The liver plays a vital role in most metabolic processes. One of these processes is the detoxification of ammonia in the blood. Ammonia is a by-product of normal protein metabolism and is produced by bacteria in the intestines. When the liver is damaged, the detoxification process may be disturbed and cause rising blood ammonia levels. High levels of blood ammonia can cause problems in several organs, most notably the brain.
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The liver plays a key role in the breakdown and recycling of protein. Amino acids -- the building blocks of protein -- contain nitrogen. When a diet contains a lot of protein or not enough carbohydrates, the body metabolizes amino acids for energy. Amino acid metabolism removes the nitrogen in the form of ammonia. The liver normally converts ammonia to urea, a much less toxic compound that is then excreted by the kidneys.
Role of Muscle
Muscle tissue also plays a significant role in converting ammonia to less dangerous compounds. Unfortunately, muscle wasting often occurs as a result of liver disease. The reasons for this wasting are not entirely clear, but it probably results from a combination of malnutrition, inactivity and the disruption of the liver's normal role in making proteins. The combination of liver disease and muscle wasting causes a major decrease in the body's ability to detoxify ammonia.
Any disorder that damages liver cells -- including alcoholic cirrhosis, viral hepatitis and fatty liver disease -- can decrease the liver's ability to detoxify ammonia and lead to rising blood ammonia levels. In addition, liver disease commonly causes bleeding into the digestive tract. Bleeding in the intestines causes increased ammonia production as the bacteria in the gut digest the blood proteins.
Effects of High Ammonia Levels
The most severe effects of high ammonia levels occur in the brain. A condition called hepatic encephalopathy often accompanies serious liver disease. It is characterized by personality and behavior changes, confusion and tremors. Severe cases may lead to coma and death. While ammonia is not the only factor in liver disease that contributes to hepatic encephalopathy, it typically plays a leading role. Treatments that reduce blood ammonia levels are usually at least partially effective at improving hepatic encephalopathy symptoms.
Treating High Ammonia Levels
A protein-restricted diet is the first step in treating high ammonia levels. This is usually combined with administration of fiber supplements and laxatives to increase bowel movements and flush ammonia out of the gut. Antibiotics may be prescribed to reduce the number of bacteria in the intestine and decrease the amount of ammonia produced in the bowel. If ammonia levels remain dangerously elevated, liver transplantation may be a consideration.
- Functional Biochemistry in Health and Disease; Eric Newsholme, Ph.D. and Anthony Leech, Ph.D.; 2010
- Harrison’s Principles of Internal Medicine; Dennis L. Kasper, M.D., et al.; 2005
- American College of Gastroenterology: Hepatic Encephalopathy Guidelines