Glycerol gluconeogenesis

Gluconeogenesis is the process of converting noncarbohydrates to glucose or glycogen. It is of particular importance when carbohydrate is not available from the diet. Significant substrates are amino acids, lactate, glycerol, and propionate. 

In adipose tissue, the effect of the decrease in insulin and increase in glucagon results in inhibition of lipo-genesis, inactivation of lipoprotein lipase, and activation of hormone-sensitive lipase (Chapter 25). This leads to release of increased amounts of glycerol (a substrate for gluconeogenesis in the liver) and free fatty acids, which are used by skeletal muscle and liver as their preferred metabolic fuels, so sparing glucose. 

Kidney Excretion and glu-coneogenesis Gluconeogenesis Free fatty acids, lactate, glycerol Glucose Glycerol kinase, phosphoenolpyruvate carboxy kinase... 

Gluconeogenesis Formation of glucose from precursors other than carbohydrates (especially by the liver and kidney) using amino acids from proteins, glycerol from fats, or lactate produced by muscle during anaerobic glycolysis. 

Pittner, R.A., Fears, R. and Brindley, D.N. (1985). Effects of glucocorticoids and insulin on activities of phosphatidate phosphohydrolase, tyrosine aminotransferase and glycerol kinase in isolated rat hepatocytes in relation to the control of triacyglycerol synthesis and gluconeogenesis. Biochem. J. 225 455—462. 

The interconversion of fructose-6-phosphate and fructose-1,6 bis phosphate is a control point in glycolysis and gluconeogenesis. Gluconeogenesis is a pathway which allows carbon atoms from substrates such as lactate, glycerol and some amino acids to be used for the synthesis of glucose, so it is in effect physiologically the opposite of... 

Glycerol may be picked up by liver and converted to dihydroxyacetone phosphate (DHAP) for gluconeogenesis, and the fetty adds are distributed to tissues that can use them. Free fatty acids are transported through the blood in association with serum albumin. 

Gluconeogenesis is the de novo synthesis of glucose from none carbohydrate sources. These sources (precursors) are lactic acid, glycerol and the amino acids, especially alanine, glntamine and aspartic acid (Fignre 6.22). 

Hormones can modify the concentration of precursors, particularly the lipolytic hormones (growth hormone, glucagon, adrenaline) and cortisol. The lipolytic hormones stimulate lipolysis in adipose tissue so that they increase glycerol release and the glycerol is then available for gluconeogenesis. Cortisol increases protein degradation in muscle, which increases the release of amino acids (especially glutamine and alanine) from muscle (Chapter 18). 

The main precursors of gluconeogenesis in the liver are lactate from anaerobically working muscle cells and from erythrocytes, glucogenic amino acids from the digestive tract and muscles (mainly alanine), and glycerol from adipose tissue. The kidney mainly uses amino acids for gluconeogenesis (Glu, Gin see p.328). 

The glycerol backbones from triacylglycerol breakdown are sent to the liver for use in gluconeogenesis. 

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