Analysis of Regulatory Factors for Urea Synthesis by Isolated Perfused Rat Liver

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Abstract
Capacities for urea synthesis and amino acid patterns in the perfused livers isolated from rats fed low and high-protein diets were compared. Urea formation with ammonium chloride as the nitrogen source in perfused livers isolated from rats fed on a 70% casein diet was rapid and the efficiency of conversion of ammonia to urea was 97.9%. However, that in livers isolated from Tats fed on a 5% casein diet was much slower and the efficiency of conversion of ammonia to urea was only 36.1%. The ratios of the rate of urea formation from ammonium chloride to activity of ornithine transcarbamylase [EC 2.1.3.3] in the perfused livers of rats fed on 5 and 70% casein diets were calculated. The ratio of the former condition was much lower than that of the latter. The ratios reached nearly the same level by the addition of ornithine and N-acetylglutamate, the addition of which to the perfusate caused marked elevation of the ratios in both cases. In the perfused livers from rats fed on a 5% casein diet a considerable portion of the ammonia added to the perfusate was fixed into an amino or an amide group of amino acids such as alanine, aspartate, and glutamine. On the other hand, in the perfused livers from Tats fed on a 70% casein diet most of the ammonia added was converted to urea. The regulation of urea synthesis and the relation between anabolism and catabolism of amino acids in rat livers subjected to different dietary conditions were compared.

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