Glutamine Load Research Articles

Hepatic ketone body regulation of renal gluconeogenesis

ObjectivesDuring fasting, liver pivotally regulates blood glucose levels through glycogenolysis and gluconeogenesis. Kidney also produces glucose through gluconeogenesis. Gluconeogenic genes are transactivated by fasting, but their expression patterns are chronologically different between the two organs. We find that renal gluconeogenic gene expressions are positively correlated with the blood β-hydroxybutyrate concentration. Thus, we herein aim to investigate the regulatory mechanism and its physiological implications. MethodsGluconeogenic gene expressions in liver and kidney were examined in hyperketogenic mice such as high-fat diet (HFD)-fed and ketogenic diet-fed mice, and in hypoketogenic PPARα knockout (PPARα−/−) mice. Renal gluconeogenesis was evaluated by rise in glycemia after glutamine loading in vivo. Functional roles of β-hydroxybutyrate in the regulation of renal gluconeogenesis were investigated by metabolome analysis and RNA-seq analysis of proximal tubule cells. ResultsRenal gluconeogenic genes were transactivated concurrently with blood β-hydroxybutyrate uprise under ketogenic states, but the increase was blunted in hypoketogenic PPARα−/− mice. Administration of 1,3-butandiol, a ketone diester, transactivated renal gluconeogenic gene expression in fasted PPARα−/− mice. In addition, HFD-fed mice showed fasting hyperglycemia along with upregulated renal gluconeogenic gene expression, which was blunted in HFD-fed PPARα−/− mice. In vitro experiments and metabolome analysis in renal tubular cells showed that β-hydroxybutyrate directly promotes glucose and NH3 production through transactivating gluconeogenic genes. In addition, RNA-seq analysis revealed that β-hydroxybutyrate-induced transactivation of Pck1 was mediated by C/EBPβ. ConclusionsOur findings demonstrate that β-hydroxybutyrate mediates hepato–renal interaction to maintain homeostatic regulation of blood glucose and systemic acid-base balance through renal gluconeogenesis regulation.

An in vitro study of urea and ammonia production and transport by the intestinal tract of fed and fasted rainbow trout: responses to luminal glutamine and ammonia loading

Digestion of dietary protein in teleosts results in high ammonia levels within the intestinal chyme that may reach concentrations that are many-fold greater than blood plasma levels. We used in vitro gut sac preparations of the ammoniotelic rainbow trout (Oncorhynchus mykiss) to investigate the role of the intestine in producing and transporting ammonia and urea, with specific focus on feeding versus fasting, and on responses to loading of the lumen with 2mmol L-1 glutamine or 2mmol L-1 ammonia. Feeding increased not only ammonia production and both mucosal and serosal fluxes, but also increased urea production and serosal fluxes. Elevated urea production was accompanied by an increase in arginase activity but minimal CPS III activity, suggesting that urea may be produced by direct arginolysis. The ammonia production and serosal fluxes increased in fasted preparations with glutamine loading, indicating an ability of the intestinal tissue to deaminate glutamine and perhaps use it as an energy source. However, there was little evidence of urea production or transport resulting from the presence of glutamine. Furthermore, the intestinal tissues did not appear to convert surplus ammonia to urea as a detoxification mechanism, as urea production and serosal flux rates decreased in fed preparations, with minimal changes in fasted preparations. Nevertheless, there was indirect evidence of detoxification by another pathway, as ammonia production rate decreased with ammonia loading in fed preparations. Overall, our study suggests that intestinal tissues of rainbow trout have the ability to produce urea and detoxify ammonia, likely via arginolysis.

Alteration of ornithine metabolism leads to dominant and recessive hereditary spastic paraplegia.

Hereditary spastic paraplegias are heterogeneous neurological disorders characterized by a pyramidal syndrome with symptoms predominantly affecting the lower limbs. Some limited pyramidal involvement also occurs in patients with an autosomal recessive neurocutaneous syndrome due to ALDH18A1 mutations. ALDH18A1 encodes delta-1-pyrroline-5-carboxylate synthase (P5CS), an enzyme that catalyses the first and common step of proline and ornithine biosynthesis from glutamate. Through exome sequencing and candidate gene screening, we report two families with autosomal recessive transmission of ALDH18A1 mutations, and predominant complex hereditary spastic paraplegia with marked cognitive impairment, without any cutaneous abnormality. More interestingly, we also identified monoallelic ALDH18A1 mutations segregating in three independent families with autosomal dominant pure or complex hereditary spastic paraplegia, as well as in two sporadic patients. Low levels of plasma ornithine, citrulline, arginine and proline in four individuals from two families suggested P5CS deficiency. Glutamine loading tests in two fibroblast cultures from two related affected subjects confirmed a metabolic block at the level of P5CS in vivo. Besides expanding the clinical spectrum of ALDH18A1-related pathology, we describe mutations segregating in an autosomal dominant pattern. The latter are associated with a potential trait biomarker; we therefore suggest including amino acid chromatography in the clinico-genetic work-up of hereditary spastic paraplegia, particularly in dominant cases, as the associated phenotype is not distinct from other causative genes.

The Effects of Glutamine Loading on Strength Performance

Glutamine is purported to have beneficial effects on muscle glycogen resynthesis and immune system responses post exercise. Following a physiological stress, glutamine supplementation may sustain muscle glutamine content, increase muscle protein synthesis and attenuate protein catabolism. A resistance training stimulus often results in an elevated protein turnover and may induce glycogen depletion, therefore glutamine supplementation may augment strength training responses. PURPOSE: The purpose of this study is to determine the effects of 7 days of glutamine loading on muscular strength performance. METHODS: In a double-blind crossover study, 16 participants (mean body mass [BM] 72 ± 5.6 kg, height 178 ± 12.2 cm, age 23.5 ±2.4 yrs) performed trials of resistance training after randomly being assigned to either a seven day loading phase of glutamine supplementation (G) of 0.3 g·kg of glutamine per day mixed with calorie free fruit juice or a placebo (P) of only juice. A warm-up on both the Nautilus Leg Press (LP) and Nautilus Chest Press (CP) of 10-12 reps at 20% BM were required prior to each trial. Trials consisted of 2 sets of LP at 150% BM and 2 sets of CP at 50% BM at a 3-1-3 movement cadence to momentary muscular fatigue with 1 minute rest between sets. Blood lactate was obtained after the second set. The aforementioned trials were conducted as a baseline (B) at pre-workout and in a fatigued condition (F) immediately following a resistance training workout. A seven day washout period was required between crossover aspects of the study. Statistical analysis by ANOVA at P< .05 were applied to these data. RESULTS: The repetitions performed were significantly greater in the following trials: Chest Press; Set 1 (7.75 ± 2.8 vs 6.56 ± 2.0), Set 2 (6.88 ± 2.9 vs 5.69 ± 2.2), Leg Press; Set 1 B (18.63 ± 9.3 vs 15.81 ± 6.7), Set 2 B (14.94 ± 8.5 vs 12.56 ± 6.5), and F Set 2 (11.19 ± 5.7 vs 9.63 ± 5.5) for G vs P conditions, respectively. CONCLUSION: A seven day regiment of glutamine supplementation permits an increase in the total work load (repetitions), which may, in part, be attributed to enhanced glycogen resynthesis. Because of the acute nature of this study, it is unknown if continued glutamine supplementation in combination with resistance training would augment the normal progression of muscular strength or hypertrophy.

203 ORAL GLUTAMINE CHALLENGE – DOES IT IMPROVE REVEALING MINIMAL HEPATIC ENCEPHALOPATHY IN CIRRHOSIS?

Background and Aims: Minimal hepatic encephalopathy (MHE) is a prevalent asymptomatic condition, whose diagnosis is difficult due to the lack of a gold standard test. Oral glutamine challenge (OGC) has been found to increase blood ammonia in patients with cirrhosis which could lead to significant cognitive impairment. The aim of our study was to evaluate the value of OGC in improving the performance of psychometric tests and arterial blood ammonia for the diagnosis of MHE. Secondary we followed the risk for development of overt hepatic encephalopathy (OHE). Methods: Fifty-four patients (male/female: 34/20; mean age 59.5yrs) with cirrhosis and 13 healthy controls matched by sex and age were included. Follow-up lasted 12 months. MHE was assessed using the psychometric hepatic encephalopathy score (PHES). Arterial ammonia blood concentrations and PHES were evaluated preand post-60 minutes of a 20 g oral glutamine load. Statistical analysis used paired t-test, relative operating characteristics (ROC) and multivariate logistic regression analysis. Results: At baseline, 29 (53.7%) out of 54 patients met the criteria for MHE, while post glutamine challenge, 43 patients (79.63%) had MHE (p < 0.0001). Arterial blood ammonia levels had significantly raised after glutamine challenge in the cirrhotic patients (baseline vs post glutamine: 85.2±20.8mg/dL vs 159.82±66.01mg/dL, p < 0.0001) as compared to controls values which remained unchanged. ROC analysis showed a pathological glutamine tolerance cut-off value of 124mg/dl. For baseline arterial blood ammonia the AUROC was 0.54 (CI: 0.402–0.680, p = 0.58), with no significant change post glutamine challenge (AUROC = 0.53, CI: 0.389–0.667, p = 0.77). In the follow-up 16 patients (29.62%) developed OHE. In multivariate model, MELD score (OR = 1.5187, 95%CI: 1.0690–2.1574, P = 0.0197), but not Child Pugh class, arterial blood ammonia, esophageal varices grading, was a strong independent predictor of OHE. Conclusions: In cirrhotic patients, OGC appears to improve the performance of psychometric tests, but not arterial blood ammonia for the diagnosis of MHE. MELD score has proven to be independently related with OHE in the follow up. Acknowledgements: This work was made possible by the project ‘Doctoral Scholarships for increasing competitiveness in the medical and pharmaceutical field’ POSDRU/88/1.5/S/58965.

A capillary blood ammonia bedside test following glutamine load to improve the diagnosis of hepatic encephalopathy in cirrhosis

BackgroundHepatic encephalopathy (HE) is a frequent and severe complication of cirrhosis. A single determination of ammonia in venous blood correlates poorly with neurological symptoms. Thus, a better biological marker is needed.AimTo make a diagnosis of HE, we explored the value of ammonia in capillary blood, an equivalent to arterial blood, measured at bedside following an oral glutamine challenge.MethodsWe included 57 patients (age 56 yrs; M/F: 37/20) with cirrhosis (alcoholic = 42; MELD score 13.8 [7-29], esophageal varices = 38) and previous episodes of HE (n = 19), but without neurological deficits at time of examination, and 13 healthy controls (age 54 yrs). After psychometric tests and capillary (ear lobe) blood ammonia measurements, 20 gr of glutamine was administered orally. Tests were repeated at 60 minutes (+ blood ammonia at 30'). Minimal HE was diagnosed if values were > 1.5 SD in at least 2 psychometric tests. Follow-up lasted 12 months.ResultsThe test was well tolerated (nausea = 1; dizziness = 1). Patients showed higher values of capillary blood ammonia over time as compared to controls (0'-30'-60 minutes: 75, 117, 169 versus 52, 59, 78 umol/L, p < 0.05). At baseline, 25 patients (44%) had minimal HE, while 38 patients (67%) met the criteria for HE at 60 minutes (chi2: p < 0.01). For the diagnosis of minimal HE, using the ROC curve analysis, baseline capillary blood ammonia showed an AUC of 0.541 (CI: 0.38-0.7, p = 0.6), while at 60 minutes the AUC was 0.727 (CI: 0.58-0.87, p < 0.006). During follow-up, 18 patients (31%) developed clinical episodes of HE. At multivariate analysis, the MELD score (1.12 [1.018-1.236]), previous episodes of HE (3.2[1.069-9.58]), but not capillary blood ammonia, were independent predictors of event.ConclusionsIn patients with cirrhosis and normal neurological examination, bedside determination of ammonia in capillary blood following oral glutamine load is well tolerated and achieves a better diagnostic performance for minimal HE than basal capillary ammonia levels. However, capillary blood ammonia is a poor predictor of development of clinically overt HE.

Glutamine, arginine and the amino acid transporter Pt-CAT11 play important roles during senescence in poplar

Nitrogen (N) availability in the forest soil is extremely low and N economy has a special importance in woody plants that are able to cope with seasonal periods of growth and development over many years. Here we report on the analysis of amino acid pools and expression of key genes in the perennial species Populus trichocarpa during autumn senescence. Amino acid pools were measured throughout senescence. Expression analysis of arginine synthesis genes and cationic amino acid transporter (CAT) genes during senescence was performed. Heterologous expression in yeast mutants was performed to study Pt-CAT11 function in detail. Analysis of amino acid pools showed an increase of glutamine in leaves and an accumulation of arginine in stems during senescence. Expression of arginine biosynthesis genes suggests that arginine was preferentially synthesized from glutamine in perennial tissues. Pt-CAT11 expression increased in senescing leaves and functional characterization demonstrated that Pt-CAT11 transports glutamine. The present study established a relationship between glutamine synthesized in leaves and arginine synthesized in stems during senescence, arginine being accumulated as an N storage compound in perennial tissues such as stems. In this context, Pt-CAT11 may have a key role in N remobilization during senescence in poplar, by facilitating glutamine loading into phloem vessels.

Altered response to oral glutamine challenge as prognostic factor for overt episodes in patients with minimal hepatic encephalopathy

Background/Aims: We assessed the usefulness of oral glutamine challenge (OGC) and minimal hepatic encephalopathy in evaluating risk of overt hepatic encephalopathy in cirrhotic patients. Methods: Minimal hepatic encephalopathy (MHE) was inferred using neuro-psychological tests. Venous ammonia concentrations were measured pre- and post-60 min (NH 3-60m) of a 10 g oral glutamine load. Receiver-operating-characteristic curve analysis indicated a pathological glutamine tolerance cut-off value of NH 3-60m >128 μg/dl. Results: In healthy control subjects ( n=10) ammonia concentrations remained unchanged but increased significantly in cirrhotic patients (from 70.41±45.2 to 127.43±78.6; P<0.001). In multiple logistic regression analysis, altered OGC was related to Child-Pugh (odds ratio, OR=7.69; 95% confidence interval, CI=1.72–33.3; P<0.01) and MHE (OR=5.45; 95% CI=1.17–25.4; P<0.05). In the follow-up 11 patients (15%) developed overt hepatic encephalopathy (HE). In multivariate analysis OGC (OR=14.5; 95% CI=1.26–126.3) and MHE (OR=1.56; 95% CI=1.02–21.9) were independently related with HE in the follow-up. Patients with MHE and altered OGC showed significantly higher risk of overt HE in the follow-up (60%) than patients without MHE and normal OGC (2.8%) (Log rank test=21.60; P<0.0001). Conclusions: A pathological OGC in patients with MHE appears to be a prognostic factor for the development of overt hepatic encephalopathy, whereas a normal OGC in patients without MHE could exclude risk of overt HE.

Effect of sodium benzoate on blood ammonia response to oral glutamine challenge in cirrhotic patients: a note of caution

OBJECTIVE: The administration of sodium benzoate provides an alternative pathway for the disposal of waste nitrogen and this substance has been used to treat patients with urea cycle defects and more recently cirrhotics with hepatic encephalopathy. The aim of the study was to assess the ammonia-lowering effect of benzoate in cirrhotic patients without overt hepatic encephalopathy. METHODS: Glutamine challenge, a method to induce an increase of blood ammonia, was performed in six cirrhotics before and after 5 days of benzoate treatment (10 g/day). Number Connection Test and Posner’s Attention Test were also performed before and after benzoate treatment. RESULTS: Blood ammonia increased after the glutamine load both before (from 66 ± 12 μg/dl to 123 ± 34 μg/dl and 179 ± 53 μg/dl after 30 and 60 min, respectively; ANOVA p = 0.0004) and after benzoate treatment (from 102 ± 27 μg/dl to 185 ± 49 μg/dl and 250 ± 39 μg/dl after 30 and 60 min, respectively; ANOVA p = 0.00001). However, after benzoate treatment, the basal values (102 ± 27 vs 66 ± 12 μg/dl; p = 0.01) and peak increments of ammonia (166 ± 56 μg/dl vs 102 ± 40 μg/dl; p = 0.04) were significantly higher than before. The Number Connection test and the Posner’s test were not altered by benzoate treatment. CONCLUSIONS: Benzoate increased both the basal and postglutamine ammonia levels. These results confirm what has already been observed in experimental animals and suggest a note of caution in the use of sodium benzoate in cirrhotic patients.

Effect of sodium benzoate on blood ammonia response to oral glutamine challenge in cirrhotic patients: a note of caution.

The administration of sodium benzoate provides an alternative pathway for the disposal of waste nitrogen and this substance has been used to treat patients with urea cycle defects and more recently cirrhotics with hepatic encephalopathy. The aim of the study was to assess the ammonia-lowering effect of benzoate in cirrhotic patients without overt hepatic encephalopathy. Glutamine challenge, a method to induce an increase of blood ammonia, was performed in six cirrhotics before and after 5 days of benzoate treatment (10 microg/day). Number Connection Test and Posner's Attention Test were also performed before and after benzoate treatment. Blood ammonia increased after the glutamine load both before (from 66 +/- 12 microg/dl to 123 +/- 34 microg/dl and 179 +/- 53 microg/dl after 30 and 60 min, respectively; ANOVA p = 0.0004) and after benzoate treatment (from 102 +/- 27 microg/dl to 185 +/- 49 microg/dl and 250 +/- 39 microg/dl after 30 and 60 min, respectively; ANOVA p = 0.00001). However, after benzoate treatment, the basal values (102 +/- 27 vs 66 +/- 12 microg/dl; p = 0.01) and peak increments of ammonia (166 +/- 56 microg/dl vs 102 +/- 40 microg/dl; p = 0.04) were significantly higher than before. The Number Connection test and the Posner's test were not altered by benzoate treatment. Benzoate increased both the basal and post-glutamine ammonia levels. These results confirm what has already been observed in experimental animals and suggest a note of caution in the use of sodium benzoate in cirrhotic patients.

Effect of l-ornithine-l-aspartate on patients with and without TIPS undergoing glutamine challenge: a double blind, placebo controlled trial

BACKGROUND AND AIMAn oral glutamine load in cirrhotic patients awaiting liver transplantation was shown to cause a rise in blood ammonia and psychometric abnormalities which were reversed by hepatic transplantation....

Effect of lactitol on blood ammonia response to oral glutamine challenge in cirrhotic patients: evidence for an effect of nonabsorbable disaccharides on small intestine ammonia generation

OBJECTIVE: Nonabsorbable disaccharides are widely used to decrease blood ammonia concentration. Their principal mode of action is the modification of pH and bacterial flora in the colon. The aim of the present study was to test the hypothesis that these drugs may also reduce small intestine ammonia generation. METHODS: Eight male cirrhotics without overt hepatic encephalopathy received 20 g of glutamine in 100 ml of water. Venous samples for whole blood ammonia were taken before, 30 and 60 min after the load. Immediately after the last blood sample the patients were submitted to the following psychometric tests: number connection test, Posner’s attention test, and Sternberg paradigm. After the first glutamine load, patients were started on lactitol (initial dose 20 g, three times a day). Once two bowel movements/day were obtained and maintained for at least 5 days, oral glutamine challenge and psychometric tests were repeated. RESULTS: Ammonia increased significantly after the glutamine load (from 83 ± 13 to 164 ± 30 μg/dl at 30 min and 210 ± 29 μg/dl at 60 min; mean ±SE; p = 0.006 analysis of variance) but not after glutamine load after lactitol treatment (from 77 ± 17 to 111 ± 21 μg/dl and 142 ± 24 μg/dl; p = not significant). The peak increment (127 ± 24 vs 65 ± 18 μg/dl; p = 0.008) of ammonia elevation was significantly smaller during lactitol administration. The patients’ psychometric performance after the glutamine load did not differ significantly after lactitol treatment. CONCLUSIONS: Lactitol reduces the elevation in blood ammonia that follows oral glutamine challenge. Because enterally administered glutamine is efficiently absorbed in the jejunum and, in part, metabolized to ammonia we suggest that lactitol affects small intestine ammonia generation probably by shortening the residence time of intestinal contents.

Effect of lactitol on blood ammonia response to oral glutamine challenge in cirrhotic patients: evidence for an effect of nonabsorbable disaccharides on small intestine ammonia generation.

Nonabsorbable disaccharides are widely used to decrease blood ammonia concentration. Their principal mode of action is the modification of pH and bacterial flora in the colon. The aim of the present study was to test the hypothesis that these drugs may also reduce small intestine ammonia generation. Eight male cirrhotics without overt hepatic encephalopathy received 20 g of glutamine in 100 ml of water. Venous samples for whole blood ammonia were taken before, 30 and 60 min after the load. Immediately after the last blood sample the patients were submitted to the following psychometric tests: number connection test, Posner's attention test, and Sternberg paradigm. After the first glutamine load, patients were started on lactitol (initial dose 20 g, three times a day). Once two bowel movements/day were obtained and maintained for at least 5 days, oral glutamine challenge and psychometric tests were repeated. Ammonia increased significantly after the glutamine load (from 83 +/- 13 to 164 +/- 30 microg/dl at 30 min and 210 +/- 29 microg/dl at 60 min; mean +/- SE; p = 0.006 analysis of variance) but not after glutamine load after lactitol treatment (from 77 +/- 17 to 111 +/- 21 microg/dl and 142 +/- 24 microg/dl; p = not significant). The peak increment (127 +/- 24 vs 65 +/- 18 microg/dl; p = 0.008) of ammonia elevation was significantly smaller during lactitol administration. The patients' psychometric performance after the glutamine load did not differ significantly after lactitol treatment. Lactitol reduces the elevation in blood ammonia that follows oral glutamine challenge. Because enterally administered glutamine is efficiently absorbed in the jejunum and, in part, metabolized to ammonia we suggest that lactitol affects small intestine ammonia generation probably by shortening the residence time of intestinal contents.

An oral glutamine load enhances renal acid secretion and function

In a recent study, a small oral glutamine load acutely elevated plasma bicarbonate concentrations in healthy adults (Am J Nutr 1995;61:1058-61). The present study was designed to elucidate the renal mechanism underlying the base-generating response to L-glutamine. Accordingly, vehicle (489 mL diet soda) or vehicle plus 2 g L-glutamine (28 mg/kg body wt) was ingested and the gain in extracellular fluid volume bicarbonate was compared with renal acid elimination as either ammonium excretion or tubular acid secretion (titratable acid plus bicarbonate reabsorption). Vehicle alone, which contained 27 mmol acid, did not increase extracellular fluid volume bicarbonate over the 90-min period. In contrast, L-glutamine increased plasma bicarbonate concentration (from 25.4+/-2 to 27.9+/-1 mmol/L, P < 0.05) and extracellular fluid volume bicarbonate by an estimated 39+/-10 mmol. When added to that required to neutralize the ingested acid, the combined total for new bicarbonate generated gave an estimated 66+/-10 mmol. Surprisingly, ammonium excretion accounted for < 2% of this newly generated bicarbonate. However, acid secreted and excreted as net acid (5.2+/-4.0 mmol/90 min) as well as that coupled to enhanced bicarbonate reabsorption (76+/-20 mmol/90 min) readily accounted for the estimated base gain (81+/-24 compared with 66+/-10 mmol/90 min). Concomitant with enhanced renal acid secretion, the oral glutamine load elicited an increase in glomerular filtration rate. These results rule out a role for L-glutamine as a direct precursor of bicarbonate and instead point to an indirect role in accelerating acid secretion, apparently coupled to increased glomerular filtration rate.

Enteral Glutamine Modulates Renal Glutamine Utilization

Enteral glutamine feeding effect on renal glutamine utilization was assessed from the perspective of gamma glutamyltransferase activity-dependent cellular glutamate modulation of phosphate-dependent glutaminase. After 4 d, rats fed an elemental diet supplemented with glutamine exhibited a 21% higher kidney glutamate content and 27% reduction in ammonium excretion, both P < 0.05. Glutamine removal from plasma was depressed 62% in the glutamine-fed group (324 ± 155 vs. 780 ± 154 nmol·min-1·100 g body weight-1, P < 0.05) despite an elevated arterial plasma glutamine load delivered to the kidney. Administration of acivicin, 36 mg/kg body weight, to glutamine-fed rats inhibited gamma glutamyltransferase > 90% and decreased kidney glutamate content 42%. This reduction in kidney glutamate was associated with a 3.3-fold enhancement in both glutamine extraction (474 ± 184 to 1548 ± 255 nmol·min-1·100 g body weight-1) and ammonium excretion (295 ± 30 to 978 ± 96 nmol·min-1·100 g body weight-1), both P < 0.01. These findings are consistent with enteral glutamine regulation of renal glutamine utilization through an elevation of the cellular glutamate level.

Increased plasma bicarbonate and growth hormone after an oral glutamine load

An oral glutamine load was administered to nine healthy subjects to determine the effect on plasma glutamine, bicarbonate, and circulating growth hormone concentrations. Two grams glutamine were dissolved in a cola drink and ingested over a 20-min period 45 min after a light breakfast. Forearm venous blood samples were obtained at zero time and at 30-min intervals for 90 min and compared with time controls obtained 1 wk earlier. Eight of nine subjects responded to the oral glutamine load with an increase in plasma glutamine at 30 and 60 min before returning to the control value at 90 min. Ninety minutes after the glutamine administration load both plasma bicarbonate concentration and circulating plasma growth hormone concentration were elevated. These findings demonstrate that a surprisingly small oral glutamine load is capable of elevating alkaline reserves as well as plasma growth hormone.

Increased plasma bicarbonate and growth hormone after an oral glutamine load.

An oral glutamine load was administered to nine healthy subjects to determine the effect on plasma glutamine, bicarbonate, and circulating growth hormone concentrations. Two grams glutamine were dissolved in a cola drink and ingested over a 20-min period 45 min after a light breakfast. Forearm venous blood samples were obtained at zero time and at 30-min intervals for 90 min and compared with time controls obtained 1 wk earlier. Eight of nine subjects responded to the oral glutamine load with an increase in plasma glutamine at 30 and 60 min before returning to the control value at 90 min. Ninety minutes after the glutamine administration load both plasma bicarbonate concentration and circulating plasma growth hormone concentration were elevated. These findings demonstrate that a surprisingly small oral glutamine load is capable of elevating alkaline reserves as well as plasma growth hormone.

Arteriovenous differences for glutamine in the equine gastrointestinal tract

SUMMARY Glutamine has been shown to be an important metabolic substrate of enterocytes in many animals, including cats, dogs, hamsters, human beings, monkeys, rabbits, rats, and sheep. To determine whether glutamine is important in the metabolism of cells of the equine gastrointestinal tract, we examined transintestinal differences in glutamine concentrations in the arterial and venous circulation, and measured activity of the major glutamine catabolizing enzyme, glutaminase. Arteriovenous differences provide an index of the amount of a given substrate removed by the tissue across which the measurements are made, and commonly are expressed as a percentage of substrate removed, or percent extraction. Arteriovenous differences for glutamine were determined in 7 anesthetized adult horses (weight, 450 to 500 kg) before and after an iv glutamine infusion. The mean baseline arterial glutamine concentration (± sem) was 572 ± 24 μM; this concentration quadrupled (to 2,167 ± 135 μM, P &lt; 0.01) 1 minute after iv bolus infusion of a 17.5-g glutamine load. Baseline extraction by the portal-drained viscera was 7.5 ± 1.5%; this value increased to 18 ± 2% at 1 minute (P &lt; 0.01) and had returned to baseline values 60 minutes later. Arteriovenous differences were greatest across the jejunum (11.8 ± 1.8% in the baseline period vs 33.1 ± 3.1% at 1 minute, P &lt; 0.001), with smaller differences across the colon, suggesting that the jejunum was the more avid utilizer of glutamine. Glutaminase activity was 4.38 ± 0.16 and 4.00 ± 0.60 μmol/mg of protein/h under standard conditions in jejunal and ileal mucosa, respectively. Kinetic studies of jejunal glutaminase revealed the enzyme to have a Km of 3.81 ± 0.35 mM and a Vmax of 8.08 ± 0.54 μmol/mg of protein/h, suggesting that the small intestine of horses has a high capacity to extract and metabolize circulating glutamine.

Hepatic urea production during portal glutamine loading is larger than can be explained by ammonia or amino acid uptake

Hepatic urea production during portal glutamine loading is larger than can be explained by ammonia or amino acid uptake

Glucocorticoid and acid-base homeostasis: effects on glutamine metabolism and transport.

The amino acid glutamine serves as a major fuel, powering tubular transport processes and base generation in the kidneys of acidotic animals. Removing the adrenals limits the kidneys' response to an exogenous acid load and impairs the removal rate of glutamine from the blood. Administering glucocorticoid to adrenalectomized (ADX) rats reverses a small net release of glutamine to uptake; similarly, administering an exogenous acid load to ADX rats restores the kidneys to organs of net extraction. Glucocorticoid-induced uptake is substantially less than the filtered glutamine load in contrast to uptake across both the luminal and basolateral surfaces when filtered HCO3- is reduced. Furthermore, mitochondrial glutamine oxidation is glucocorticoid dependent with a distinct impairment exhibited by the ADX acidotic rat kidney. However, combining the effect of reduced filtered HCO3- with glucocorticoid supplementation results in a marked potentiation of glutamine uptake coupled to oxidation. These results are consistent with a proposed proximal tubule cell model in which basolateral glutamine uptake is inversely related to basolateral HCO3- efflux and coupled, in the presence of glucocorticoid, to mitochondrial oxidation. This model of glucocorticoid-induced ammoniagenesis predicts an increased renal work capacity when basolateral transport of a major metabolic fuel, glutamine, is closely coupled to its oxidative metabolism.