Brain energy demands

Uremia results in increased permeability of the blood-brain barrier to sucrose and insulin K+ transport is enhanced whereas Na+ transport is impaired. There is an increase in brain osmolarity in acute renal failure due to the increase in urea concentrations. However, in contrast to acute renal failure, the increase in osmolarity in chronic renal failure results from the presence of idiogenic osmoles in addition to urea. CBF is increased in uremic patients but CMR02 and CMR are decreased. In the brains of rats with acute renal failure, ATP, phosphocreatine and glucose are increased whereas AMP, ADP and lactate are decreased, most probably as a result of decreased energy demands. 

Creatine (Cr) plays an important role in energy transmission and storage in cells and tissues with high energy demands. Tissues like the brain, retina, spermatozoa and cardiac and skeletal muscle contain the enzyme Cr kinase, which catalyses the interconversion of Cr and its phosphorylated analogue, phosphocreatine. The dephosphorylation of phosphocreatine yields energy, as ADP is simultaneously converted into ATP. 

Excitatory transmitters such as glutamate utilize much of the energy demand of the brain and it is well established that excessive activation of central excitatory amino acid receptors may be neurotoxic even in the presence of normal glucose and oxygen. This type of neurotoxic damage is... 

The brain has the richest blood supply of any organ in the body, the highest energy demand, and receives the largest proportion of the cardiac output. Perhaps the commonest cause of ischaemic injury to the brain in human beings is cardiac arrest... 

Mitochondriopathies associated with severe limitation of aerobic metabolism in such organs as liver, kidney, heart, and brain are probably incompatible with survival. Milder mitochondrial disorders may become clinically observable when cellular energy demand is not satisfied (e.g.. 

The brain, heart, and muscle have high energy demands and are therefore susceptible to disorders of fatty acid, ketone, or glucose metabolism. 

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