Ammonia metabolism and hepatic encephalopathy

Hepatic encephalopathy is a complex neuropsychiatric syndrome, which derives from liver failure associated with severe liver damage such as fulminant hepatitis and liver cirrhosis, and vascular abnormalities associated with liver cirrhosis. Although the cause is explained by a multifactorial theory, the accumulation of ammonia has traditionally been considered to have an important role in the pathogenesis of hepatic encephalopathy. In addition, a number of other possible mechanisms have recently proposed, including production of false neurotransmitter, activation of central gamma-aminobutyric acid-benzodiazepine receptors by ligands of endogenous origin, altered cerebral metabolism. These pathogenetic mechanisms are not necessarily exclusive. The principle of treatment is to remove or correct aggravating factors and inhibit the transfer of toxic substances such as ammonia into the bloodstream by minimizing the interaction of intestinal bacteria and nitrogen substances. Most treatments of proved value are based on the ammonia hypothesis. Ammonia metabolism is regulated by numerous factors, among which zinc has long been indicated to be involved, and its clinical application has drawn attention recently. (C) 2004 Elsevier B.V. All rights reserved.