Effect of adding dietary L-lysine, L-threonine and L-methionine to a low gluten diet on urea synthesis in rats

Abstract

We have shown that urinary urea excretion increased in rats fed a low quality protein. The purpose of present study was to determine whether an addition of dietary limiting amino acids affected urea synthesis in rats fed a low gluten diet. Experiments were done on three groups of rats given diets containing 10% gluten, 10% gluten +0.5% L-lysine or 10% gluten+0.5% L-lysine, 0.2% L-threonine and 0.2% L-methionine for 10 d. The urinary excretion of urea, and the liver concentrations of serine and ornithine decreased with the addition of dietary L-lysine, L-threonine and L-methionine. The fractional and absolute rates of protein synthesis in tissues increased with the treatment of limiting amino acids. The activities of hepatic urea-cycle enzymes was not related to the urea excretion. These results suggest that the addition of limiting amino acids for the low gluten diet controls the protein synthesis in tissues and hepatic ornithine and decline urea synthesis.

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

“…Therefore, the changes in N-acetylglutamate synthetase activity may have controlled N-acetylglutamate concentration and been one of the factors affecting urea synthesis in this study. The activities of various urea cycle enzymes were shown to depend on the quality of dietary protein (3)(4)(5)(6)8). However, the activity of N-acetylglutamate synthetase in the liver declined with the dietary addition of limiting amino acids in the present study.…”

“…In the previous reports, we (8) also demonstrated that the fractional and absolute rates of protein synthesis increased with the addition of dietary L-lysine, Lthreonine and L-methionine to the low gluten diet, and that the higher protein synthesis in tissues of rats given the low gluten diet supplemented with dietary limiting amino acids was likely to be one of factors behind the decrease in amino acid availability and urea synthesis. Therefore, not only substrate availability but also Nacetylglutamate may limit the rate of urea synthesis when the limiting amino acids are added to a low quality protein diet.…”

“…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 the gluten diet decreased urea excretion and improved the nitrogen balance. Therefore, the purpose of the present experiments was to elucidate the mechanism by which the addition of dietary limiting amino acids to the low quality protein alters urea synthesis.…”

“…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.…”

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

“…However, many investigators have previously reported that there was an increase in urinary urea excretion without a comparable increase in the enzyme activities when the diet containing high quality protein was replaced by the isonitrogenous diet with low quality protein (3)(4)(5)(6)(7).…”