In vivo amino acid metabolism of gut and liver during short and prolonged starvation

1996 ◽  
Vol 270 (2) ◽  
pp. G298-G306 ◽  
Author(s):  
I. de Blaauw ◽  
N. E. Deutz ◽  
M. F. Von Meyenfeldt
Keyword(s):  
Amino Acid ◽  
Membrane Transport ◽  
Protein Turnover ◽  
Amino Acid Metabolism ◽  
Acid Metabolism ◽  
Muscle Membrane ◽  
Liver Protein ◽  
Protein Loss ◽  
Prolonged Starvation

During starvation, splanchnic organs are proportionally more affected by protein loss than other organs. Amino acid membrane transport is one of the regulating mechanisms of protein turnover, but until now in vivo data were lacking. To study in vivo phenylalanine and tyrosine membrane transport and protein turnover in splanchnic organs, a primed continuous infusion of L-[2,6-3H]phenylalanine was given to control rats (postabsorptive) and after short (40 h) and prolonged (112 h) starvation. Data were analyzed using a three-compartment model previously used in muscle membrane transport studies. Inward and outward amino acid plasma-tissue membrane transport rates in both the liver and gut were upregulated after prolonged starvation. Metabolic shunting of phenylalanine and tyrosine increased in the gut but decreased to zero in the liver after prolonged starvation. In conjunction with this, gut and liver protein turnover increased after prolonged starvation. In the liver the net uptake of gluconeogenic precursors also increased, indicative for increased gluconeogenesis. The observed changes in amino acid metabolism in both splanchnic organs after prolonged starvation may reflect an adaptation of the gut and liver to nutritional deprivation and could be of benefit during refeeding.

Glucagon receptor signaling is not required for N-carbamoyl glutamate- and l-citrulline-induced ureagenesis in mice

2020 ◽  
Vol 318 (5) ◽  
pp. G912-G927
Author(s):  
Katrine D. Galsgaard ◽  
Jens Pedersen ◽  
Sasha A. S. Kjeldsen ◽  
Marie Winther-Sørensen ◽  
Elena Stojanovska ◽  
...  
Keyword(s):  
Amino Acid ◽  
Amino Acid Metabolism ◽  
Acid Metabolism ◽  
Urea Cycle ◽  
Receptor Signaling ◽  
Glucagon Receptor ◽  
Acetylglutamate Synthase

Hepatic ureagenesis is essential in amino acid metabolism and is importantly regulated by glucagon, but the exact mechanism is unclear. With the aim to identify the steps whereby glucagon both acutely and chronically regulates ureagenesis, we here show, contrary to our hypothesis, that glucagon receptor-mediated activation of ureagenesis is not required when N-acetylglutamate synthase activity and/or N-acetylglutamate levels are sufficient to activate the first step of the urea cycle in vivo.

scholarly journals Impact of habituated dietary protein intake on fasting and postprandial whole-body protein turnover and splanchnic amino acid metabolism in elderly men: a randomized, controlled, crossover trial

2020 ◽  
Vol 112 (6) ◽  
pp. 1468-1484 ◽  
Author(s):  
Grith Højfeldt ◽  
Jacob Bülow ◽  
Jakob Agergaard ◽  
Ali Asmar ◽  
Peter Schjerling ◽  
...  
Keyword(s):  
Amino Acid ◽  
Protein Turnover ◽  
Protein Intake ◽  
Amino Acid Metabolism ◽  
Acid Metabolism ◽  
High Protein ◽  
Whole Body ◽  
Body Protein ◽  
Protein Absorption ◽  
Fasted State

ABSTRACT Background Efficacy of protein absorption and subsequent amino acid utilization may be reduced in the elderly. Higher protein intakes have been suggested to counteract this. Objectives We aimed to elucidate how habituated amounts of protein intake affect the fasted state of, and the stimulatory effect of a protein-rich meal on, protein absorption, whole-body protein turnover, and splanchnic amino acid metabolism. Methods Twelve men (65–70 y) were included in a double-blinded crossover intervention study, consisting of a 20-d habituation period to a protein intake at the RDA or a high amount [1.1 g · kg lean body mass (LBM)−1 · d−1 or >2.1 g · kg LBM−1 · d−1, respectively], each followed by an experimental trial with a primed, constant infusion of D8-phenylalanine and D2-tyrosine. Arterial and hepatic venous blood samples were obtained after an overnight fast and repeatedly 4 h after a standardized meal including intrinsically labeled whey protein concentrate and calcium-caseinate proteins. Blood was analyzed for amino acid concentrations and phenylalanine and tyrosine tracer enrichments from which whole-body and splanchnic amino acid and protein kinetics were calculated. Results High (compared with the recommended amount of) protein intake resulted in a higher fasting whole-body protein turnover with a resultant mean ± SEM 0.03 ± 0.01 μmol · kg LBM−1 · min−1 lower net balance (P < 0.05), which was not rescued by the intake of a protein-dense meal. The mean ± SEM plasma protein fractional synthesis rate was 0.13 ± 0.06%/h lower (P < 0.05) after habituation to high protein. Furthermore, higher fasting and postprandial amino acid removal were observed after habituation to high protein, yielding higher urea excretion and increased phenylalanine oxidation rates (P < 0.01). Conclusions Three weeks of habituation to high protein intake (>2.1 g protein · kg LBM−1 · d−1) led to a significantly higher net protein loss in the fasted state. This was not compensated for in the 4-h postprandial period after intake of a meal high in protein. This trial was registered at clinicaltrials.gov as NCT02587156.

Renal serine production in vivo: effects of dietary manipulation of serine status

1989 ◽  
Vol 67 (9) ◽  
pp. 1058-1061 ◽  
Author(s):  
John T. Brosnan ◽  
Beatrice Hall
Keyword(s):  
Amino Acids ◽  
Blood Flow ◽  
Amino Acid ◽  
Amino Acid Metabolism ◽  
Acid Metabolism ◽  
Dietary Manipulation ◽  
In Vivo Effects ◽  
Crystalline Amino Acids ◽  
Arteriovenous Difference

Renal serine production in rats was quantitated by simultaneously measuring renal blood flow and the renal arteriovenous difference for this amino acid. The rate of synthesis was 0.24 ± 0.02 μmol∙min−1∙100 g−1 in rats fed a diet containing 12% casein. This rate was not altered by the inclusion of an additional 1% serine in the diet for 7 days or by acute infusion of serine, although both protocols increased blood serine by 50%. When rats were fed a diet in which protein was entirely replaced by crystalline amino acids the rate of renal serine production was also 0.25 ±0.05 μmol∙min−1∙100 g−1. Omission of serine or both serine and glycine from this diet did not alter the rate of renal serine synthesis. Renal serine production does not respond to the serine content of the diet.Key words: serine, glycine, kidney, amino acid metabolism.

scholarly journals Reciprocal changes in amino acid metabolism in mammary gland and liver of the lactating rat on starvation and refeeding as indicated by the tissue accumulation of α-amino[1-14C]isobutyrate

1990 ◽  
Vol 268 (3) ◽  
pp. 799-802 ◽  
Author(s):  
A E Tedstone ◽  
V Ilic ◽  
D H Williamson
Keyword(s):  
Amino Acids ◽  
Mammary Gland ◽  
Amino Acid ◽  
Amino Acid Metabolism ◽  
Acid Metabolism ◽  
Reciprocal Relationship ◽  
Nutritional State ◽  
Tissue Accumulation

Measurements of the tissue accumulation in vivo and in vitro by hepatocytes and mammary-gland acini of alpha-amino[1-14C]isobutyrate ([1-14C]AIB) were compared in virgin and lactating rats. The results indicate the existence of a reciprocal relationship between mammary gland and liver for AIB accumulation that is dependent on the lactational and the nutritional state of the rat. This suggests that amino acids are preferentially directed to the mammary gland during active lactation.

Changes in Amino Acid Metabolism in vivo with Time after Feeding

1968 ◽  
Vol 32 (12) ◽  
pp. 1440-1447 ◽  
Author(s):  
Toshizo KIMURA ◽  
Kiyoshi ASHIDA
Keyword(s):  
Amino Acid ◽  
Amino Acid Metabolism ◽  
Acid Metabolism

scholarly journals Current Therapeutics, Their Problems, and Sulfur-Containing-Amino-Acid Metabolism as a Novel Target against Infections by “Amitochondriate” Protozoan Parasites

2007 ◽  
Vol 20 (1) ◽  
pp. 164-187 ◽  
Author(s):  
Vahab Ali ◽  
Tomoyoshi Nozaki
Keyword(s):  
Drug Resistance ◽  
Amino Acid ◽  
Trichomonas Vaginalis ◽  
Amino Acid Metabolism ◽  
Acid Metabolism ◽  
Protozoan Parasites ◽  
Novel Target ◽  
Sulfur Containing

SUMMARY The “amitochondriate” protozoan parasites of humans Entamoeba histolytica, Giardia intestinalis, and Trichomonas vaginalis share many biochemical features, e.g., energy and amino acid metabolism, a spectrum of drugs for their treatment, and the occurrence of drug resistance. These parasites possess metabolic pathways that are divergent from those of their mammalian hosts and are often considered to be good targets for drug development. Sulfur-containing-amino-acid metabolism represents one such divergent metabolic pathway, namely, the cysteine biosynthetic pathway and methionine γ-lyase-mediated catabolism of sulfur-containing amino acids, which are present in T. vaginalis and E. histolytica but absent in G. intestinalis. These pathways are potentially exploitable for development of drugs against amoebiasis and trichomoniasis. For instance, l-trifluoromethionine, which is catalyzed by methionine γ-lyase and produces a toxic product, is effective against T. vaginalis and E. histolytica parasites in vitro and in vivo and may represent a good lead compound. In this review, we summarize the biology of these microaerophilic parasites, their clinical manifestation and epidemiology of disease, chemotherapeutics, the modes of action of representative drugs, and problems related to these drugs, including drug resistance. We further discuss our approach to exploit unique sulfur-containing-amino-acid metabolism, focusing on development of drugs against E. histolytica.

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