Muscle glucose metabolism

Muscle glucose metabolism following exercise in the rat. J. Clin. Ihvestigation. 69, 765-793. 

Figure 25-14 Mechanism of insulin action. Binding of insulin to the extracellular a-subunit of the insulin receptor induces autophosphorylation of the -subunit of the receptor and phosphorylation of selected intracellular proteins, such as She and the IRS family,These latter phosphoproteins interact with other targets, thereby activating phosphorylation cascades, which result in glucose uptake (in adipose tissue and skeletal muscle), glucose metabolism, synthesis (of glycogen, iipid, and proteins), enhanced gene expression, cell growth, and differentiation, p, protein phosphorylation aPKC, atypical protein kinase C, See text for details.

Insulin is a peptide hormone, secreted by the pancreas, that regulates glucose metabolism in the body. Insufficient production of insulin or failure of insulin to stimulate target sites in liver, muscle, and adipose tissue leads to the serious metabolic disorder known as diabetes mellitus. Diabetes afflicts millions of people worldwide. Diabetic individuals typically exhibit high levels of glucose in the blood, but insulin injection therapy allows diabetic individuals to maintain normal levels of blood glucose. 

Antidiabetic Drugs other than Insulin. Figure 3 The antihyperglycaemic effect of metformin involves enhanced insulin-mediated suppression of hepatic glucose production and muscle glucose uptake. Metformin also exerts non-insulin-dependent effects on these tissues, including reduced fatty acid oxidation and increased anaerobic glucose metabolism by the intestine. FA, fatty acid f, increase i decrease. 

Insulin appears to activate a process that helps glucose molecules enter the cells of striated muscle and adipose tissue Figure 49-1 depicts normal glucose metabolism. Insulin also stimulates die synthesis of glycogen by die liver. In addition, insulin promotes protein syntiiesis and helps the body store fat by preventing its breakdown for energy. 

Figure 16.3 Effects of insulin on the glucose/fatty acid cycle. Insulin enhances glucose metabolism by stimulating glucose uptake by muscle and adipose tissue and by inhibiting lipolysis in adipose tissue (see Chapter 12 for the mechanism of these effects). The effect of glucose metabolism on lipolysis is via stimulation of fatty acid esterification via glycerol 3-phosphate.

Glucose transport into skeletal muscle cells via insulin-dependent glucose transport proteins in the plasma membrane (see p. 95) and subsequent glucose metabolism are depressed because of low levels of circulating insulin. 

In slow red fibers, glucose metabolism leads into the TCA cycle and metabolism is aerobic. The red appearance of these muscles comes from the large number of mitochondria in them—the iron-containing cytochromes and myoglobin give the tissue its red appearance. The leg muscles (dark meat) of birds are of this type. 

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