During Starvation

In addition to the effects of a low insulin/glucagon ratio, long-term changes in metabolism during starvation are induced by the corticosteroid, cortisol. 

Gortisol promotes net protein breakdown in skeletal muscle to provide amino acids as precursors for gluconeogenesis and ketone body synthesis (keto-genesis). 

Cortisol also increases the rate of triglyceride breakdown (lipolysis) in adipose tissue for these same purposes. 

The liver is again the major organ that synthesizes the principal long-term fuel, ketone bodies, acetoacetate, and 3-hydroxybutyrate, which are made from both amino acids and fatty acids. 

In prolonged fasting, triacylglycerol degradation in adipose tissue becomes maximal and sustained. 

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Inherited aldolase A deficiency and pyruvate kinase deficiency in erythrocytes cause hemolytic anemia. The exercise capacity of patients with muscle phos-phofiaictokinase deficiency is low, particularly on high-carbohydrate diets. By providing an alternative lipid fuel, eg, during starvation, when blood free fatty acids and ketone bodies are increased, work capacity is improved. 

Once formed, collagen is relatively metabolically stable. However, its breakdown is increased during starvation and various inflammatory states. Excessive production of collagen occurs in a number of conditions, eg, hepatic cirrhosis. 

Skeletal muscle can utilize ketone bodies during starvation. 

Proteolysis of muscle during starvation supplies amino acids for gluconeogenesis. 

Wolfaardt GM, JR Lawrence, RD Robarts, DE Caldwell (1995) Bioaccumulation of the herbicide diclofop in extracellular polymers and its utilization by a biofilm community during starvation. Appl Environ Microbiol 61 152-158. 

Hunt There is another side to this coin, which is what happens during starvation. There is a hierarchy of what tissues go first. 

Klebsiella pneumoniae was is Jated as a representative microorganism from produced water. The bacterium was starved in phosphate buffer salts solutions at concentrations of either 10 /ml or 10 /ml. During starvation periods of up to 24 days the bacterial cells changed in size and shape from rod-shaped, up to 2.2 ym long,... 

KETONE BODIES are generated by the liver and used by muscle and brain (after adaptation during starvation). 

Table 2.2 Approximate content of glycogen, triacylglycerol and glutamine in a normal adult male and the estimated time for which they would last, if they were the only fuel used, during two forms of physical activity and during starvation...

During starvation or hypoglycaemia, the liver partially oxidises fatty acids to form ketone bodies, which are released and oxidised by the brain, intestine and the essential muscles (see below) (Figure 7.7). 

To provide an alternative fuel to glucose during starvation. Indeed, fatty acid oxidation restricts the rate of glucose utilisation, which maintains the blood glucose level, via a regulatory mechanism known as the glucose/ fatty acid cycle (Chapter 16). 

Figure 7.24 The increase in the plasma ketone body concentration during starvation in adults and children. The ketone body comprises both acetoacetate and hydroxybutyrate.

Figure 16.2 Redprocal relationship between the changes in the concentrations of glucose and fatty adds in blood during starvation in adult humans. As the glucose concentration decreases, fatty acids are released from adipose tissue (for mechanisms see Figure 16.4). The dotted line is an estimate of what would occur if fatty acid oxidation did not inhibit glucose utilisation. Such a decrease occurs if fatty acid oxidation in muscle is decreased by specific inhibitors.

After 60 hours of starvation in lean subjects, fat utilisation (i.e. ketone bodies plus fatty acids) accounts for three-quarters of the energy expenditure (Table 16.1) a value which will rise even higher as starvation continues. Much of this increase is accounted for by hydroxybutyrate oxidation (the major ketone body) since, by 60 hours of starvation, the plasma concentration of hydroxybutyrate has increased 26-fold compared with a threefold increase in the concentration of fatty acid (the glucose concentration falls by less than 30%). By eight days of starvation there has been a sixfold increase in fatty acid concentration, whereas the concentration of hydroxybutyrate has increased about 50-fold (Table 16.2). The changes in these three major fuels in obese subjects during starvation for 38 days are shown in Figure 16.10. 

Table 16.2 Plasma concentrations of some compounds during starvation in normal lean adult males...

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