Dietary Modulation of Amino Acid Transport in Rat and Human Liver (original) (raw)
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Surgery Today, 1996
Glutamine (Gln)-supplemented total parenteral nutrition (TPN) has been shown to improve mucosal adaptation after massive small bowel resection (SBR); however, its influences on intestinal amino acid metabolism remain unknown. In this study, intestinal amino acid flux, circulating plasma aminogram, mucosal glutaminase activity and protein, and DNA content were measured 7 days after massive SBR in rats receiving either standard (Std) or Gin-supplemented TPN. Sham-operated rats and rats fed chow after enterectomy served as controls. The uptake of Gin and the release of citrulline (Cit) by the remaining intestine was significantly decreased, with reduced mucosal glutaminase activity after SBR in the Chow and Std-TPN groups. Glutamine supple. mentation resulted in significantly increased gut Gin uptake compared with Std-TPN (P < 0.01). Mucosal glutaminase activity, mucosal protein, and DNA content was also increased by Gin; however, the gut release of Cit remained unchanged (P > 0.05). The subsequent decrease in circulating arginine (Arg) in the GIn-TPN group compared with the Std-TPN group (P < 0.05) was attributed to an insufficient exogenous supply. These findings show that Gin-supplemented TPN improves mucosal growth and gut Gin uptake after SBR. However, the intestinal production of Cit, which remained low in both TPN groups, may lead to an insufficiency of ell l dogenous Arg synthesis. Thus, both Gin and Arg may be essential amino acids after SBR.
Annals of Surgery, 1993
The effect of total parenteral nutrition (TPN) on small intestinal amino acid transport activity was studied in humans. Summary Background Data Studies in humans receiving TPN indicate that a decrease in the activities of the dissacharidase enzymes occurs, but morphologic changes are minimal with only a slight decrease in villous height. Methods Surgical patients were randomized to receive TPN (n = 6) or a regular oral diet (controls, n = 7) for 1 week before abdominal surgery. Ileum (5 controls, 5 TPN) or jejunum (2 controls, 1 TPN) were obtained intraoperatively and brush-border membrane vesicles (BBMV) were prepared by magnesium aggregation/differential centrifugation. Transport of L-MeAIB (a selective system A substrate), L-glutamine, L-alanine, L-arginine, L-leucine, and D-glucose was assayed by a rapid mixing/filtration technique in the presence and absence of sodium. Results Vesicles demonstrated approximately 18-fold enrichments of enzyme markers, classic overshoots, transport into an osmotically active space, and similar 1-hour equilibrium values. TPN resulted in a 26-44% decrease in the carrier-mediated transport velocity of all substrates except glutamine across ileal BBMVs. In the one patient receiving TPN from whom jejunum was obtained, there was also a generalized decrease in nutrient transport, although glutamine was least affected. Kinetic studies of the system A transporter demonstrated that the decrease in uptake was secondary to a reduction in carrier Vm., consistent with a decrease in the number of functional carriers in the brush-border membrane. Conclusions TPN results in a decrease in brush-border amino acid and glucose transport activity. The observation that glutamine transport is not downregulated by 1 week of bowel rest may further emphasize the important metabolic role that glutamine plays as a gut fuel and in the body's response to catabolic stresses.
Journal of Animal Science, 2010
The aim of the present study was to examine the metabolic effects" of a high availability of dietary glutamic acid or glutamine. A 15% casein diet was supplemented with 7.2% glutamic acid or glutamine. The present results show that both supplementations produced only a slight modification in the circulating concentrations of glutamate. Glutamic acid supplementation noticeably enhanced (+ 19%) the arterial concentrations of glutamine, but to a lesser extent than glutamine supplementation itself (+ 54%). Large amounts of alanine were released by the digestive tract in rats fed the various diets'; this release was enhanced by glutamine (+ 33%) and, more markedly, by glutamic acid (+ 80%) supplementation. In the liver, glutamic acid and glutamine supplementation produced an increase in the catabolism of glycine, serine, and threonine that resulted in a drop of their peripheral concentrations, especially in muscles. The decrease in serine and threonine concentrations could be ascribed to the elevation of the serine(threonine)dehydratase activity (three fold), and the drop in glycine concentration seems to be connected to serine metabolism. It appears" that the administration of glutamine (but not of glutamic acid) by the oral route could be effective in increasing its" availability in peripheral tissues.
Glutamine for the gut: mystical properties or an ordinary amino acid?
Current gastroenterology reports, 1999
Glutamine is a nonessential amino acid that can be synthesized from glutamate and glutamic acid by glutamine synthetase. It is the preferred fuel for the small intestine in the rat. Results from animal studies suggest that both glutamine-supplemented parenteral nutrition and enteral diets may prevent bacterial translocation. This effect may be modulated through the preservation and augmentation of small bowel villus morphology, intestinal permeability, and intestinal immune function. The existing data from studies with humans are less compelling. What, if any, intestinal deficits actually occur during provision of exclusive parenteral nutrition remains unclear. Furthermore, the clinical significance of these changes is largely undefined. Nevertheless, glutamine and glutamine supplementation appear to be important for the normal maintenance of intestinal morphology and function, intestinal adaptation following resection, and prevention of clinical infection related to bacterial trans...
Critical Care Medicine, 2007
Objective: Glutamine and arginine are both used as nutritional supplements in critically ill patients. Although glutamine has been shown to be beneficial for the metabolically stressed patient, considerations about arginine supplementation are not unanimously determined. Our aim is to review the current knowledge on the possible interplay between glutamine and arginine generation in the stressed patient and to elaborate on whether these amino acids may function as a common denominator. Because glutamine can be given by the parenteral and enteral routes, possible different actions on the metabolic fate (e.g., generation of citrulline) with both routes are analyzed.
Nutrition Research, 2001
The objective of the present study was to determine whether the addition of glutamine or glutamic acid to an amino acid diet would interfere with growth, nitrogen balance and liver fat content following extensive enterectomy in rats. These animals were fed an isocaloric and isonitrogenous diet whose nitrogen source was a mixture of amino acids, without (Group I) or with glutamine (Group II). An additional group was not eterectomized and received a casein-based diet (Group III). Weight evolution and nitrogen balance were similar for Groups I and II. Albumin levels were lower (pϽ0.05) in Group I, in addiction to greatest amount of fat in the liver when compared to Group II and Group III. In conclusion, the animals that received diet containing glutamine had a lesser liver fat content than animals that received diet without glutamine. However, no effect on growth and nitrogen balance was observed between enterectomized groups.
American Journal of Clinical Nutrition, 2009
Background: We previously confirmed in humans the existence of a pathway of glutamine into citrulline and arginine, which is preferentially stimulated by luminally provided glutamine. However, because glutamine is unstable, we tested this pathway with a stable dipeptide of glutamine. Objectives: The objectives were to explore whether alanyl-glutamine contributes to the synthesis of arginine in humans and whether this depends on the route of administration. Design: The study was conducted under postabsorptive conditions during surgery. Sixteen patients received alanyl-[2-15 N]glutamine enterally or intravenously together with intravenously administered stable-isotope tracers of citrulline and arginine. Blood was collected from an artery, the portal vein, a hepatic vein, and the right renal vein. Arterial and venous enrichments and (tracer) net balances of alanyl-glutamine and glutamine, citrulline, and arginine across the portal-drained viscera, liver, and kidneys were determined. Parametric tests were used to test results (mean 6 SEM). P , 0.05 was considered significant. Results: Twice as much exogenous glutamine was used for the synthesis of citrulline when alanyl-glutamine was provided enterally (5.9 6 0.6%) than when provided intravenously (2.8 6 0.3%) (P , 0.01). Consequently, twice as much exogenous glutamine was used for the synthesis of arginine when alanyl-glutamine was provided enterally (5 6 0.7%) than when provided intravenously (2.4 6 0.2%) (P , 0.01). However, results at the organ level did not explain the differences due to route of administration. Conclusions: Alanyl-glutamine contributes to the de novo synthesis of arginine, especially when provided enterally. A stable-isotope study using a therapeutic dose of alanyl-glutamine is needed to investigate the clinical implications of this finding.
Clinical Nutrition, 2001
The aim of this study was to determine the metabolism and the tolerance of a new amino acid (AA) solution administered under conditions mimicking cyclical parenteral nutrition (PN) in humans. Eight healthy volunteers received peripheral PN for 10 h providing 10.5 mg N·kg−1·h−1and 2.0 kcal·kg−1·h−1(glucose-to-lipids ratio: 70/30%). For adaptation, a non-protein energy intake was increased progressively for 90 min; thereafter, AA infusion was started and maintained at a constant rate for 10 h. Plasma and urine concentrations of all the AAs were measured before, during and after the PN. For each given AA, the relation between plasma variations at the steady-state and infusion rate, plasma clearance (Cl), renal clearance (Clr), re-absorption rate (Reab) and, retention rate (Reten) were determined. The nitrogen balance (ΔN) was calculated during the PN period. The results are presented as means±sem. All plasma AA concentrations decreased during the starting period of non-protein energy intake. The plasma AA concentrations reached a steady-state within 3 h upon AA infusion, except for glycine and lysine (6 h). At the steady state, the plasma concentrations of the infused AAs were closely correlated to their infusion rate (y=−18.3+1.5 x, r2=0.92). The plasma glutamine concentration was maintained during the PN, which indicates that the solution might stimulate the de novo synthesis of this AA. When the PN was stopped, plasma levels of the AAs decreased, most of them returning to their basal levels, or significantly below for lysine (P<0.05), alanine (P<0.05), proline (P<0.01) and glutamine (P<0.05). No volunteer showed any adverse effect during the infusion period. ΔN was: 0.8±0.5 gN/10 h. Metabolic characteristics for essential AAs were: Cl<0.5 l min−1, Clr <1.5 ml·min−1Reab ⩾ 99%, Reten ⩾99% and for non-essential AAs: Cl <0.6 l·min−1except aspartate (2.8±0.3 l·min−1), Clr < 3 ml·min−1except glycine (6.8±0.7), aspartate (8.2±3.5) and histidine (8.8±1.3); Reab ⩾ 98% except glycine (95±1), aspartate (94±2) and histidine (94±1), Reten ⩾97% except histidine (94±1), glycine (95±3). These results indicate that in healthy subjects, the amounts of AAs provided by the new solution were well balanced for an intravenous administration, and so were well utilized without excessive urinary excretion. The present study provides useful metabolic parameters for a further evaluation in disease.
Clinical Science, 2008
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