Insulin carbohydrate metabolism

Factors Affecting Insulin Secretion Structure and Synthesis of Insulin Insulin Transport and Breakdown Metabolic Effects of Insulin Carbohydrate Metabolism 510 Muscle Liver... 

Storage and utilization of tissue glycogen, maintenance of blood glucose concentration, and other aspects of carbohydrate metabolism are meticulously regulated by hormones, including insulin, glucagon, epinephrine, and the glucocorticoids. 

Insulin and the oral antidiabetic dmgi, alongwith diet and exercise are die cornerstones of treatment for diabetes mellitus. They are used to prevent episodes of hypoglycemia and to normalize carbohydrate metabolism. 

Hormones have a profound effect on carbohydrate metabolism. Great interest has been aroused by reports of hormonal control of hexokinase activity by specific proteins in animal tissues.99- 100 Hexokinase action is the rate-limiting step in the uptake of D-glucose by muscle. Hexokinase is inhibited in diabetic muscle, but the inhibition can be partially reversed by insulin. A protein fraction from the anterior pituitary gland will inhibit the hexokinase of extracts of brain and muscle, and the effect of this... 

Glucagon is a second pancreatic hormone that, like insulin, influences carbohydrate metabolism. However, most of its actions oppose those of insulin. The enkephalins and endorphins are the body s natural painkillers they are thought to be responsible for runner s high. These, among many others, are proteins or are closely related to them. 

The effects of insulin on carbohydrate metabolism are discussed on p. 158. In simplified terms, they can be described as stimulation of glucose utilization and inhibition of gluconeogenesis. In addition, the transport of glucose from the blood into most tissues is also insulin-dependent (exceptions to this include the liver, CNS, and erythrocytes). 

Some of the effects of insulin on the carbohydrate metabolism (right part of the illustration) are possible without protein synthesis. In addition to Grb-2, another dimeric adaptor protein can also bind to phosphorylated IRS. This adaptor protein thereby acquires phos-phatidylinositol-3-kinase activity (PI3K) and, in the membrane, phosphorylates phospholi-... 

The signal is often modulated by integration with input from other signaling pathways (eg, the insulin/glucagon ratio is important for balancing carbohydrate metabolism in the liver). 

Kimura, Y., H. Okua, N. Shoji, T. Taemto, and S. Arichi. Effects of nonsugar fraction in black sugar on lipid and carbohydrate metabolism. Part II. New compounds inhibiting elevation of plasma insulin. Planta Med 1984 1984(5) 469-473. 

Lithium blocks the release of thyroxine (T4) and triiodothyronine (T3) mediated by thyrotropin (Kleiner et ah, 1999). This results in a decrease in circulating T4 and T3 concentrations and a feedback increase in serum thyrotropin concentration. It also inhibits thyrotropin-stimulated adenylate cyclase activity (Kleiner et ah, 1999). Lithium has varying effects on carbohydrate metabolism. Increased and decreased glucose tolerance and decreased sensitivity to insulin have been observed (Van derVelde Gordon, 1969). In animals, lithium decreases hepatic cholesterol and fatty acid synthesis. 

In diabetes mellitus, there is either insulin deficiency or insulin resistance in peripheral tissues which lead to hyperglycemia and glycosuria. Insulin corrects the various abnormalities of carbohydrate metabolism by its action on various tissues. 

Progesterone has little effect on protein metabolism. It stimulates lipoprotein lipase activity and seems to favor fat deposition. The effects on carbohydrate metabolism are more marked. Progesterone increases basal insulin levels and the insulin response to glucose. There is... 

As complex as the regulation of carbohydrate metabolism is, it is far from the whole story of fuel metabolism. The metabolism of fats and fatty acids is very closely tied to that of carbohydrates. Hormonal signals such as insulin and changes in diet or exercise are equally important in regulating fat metabolism and integrating it with that of carbohydrates. We shall return to this overall metabolic integration in mammals in Chapter 23,... 

Endocrine Influences. A number of hormones are known to influence carbohydrate metabolism in the mammal. Insulin seems to increase oxidation of glucose, lipogenesis. and glycogenesis. Its primary mode of action may be io facilitate the entry of glucose into the cell. 

Sweetener/ carbohydrate Relative sweetness (Sucrose =1) Solubility (g/100 g water at 20°C) Insulin- dependent metabolism Caloric value (kcal/g) Approval for use in soft drinks Dietary fibre approval ... 

Glucocorticoid treatment of known diabetics normally leads to deregulation, but this can be compensated for by adjusting the dose of insulin. The increased gluconeogenesis induced by glucocorticoids mainly takes place in the liver, but glucocorticoid treatment is especially likely to disturb carbohydrate metabolism in liver disease. 

Carbohydrate metabolism was known at an early date to be affected by combined oral contraceptives. A mild to moderate degree of insulin resistance was found in some investigations (167,168). However, the considerably impaired glucose tolerance described in some users in... 

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