Effect of ornithine and lactate on urea synthesis in isolated hepatocytes

Ohsumi

Hayase

et al. 2011

J Nutr Sci Vitaminol

SummaryWe have shown that urinary urea excretion increased in rats given a lower quality protein. The purpose of present study was to determine whether the composition of dietary amino acids affects urea synthesis. Experiments were done on three groups of rats given diets containing a 10% gluten amino acid mix diet or 10% casein amino acid mix diet or 10% whole egg protein amino acids mix diet for 10 d. The urinary excretion of urea, the liver concentration of N -acetylglutamate, and the liver concentration of free serine, glutamic acids and alanine were greater in the group given the amino acid mix diet of lower quality. The fractional and absolute rates of protein synthesis in tissues declined with a decrease in quality of dietary amino acids. The hepatic concentration of ornithine and the activities of hepatic urea-cycle enzymes were not related to the urea excretion. These results suggest that the increased concentrations of amino acids and N -acetylglutamate seen in the liver of rats given the amino acid mix diets of lower quality are likely among the factors stimulating urea synthesis. The protein synthesis in tissues is at least partly related to hepatic concentrations of amino acids. The composition of dietary amino acids is likely to be one of the factors regulating urea synthesis when the quality of dietary protein is manipulated.

Section: Discussionmentioning

confidence: 99%

“…When substrates for urea production are present in excess, urea formation has been shown to be stimulated by adding ornithine, a urea cycle intermediate, in perfused liver ( 10,11 ) and in isolated hepatocytes ( 12 ). Thus, at least two factors other than enzyme activity-substrate and urea cycle intermediates-may regulate the rate of urea synthesis.…”

mentioning

confidence: 99%

Effect of the Quality of Dietary Amino Acids Composition on the Urea Synthesis in Rats

Ohsumi

Hayase

et al. 2011

J Nutr Sci Vitaminol

“…N-Acetylglutamate is a physiological activator of car bamylphosphate synthetase (11,26). Variation in the N-acetylglutamate concentration has correlated well with urea synthesis in intact animals (13,22,27,28) and in isolated hepatocytes (10,29).…”

Section: Discussionmentioning

confidence: 99%

Role of N-Acetylglutamate Turnover in Urea Synthesis of Rats Given Proteins of Different Quality

Journal of Nutritional Science and Vitaminology, J Nutr Sci Vit

Fukaya

Sano

et al. 2005

“…N-Acetylglutamate is a physiological activator of carbamylphosphate synthetase (13,26). Variation in the N-acetylglutamate concentration has correlated well with urea synthesis in intact animals (14,17,27,28) and in isolated hepatocytes (12,29).…”

Section: Discussionmentioning

confidence: 99%

“…Urea formation has been shown to be stimulated by adding N -acetylglutamate in perfused liver (10)(11)(12) and in isolated hepatocytes ( 13 ) when substrates for urea production were present in excess. Thus, at least two factors other than enzyme activity, substrate and N -acetylglutamate, may regulate the rate of urea synthesis.…”

mentioning

confidence: 99%

Changes in N-Acetylglutamate Are Involved in Regulating Urea Synthesis in Rats Given a Low Gluten Diet Supplemented with L-Lysine, L-Methinone and L-Threonine

Tuchiya

Shi

et al. 2009

J Nutr Sci Vitaminol

SummaryWe have shown that urinary urea excretion decreased in rats fed a low gluten diet supplemented with dietary limiting amino acids. The purpose of present study was to determine whether the addition of dietary limiting amino acids to a low gluten diet affected the synthesis and degradation of N -acetylglutamate and regulated urea synthesis. Experiments were done on two groups of rats, given diets containing 10% gluten or 10% gluten ϩ 0.5% L -lysine, 0.2% L -threonine and 0.2% L -methionine for 10 d. The urinary excretion of urea, and the liver concentration of N -acetylglutamate, and the liver activity of N -acetylglutamate synthetase decreased with the addition of dietary L -lysine, L -threonine and L -methionine. N -Acetylglutamate concentration in the liver was closely correlated with the N -acetylglutamate synthetase activity in the liver and excretion of urea. The greater degradation of N -acetylglutamate was observed in the group fed the 10% gluten ϩ L -lysine, L -threonine and L -methionine. The hepatic concentration of glutamate and plasma concentration of arginine were not related to the N -acetylglutamate concentration in the liver. These results suggest that the addition of limiting amino acids to the low gluten diet controls the synthesis and degradation of N -acetylglutamate in the liver and lowers urea synthesis. Key Words dietary limiting amino acids, urea synthesis, N -acetylglutamate synthesis, Nacetylglutamate degradation, rats Schimke ( 1 , 2 ) has suggested that the concentrations of urea-cycle intermediates were unchanged under conditions affecting the rate of urea excretion (e.g., ingestion of a high-protein diet) and concluded that the activities of various urea-cycle enzymes were regulatory factors of urea synthesis. However, many investigators have previously reported that there was an increase in urinary urea excretion without a comparable increase in the enzyme activities when a diet containing high quality protein was replaced by an isonitrogenous diet with low quality protein ( 3-6 ).We demonstrated that urinary excretion of urea increased with a 10% casein diet and still more with a 10% gluten diet as compared with a 10% whole egg protein diet ( 5 ). Gluten is known to be a lower quality protein than whole egg protein because of deficiency in lysine ( 7 ). The concentrations of threonine and sulfur amino acids in gluten are also lower than in whole egg protein. In a previous study ( 8 ), the activities of argininosuccinate synthetase and carbamylphosphate synthetase, urea cycle enzymes, were not affected by the dietary addition of L -lysine, L -threonine and L -methionine to a low gluten diet, while supplementation with these dietary limiting amino acids to a gluten diet decreased urea excretion.Substrate availability normally may limit the rate of urea synthesis ( 9 ). Urea formation has been shown to be stimulated by adding N -acetylglutamate in perfused liver ( 10-12 ) and in isolated hepatocytes ( 13 ) when substrates for urea production were present in excess. Thus, at lea...