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

Abstract

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.

The Skeletal Muscle Anabolic Response to Plant- versus Animal-Based Protein Consumption

“…Ultimately, higher free AA concentrations in the liver serve as a stimulus for ureagenesis, resulting in less of the dietary-derived AAs becoming available in the systemic circulation to support the postprandial increase in MPS. This notion seems to be confirmed by animal data comparing the ingestion of crystalline AA mixtures, reflecting the AA composition of casein, egg, and wheat protein (61). It was found that the ingestion of the representative wheat mixture resulted in higher free AA concentrations in the liver and subsequent higher ureagenesis than the ingestion of the representative casein and egg mixture.…”

“…Given that all mixtures were provided as free AAs, differential digestion rates could not have influenced these findings. Therefore, the observed differences in urea production are likely attributed to differences in EAA content of the different protein sources (61). In addition, recent human data by Yang et al (21) showed that the ingestion of soy protein results in higher AA oxidation rates than does whey protein ingestion.…”

Differential Responses of Blood Essential Amino Acid Levels Following Ingestion of High-Quality Plant-Based Protein Blends Compared to Whey Protein—A Double-Blind Randomized, Cross-Over, Clinical Trial

“…The blood amino acid concentrations rose significantly and peaked one to two hours after ingestion of soy, whereas milk caused a less pronounced rise in blood amino acid concentrations that occurred later [18]. Furthermore, animal models have found that ingestion of wheat protein resulted in higher free amino acid concentration in the liver than the ingestion of representative casein and egg mixtures [19]. Based on these data, we can hypothesize that the significant influx of amino acids after soy consumption, results in a greater increase of deamination in the liver and thus, those amino acids are less available in the blood for a shorter time, as compared to milk protein.…”

Differential Responses of Blood Essential Amino Acid Levels Following Ingestion of High Quality Plant-Based Protein Blends Compared to Whey Protein - A Double-Blind Randomized, Cross-Over, Clinical Trial

“…The blood amino acid concentrations rose significantly and peaked one to two hours after ingestion of soy, whereas milk caused a less pronounced rise in blood amino acid concentrations that occurred later [18]. Further, animal models have found that ingestion of wheat protein resulted in higher free amino acid concentration in the liver than the ingestion of representative casein and egg mixtures [19]. Based on this data, we can hypothesize that the significant influx of amino acids after soy consumption, results in a greater increase of deamination in the liver, and thus those amino acids are less available in the blood for a shorter time, as compared to milk protein.…”