Liver enzyme activities in ammonia fixation by the rat

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Abstract
Capacity to handle an ammonia load was explored in rats submitted to different experimental conditions, by means of intraportal administration of NH4Cl solution and measurement of ammonia in blood removed at various times from hepatic veins. Liver enzymes that participate in ammonia fixation (glutamine synthetase, carbamyl phosphate synthetase, ornithine transcarbamylase, arginine synthetase, arginase, and glutamic dehydrogenase) were assayed in different animals under the same conditions and results were correlated with ability to clear ammonia; ATP was determined in some of the groups. All groups showed a decreased capacity to clear ammonia from blood. In animals starved during 4 days, in those fed a protein-free diet or a diet that contained zein as a source of protein, in those chronically intoxicated with CCl4, and in those partially hepatectomized, the impaired ability could be related to a diminution of all enzymes assayed. In animals given an acute dose of CCl4 and in those administered NH4Cl solution as drinking water the defect could be explained by a decreased activity of some enzymes tested. In anemic animals and in those made hypoxic, a drop in ATP content of liver was the apparent reason of impairment. The study emphasized the primary role of ATP and of the enzymes glutamine synthetase and arginine synthetase (splitting and condensing enzymes) in removal of ammonia.