Role of N-acetylglutamate turnover in urea synthesis of rats given proteins of different quality.

The purpose of this study was to find whether the synthesis and degradation of N-acetylglutamate would affect urea synthesis when the dietary protein quality was manipulated. Experiments were done on three groups of rats given diets containing 10 g gluten, 10 g casein or 10 g whole egg protein/100 g for 10 d. The urinary excretion of urea, the liver concentrations of N-acetylglutamate and free glutamate, the liver activity of N-acetylglutamate synthetase increased with the decline in quality of dietary protein. A reverse correlation was observed between the liver N-acetylglutamate degradation and liver Nacetylglutamate concentration. N-Acetylglutamate concentration in the liver was closely correlated with the concentration of glutamate and the N-acetylglutamate synthetase activity in the liver, and excretion of urea. These results suggest that the greater synthesis and the lower degradation rate of N-acetylglutamate in the liver of rats given the lower quality of protein increase the liver concentration of N-acetylglutamate and stimulate urea synthesis.

Changes in tissue protein synthesis are involved in regulating urea synthesis in rats given proteins of different quality.

The purpose of present study was to determine whether the regulation of urea synthesis is mediated through changes in supply of amino acids by protein synthesis and whether the concentration of ammonia, or activities of amino acid catabolizing enzymes, regulate urea synthesis when the dietary protein quality is manipulated. Experiments were done on three groups of rats given diets containing 10 g gluten, 10 g casein or 10 g whole egg protein/100 g for 10 d. The urinary excretion of urea, and the liver concentrations of glutamate, serine and alanine increased with a decrease in quality of dietary protein. The fractional and absolute rates of protein synthesis in tissues declined with the decrease in quality of dietary protein quality. The ammonia concentration in plasma and liver, and activities of hepatic amino acid catabolizing enzymes was not related to urea excretion under these conditions. These results suggest that the lower protein synthesis seen in tissues of rats given the lower quality of protein is likely to be one of the factors to increasing the supply of amino acids and stimulating urea synthesis.

Role of N-acetylglutamate concentration and ornithine transport into mitochondria in urea synthesis of rats given proteins of different quality.

The purpose of this study was to find whether the concentration of N-acetylglutamate and ornithine transport into mitochondria would regulate urea synthesis when the dietary protein quality was manipulated. Experiments were done on three groups of rats given diets containing 10 g of gluten, 10 g of casein, or 10 g of whole egg protein/100 g for 10 days. The plasma concentration and urinary excretion of urea, the liver concentration and synthesis of N-acetylglutamate, the liver concentrations of glutamate and lysine, and the liver ornithine transport into mitochondria increased with the decrease in quality of dietary protein. A reverse correlation was observed between the activities of urea cycle enzymes, the plasma concentration of arginine, and urinary excretion of urea under these conditions. N-Acetylglutamate concentration and ornithine transport into mitochondria in the liver were closely correlated with the excretion of urea. These results suggest that greater N-acetylglutamate concentration and ornithine transport into isolated mitochondria in the liver of rats, given the lower quality of protein, stimulate urea synthesis and that the concentrations of glutamate and lysine in the liver are at least partly related to the hepatic N-acetylglutamate synthesis and ornithine transport, respectively.