Glycogen reserves

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. 

Six compounds have vitamin Bg activity (Figure 45-12) pyridoxine, pyridoxal, pyridoxamine, and their b -phosphates. The active coenzyme is pyridoxal 5 -phos-phate. Approximately 80% of the body s total vitamin Bg is present as pyridoxal phosphate in muscle, mostly associated with glycogen phosphorylase. This is not available in Bg deficiency but is released in starvation, when glycogen reserves become depleted, and is then available, especially in liver and kidney, to meet increased requirement for gluconeogenesis from amino acids. 

Starvation stimulates the consumption of glycogen reserves in liver... 

If food is unavailable for more than approximately 24 h, glycogen reserves in the liver will become depleted and the individual would enter a state of biochemical starvation. Progressive loss of muscle protein (wasting) would occur in order to generate sufficient glucose to maintain the metabolic activity of, in particular, the central nervous system. 

The first step in glycolysis is the phosphorylation of glucose to give the ester glucose 6-phosphate. The glucose starting material may well have come from hydrolysis of starch obtained in the diet, or by utilization of glycogen reserves. 

In muscle, the extensive glycogen reserves are exclusively used for the muscles own requirements (see p. 320). The slowly initiated protein breakdown in muscle supplies amino acids for gluconeogenesis in the liver. 

Niridazole exhibits schistosomicide and amebicidal action. The mechanism of action is not known. It seems likely that it is concentrated in the parasite organism, which causes inhibition of phosphorylase activation, which is expressed in the depletion of glycogen reserves. 

A high-carbohydrate meal leads to an elevated blood glucose concentration. The glycogen reserves within cells are filled. The ATP level rises, blocking... 

When the blood glucose level falls and the liver s glycogen reserves are also exhausted, the liver still has the capacity to synthesize glucose via gluconeogenesis from amino acids that are supplied from protein breakdown. Under starvation conditions the liver forms increasing amounts of ketone bodies (see fig. 18.7). This is due to elevated concentrations of acetyl-CoA, which favor the formation of ketone bodies. The ketone bodies are secreted and used as a source of energy by other tissues, especially those tissues like the brain that cannot catabolize fatty acids directly. 

RER > 0.9) immediately after feeding. When glycogen reserves are depleted, whole-body fuel utilization shifts almost exclusively to fat (RER = 0.8) before feeding [21, 42],... 

Timeyko, V.N. (1992). Glycogen reserve depletion in the developing eggs of Atlantic salmon under saprolegniosis (In Russian). Voprosy Ikhtiologii 32,186-190. 

Muscle pyridoxal phosphate is released into the circulation (as pyridoxal) in starvation as muscle glycogen reserves are exhausted and there is less requirement for glycogen phosphorylase activity. Under these conditions, it is potentially available for redistribution to other tissues, especially the liver and kidneys, to meet the increased requirement for gluconeogenesis from amino acids (Black et al., 1978). However, during both starvation and prolonged bed rest, there is a considerable increase in urinary excretion of 4-pyridoxic acid, suggesting that much of the vitamin Be released as a result of depletion of muscle glycogen and atrophy of muscle is not redistributed, but rather is ca-tabolized and excreted (Cobum et al., 1995). 

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