Glucose sparing

The net effects of these actions include enhanced growth due to protein synthesis enhanced availability of fatty acids for use by skeletal muscle as an energy source and glucose sparing for the brain, which can use only this nutrient molecule as a source of energy. 

Figure 6.48 Glucose sparing effect and net glucose synthesis when fatty acids are primary fuel...

Has a mild glucose-sparing effect and is useful in the stabilization of blood sugar because it can be converted into glucose in the liver by the process of gluconeogenesis Arginine Inhibits herpes virus... 

Glucose-sparing effect of fatty acid oxidation. Note the inhibition of glucose utilization by high levels of ATP and citrate. OA, Oxaloacetate ... 

Vigorous oxidation of a monosaccharide (e.g., with dUute nitric acid) produces carboxyl groups at both ends of the chain. Thus galactose gives the sparingly soluble mucic acid glucose affords the soluble saccharic acid, which is best isolated as the sparingly soluble acid potassium salt. 

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. 

In starvation, glucose must be ptovided for the brain and erythrocytes initially, this is supphed from hver glycogen reserves. To spare glucose, muscle and other tissues reduce glucose uptake in response to lowered insuhn secretion they also oxidize fatty acids and ketone bodies preferentially to glucose. 

Cortisol-induced lipolysis not only provides substrates for gluconeogenesis (formation of glucose from noncarbohydrate sources) but it also increases the amount of free fatty acids in the blood. As a result, the fatty acids are used by muscle as a source of energy and glucose is spared for the brain to use to form energy. 

It would seem that normally the oxidation of ketone bodies would proceed largely to completion in the liver by the ketolytic mechanism. Whenever the supply of carbohydrates here is sufficiently reduced, appreciable amounts of ketones then escape oxidation and pass into the blood. When the concentration of ketones becomes sufficiently elevated, a ketonuria occurs and also some ketones will be utilized by the tissues. Such a theory would largely limit the ketolysis mechanism to the liver. It would explain the specificity of the sugars in preventing ketonuria and the discrepancy between the amount of D-glucose required to prevent ketosis and the caloric value of the fat spared. It is further supported by the demonstration that the liver is capable of exhibiting ketolysis. 

Brain, which is usually very reliant on glucose for energy, adapts in a few days of starvation to use ketone bodies as a source of energy. This spares the body some glucose, which is still essential to maintain red cell function. 

Tabernero, A., Vicario, C. and Medina, J. M. Lactate spares glucose as a metabolic fuel in neurons and astrocytes from primary culture. Neurosci. Res. 26 369-376,1996. 

Potassium-sparing diuretics are weak antihypertensives when used alone but provide an additive hypotensive effect when combined with thiazide or loop diuretics. Moreover, they counteract the potassium- and magnesiumlosing properties and perhaps glucose intolerance caused by other diuretics. 

In the brain, when ketones are metabolized to acetyl CoA, pyruvate dehydrogenase is inhibited. Glycolysis and subsequently glucose uptake in brain decreases. This important switch spares body protein (which otherwise would be catabolized to form glucose by gluconeogenesis in the liver) by allowing the brain to indirectly metabolize fetty acids as ketone bodies. 

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