Control of rate of glutamine metabolism in the kidney

Plasma Glutamine Changes After High-Intensity Exercise in Elite Male Swimmers

The aim of this study was to establish the pattern and time course of plasma glutamine recovery after acute, high-intensity exercise in well-trained swimmers. In Study 1, elite male swimmers (n=8) performed 15 x 100 m swimming intervals (ITS) at 70% and 95% of maximal 100m freestyle time. Resting plasma glutaminle levels were determined on a nonexercise control day (0% ITS). Venous blood samples were obtained prior to, immediately afte;, and 30, 60, 120, and 150 mini postexercise. In Study 2, the 95% ITS was repeated in elite male swuimmers (n=8), while control subjects (n=8) did not exercise, to test for any diurnal variation in plasma glutamine levels. Venous blood samples were obtained prior to and 2, 4, 6, and 8 h postexercise. In Study 1, no change was observed in plasma glutamine following the 0% (control) and 70% ITS, but following the 95% ITS glutamine decreased significantly (p < 0.01) over the recovery period. In Study 2, plasma glutamine again decreased over the recovery period in the swimmers, but no changes were observed in the controls. It was concluded that intensive swim traininlg results in postexercise decreases in plasma glutamine levels. Because glutamine has been suggested as a marker of overtraining, a need to measure glutaminle at standard times within training programs is indicated.

Glutamine, exercise and immune function. Links and possible mechanisms

Glutamine is the most abundant free amino acid in human muscle and plasma and is utilised at high rates by rapidly dividing cells, including leucocytes, to provide energy and optimal conditions for nucleotide biosynthesis. As such, it is considered to be essential for proper immune function. During various catabolic states including surgical trauma, infection, starvation and prolonged exercise, glutamine homeostasis is placed under stress. Falls in the plasma glutamine level (normal range 500 to 750 mumol/L after an overnight fast) have been reported following endurance events and prolonged exercise. These levels remain unchanged or temporarily elevated after short term, high intensity exercise. Plasma glutamine has also been reported to fall in patients with untreated diabetes mellitus, in diet-induced metabolic acidosis and in the recovery period following high intensity intermittent exercise. Common factors among all these stress states are rises in the plasma concentrations of cortisol and glucagon and an increased tissue requirement for glutamine for gluconeogenesis. It is suggested that increased gluconeogenesis and associated increases in hepatic, gut and renal glutamine uptake account for the depletion of plasma glutamine in catabolic stress states, including prolonged exercise. The short term effects of exercise on the plasma glutamine level may be cumulative, since heavy training has been shown to result in low plasma glutamine levels (< 500 mumol/L) requiring long periods of recovery. Furthermore, athletes experiencing discomfort from the overtraining syndrome exhibit lower resting levels of plasma glutamine than active healthy controls. Therefore, physical activity directly affects the availability of glutamine to the leucocytes and thus may influence immune function. The utility of plasma glutamine level as a marker of overtraining has recently been highlighted, but a consensus has not yet been reached concerning the best method of determining the level. Since injury, infection, nutritional status and acute exercise can all influence plasma glutamine level, these factors must be controlled and/or taken into consideration if plasma glutamine is to prove a useful marker of impending overtraining.

Metabolism of glucose, glutamine, long-chain fatty acids and ketone bodies by lungs of the rat

The maximum activities of some key enzymes of metabolism were studied in lungs of fed and 48-h-starved rats. The maximum activity of hexokinase in the lung is similar to that of other tissues of the body, but lower than that of phosphorylase and 6-phosphofructokinase. High activities of glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase were found in lung tissue, suggesting the importance of the pentose phosphate pathway in the lung. The activities of hexokinase and 6-phosphofructokinase were decreased whereas that of phosphorylase increased in response to starvation. Of the enzymes of the tricarboxylic acid cycle whose activities were measured, that of oxoglutarate dehydrogenase was the lowest, yet its activity (approximately 4.2 nmol/min per mg protein at 37 degrees C) was considerably greater than the flux through the cycle (0.46 nmol/min per mg protein at 37 degrees C; calculated from oxygen consumption by incubated lung slices). The activities of both oxoglutarate dehydrogenase and citrate synthase were decreased by starvation. The activities of 3-oxoacid CoA-transferase and acetoacetyl-CoA thiolase were low in lung tissue compared to those of other tissues (eg kidney, brain) and that of 3-hydroxybutyrate dehydrogenase was very low. The activity of carnitine palmitoyl transferase is higher in the lung, suggesting that fatty acids (and possibly acetoacetate) could provide acetyl-CoA as substrate for the tricarboxylic acid cycle. Very low rates of utilization of 3-hydroxybutyrate were observed during incubation of lung slices, but that of oleate was 1.2 nmol/h per mg of protein.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of glucocorticoids in regulating interorgan glutamine flow during chronic metabolic acidosis

The role of glucocorticoids in external glutamine mobilization and renal utilization was evaluated in three groups of chronically acidotic rats: sham-treated controls, adrenalectomized, and adrenalectomized supplemented with triamcinolone. Chronic acidosis was induced by administering NH4Cl in their drinking solution over a three-day period. Adrenalectomized rats were supplemented by triamcinolone at a dose of 40 micrograms/100 g/d administered by pellet implantation. Interorgan glutamine flow was evaluated in the postabsorptive state by monitoring net balances across the hindquarters, gut, liver, and kidneys. In the adrenal-intact group, acidosis increased the flow of glutamine from the hindquarters to the kidneys; splanchnic bed uptake, the major glutamine sink in nonacidosis, was eliminated by virtue of hepatic reversal from net uptake to release. Adrenalectomy, in the absence of an exogenous acid load, reversed the flow of glutamine with the kidneys releasing and the hindquarters removing glutamine. Acid loading restored hindquarter glutamine release to levels seen in the intact chronically acidotic animals; however, renal extraction is much less than that exhibited by the intact animals. As a consequence, arterial glutamine concentration rose with the overflow removed by the splanchnic bed, the major glutamine sink in adrenalectomized acidotic rats. Supplementing adrenalectomized acidotic rats with triamcinolone restored glutamine extraction to values seen in intact acidotic rats. Despite the renal extraction, the large hindquarter glutamine release led to hepatic uptake and a high rate of ureagenesis. Glucocorticoids, the release of which is enhanced in metabolic acidosis, appear essential for renal glutamine extraction while playing a lesser role in modulating hindquarter glutamine release.(ABSTRACT TRUNCATED AT 250 WORDS)

Metabolism of glucose, glutamine, long-chain fatty acids and ketone bodies by murine macrophages

Maximum activities of some key enzymes of metabolism were studied in elicited (inflammatory) macrophages of the mouse and lymph-node lymphocytes of the rat. The activity of hexokinase in the macrophage is very high, as high as that in any other major tissue of the body, and higher than that of phosphorylase or 6-phosphofructokinase, suggesting that glucose is a more important fuel than glycogen and that the pentose phosphate pathway is also important in these cells. The latter suggestion is supported by the high activities of both glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase. However, the rate of glucose utilization by 'resting' macrophages incubated in vitro is less than the 10% of the activity of 6-phosphofructokinase: this suggests that the rate of glycolysis is increased dramatically during phagocytosis or increased secretory activity. The macrophages possess higher activities of citrate synthase and oxoglutarate dehydrogenase than do lymphocytes, suggesting that the tricarboxylic acid cycle may be important in energy generation in these cells. The activity of 3-oxoacid CoA-transferase is higher in the macrophage, but that of 3-hydroxybutyrate dehydrogenase is very much lower than those in the lymphocytes. The activity of carnitine palmitoyltransferase is higher in macrophages, suggesting that fatty acids as well as acetoacetate could provide acetyl-CoA as substrate for the tricarboxylic acid cycle. No detectable rate of acetoacetate or 3-hydroxybutyrate utilization was observed during incubation of resting macrophages, but that of oleate was 1.0 nmol/h per mg of protein or about 2.2% of the activity of palmitoyltransferase. The activity of glutaminase is about 4-fold higher in macrophages than in lymphocytes, which suggests that the rate of glutamine utilization could be very high. The rate of utilization of glutamine by resting incubated macrophages was similar to that reported for rat lymphocytes, but was considerably lower than the activity of glutaminase.

Regulation of glutamine metabolism in dog kidney in vivo

In summary, we propose: that renal ammoniagenesis is regulated both by factors dependent and independent of the acid-base status, the net effect of the ammoniagenic process on the proton balance being directly related to the rate of urinary ammonium excretion; that the renal metabolism of glutamine should not be examined independently of the metabolism of other substrate physiologically taken up by the kidney; that different pathways for glutamine metabolism will change during acid-base disorders of organic or nonorganic origin; that, among the main glutamine utilizing pathways, only the GLDH pathway is influenced directly by the acid-base status; the ammoniagenic transamination pathways is regulated by substrate availability in the kidney; that the lowest ammoniagenic flux in the kidney coincides with the rate of alanine production since alanine appears to derive directly from glutamine. When this pathway is stimulated without concomitant acidosis, most of the ammonia produced is not excreted in urine but released in the renal venous blood: thus, no significant effect on the acid-base balance is produced; that glutamine is metabolized by proximal kidney tubules of acidotic dogs probably through net oxidation; that the quantitative analysis of the metabolic consequence of this process indicates that the rate of ATP turnover at this site may effectively place an upper limit to the rate of glutamine oxidation, and ammonia production by the kidney, and that this limit is nearly reached in chronically acidotic animals.

Maximum activities of some enzymes of glycolysis, the tricarboxylic acid cycle and ketone-body and glutamine utilization pathways in lymphocytes of the rat

1. The maximum activity of hexokinase in lymphocytes is similar to that of 6-phosphofructokinase, but considerably greater than that of phosphorylase, suggesting that glucose rather than glycogen is the major carbohydrate fuel for these cells. Starvation increased slightly the activities of some of the glycolytic enzymes. A local immunological challenge in vivo (a graft-versus-host reaction) increased the activities of hexokinase, 6-phosphofructokinase, pyruvate kinase and lactate dehydrogenase, confirming the importance of the glycolytic pathway in cell division. 2. The activities of the ketone-body-utilizing enzymes were lower than those of hexokinase or 6-phosphofructokinase, unlike in muscle and brain, and were not affected by starvation. It is suggested that the ketone bodies will not provide a quantitatively important alternative fuel to glucose in lymphocytes. 3. Of the enzymes of the tricarboxylic acid cycle whose activities were measured, that of oxoglutarate dehydrogenase was the lowest, yet its activity (about 4.0mumol/min per g dry wt. at 37 degrees C) was considerably greater than the flux through the cycle (0.5mumol/min per g calculated from oxygen consumption by incubated lymphocytes). The activity was decreased by starvation, but that of citrate synthase was increased by the local immunological challenge in vivo. It is suggested that the rate of the cycle would increase towards the capacity indicated by oxoglutarate dehydrogenase in proliferating lymphocytes. 4. Enzymes possibly involved in the pathway of glutamine oxidation were measured in lymphocytes, which suggests that an aminotransferase reaction(s) (probably aspartate aminotransferase) is important in the conversion of glutamate into oxoglutarate rather than glutamate dehydrogenase, and that the maximum activity of glutaminase is markedly in excess of the rate of glutamine utilization by incubated lymphocytes. The activity of glutaminase is increased by both starvation and the local immunological challenge in vivo. This last finding suggests that metabolism of glutamine via glutaminase is important in proliferating lymphocytes.