids from adipose tissue and increasing lipid metabolism in active muscle cells improves the lipid profile (Hosseini et al. 2020). The researchers showed that 16 weeks of exercise with intensity of 27–44% of VO2max, for three days per week and 60 min per session, improved FBS, HbA1c and oxygen consumption in elderly patients with type 2 DM, but significance changes in lipid profile did not observed (Jiang et al. 2020). Intensity of exercise seems to be a factor influencing changes in lipid profile. In a meta-analysis study, researchers showed that high intensity interval training (HIIT) and moderate intensity continuous training (MICT) reduced weight, FBS and HbA1c, as well as the effect of HIIT was more desirable than MICT (Liu et al. 2019); also 4 weeks, five sessions per week and 60 min training in each session with speed of 28 m/min enhanced HDL, TC/HDL ratio, and LDL/HDL ratio (Kazeminasab et al. 2017).
4-Phenylbutyric acid and rapamycin improved diabetic status in high fat diet/streptozotocin-induced type 2 diabetes through activation of autophagy
Published in Archives of Physiology and Biochemistry, 2021
Shaimaa H. Gadallah, Hala M. Ghanem, Amany Abdel-Ghaffar, Fatma G. Metwaly, Laila K. Hanafy, Emad K. Ahmed
Also, hypertriglyceridemia, hypercholesterolemia, increase in LDL-C level, and decrease in HDL-C levels were also observed after induction of T2DM. The increased level of triglycerides in HFD/STZ-induced diabetes observed in the current study may be due to the disruptive and toxic effect of STZ on the insulin-producing β-cells of the pancreas. This results in a lack of insulin which normally activates the enzyme lipoprotein lipase that catalyses the hydrolysis of triacylglycerols in chylomicrons and VLDL. In addition, there is an increase in the activity of the hormone-sensitive lipase which catalyses the mobilization of fatty acids from the peripheral fat depots and its activity is normally inhibited by insulin (Cullen et al.1999).
Related Knowledge Centers
- Adipocyte
- Cholesteryl Ester
- Enzyme
- Ester
- Fatty Acid
- Lipase
- Triglyceride
- Gene
- Testicle
- Cholesterol