Muscle wasting is a major complication associated with cirrhosis and liver failure. Normally the liver functions to convert ammonia into urea. But with liver failure, this process does not work well leading to high levels of circulating ammonia, which is thought to contribute to muscle wasting in mammals.
A new study published in the American Journal of Physiology – Regulatory, Integrative and Comparative Physiology, explored whether birds have the same muscle wasting response to ammonia as mammals. To examine this question, they exposed muscle cell cultures from chickens and rats to either ammonium acetate or glutamine. They then measured how much myostatin was present in the muscle cells as myostatin inhibits growth. What they found was that rat muscle cells treated with ammonium acetate had increased levels of myostatin. In contrast, ammonium acetate increased levels of glutamine and the diameter of muscle cells from birds – opposite of what was observed in the rodent cells.
These findings show that birds can deal with ammonia by increasing levels of glutamine synthetase, an enzyme that converts ammonia to glutamine, which has been shown to promote muscle growth in birds by preventing increases in myostatin levels. The researchers hope that understanding how birds deal with ammonia may lead to novel therapeutics for high ammonia levels in mammals.
Stern RA, Mozdziak PE. Glutamine synthetase in avian muscle contributes to a positive myogenic response to ammonia compared with mammalian muscle. 317(1): R214-R221, 2019. https://doi.org/10.1152/ajpregu.00232.2018