Liver Glutamine Synthetase Activity and Glutamine Levels in Blood and Tissues in Chickens Fed Various Levels of Dietary Protein

Glutamine synthetase activity in the liver and glutamine levels in the blood, liver and kidney were measured in the cockerels fed 0, 5, 20 and 40% protein diets. All the chickens gained in body weight and total urinary nitrogen excretion increased linearly with protein intake. Liver glutamine synthetase activity increased with an increase of the dietary protein level. On the other hand, plasma glutamine concentration decreased with the increase of the dietary protein level, and liver glutamine concentration also responded to the changes of dietary protein level of more than 5%. Ammonia levels in the blood and urine increased linearly with the increase of the dietary protein level. Renal ammonia concentration also responded similarly to dietary protein level of more than 5%, whereas ammonia concentration in the liver showed almost the same level except for 20 protein diet feeding. The increased activity of liver glutamine synthetase and the increased ammonia production in the high protein feeding suggest that glutamine formation is greater in the chicken fed the high protein diet than in the chicken fed the low protein diet. Nevertheless, glutamine accumulation in the blood and tissues was rather small in the chickens fed the high protein diet. Uric acid concentration in the blood, liver, kidney and urine increased in proportion to the dietary protein level, and in all the dietary protein levels used here renal uric acid level was significantly higher than hepatic uric acid level. The more active synthesis of uric acid may partly account for the low concentrations of glutamine in the blood and tissues when the high protein diet was fed to chickens, since glutamine donates two of four nitrogen atoms of uric acid.