Effect of chronic renal failure with metabolic acidosis on alanine metabolism in isolated liver cells

BACKGROUND & AIMS: Decreased ureagenesis and gluconeogenesis from alanine have been reported during chronic renal failure in rat. This study addressed the respective roles of plasma-membrane transport and intracellular metabolism in these abnormalities of alanine pathways. METHODS: In hepatocytes isolated from uremic and control rats, we investigated: (1) the influence of uremia on gluconeogenesis and ureagenesis during incubations with alanine; (2) the kinetics of alanine plasma-membrane transport; (3) the relationships between intracellular alanine concentrations and its metabolism. Plasma-membrane alanine transport was assessed after addition of alanine (2 mM) by measuring its intracellular accumulation from 0 to 10 min, in the presence of a transaminase inhibitor. Alanine metabolism was studied in perifused hepatocytes by measuring intracellular alanine concentration together with urea, glucose and lactate production in the presence of increasing concentrations of alanine (0-8 mM). RESULTS: Uremic rats showed decreased plasma bicarbonate. Uremia induced (P<0.05) a decrease in both gluconeogenesis (36%) and ureagenesis (22%). Alanine plasma-membrane transport decreased by 20% during uremia. During perifusions, uremia induced a 30-40% decrease in urea, glucose, and lactate production without modifying intracellular alanine concentration. CONCLUSIONS: In uremic rats with acidosis, hepatocyte alanine utilization was impaired at both plasma-membrane transport and intracellular transamination steps.     

Increased Production and Excretion of Urea in the Kuruma Shrimp (Marsupenaeus japonicus) Exposed to Combined Environments of Increased Ammonia and Nitrite

Marsupenaeus japonicus (6.37 ± 1.29 g) individually exposed to 9 different combined solutions of ambient ammonia (C) and nitrite (C) ammonia at 0.003 [control], 0.39, and 1.49 mmol/L combined with nitrite at 0.001 [control], 0.38, and 1.49 mmol/L in 30 ppt were examined for nitrogenous excretion accumulations of ammonia, nitrite, urea, and uric acid in tissues after 48 hours. M. japonicus exposed to 0.39 mmol/L ammonia–0.38 mmol/L nitrite displayed higher levels of urea-nitrogen (UNE) and organic-N (ONE) excretion by a factor of 2.2 and 5.7, respectively, compared with shrimp exposed only to 0.39 mmol/L ammonia. Exposure to 0.39 mmol/L ammonia–0.38 mmol/L nitrite resulted in lower levels of hemolymph uric acid (HUA), gill ammonia (GAM), gill urea (GUE), gill uric acid (GUA), hepatopancreas ammonia (HPAM), hepatopancreas urea (HPUE), and hepatopancreas uric acid (APUA), respectively, compared with shrimp exposed only to 0.39 mmol/L ammonia. We concluded that M. japonicus exposed to combined environments of ammonia and nitrite display increased nitrogen metabolism and production of urea-N and other organic-N.     

Changes in oxidative metabolism in selected tissues of the crab (Scylla serrata) in response to cadmium toxicity

Changes in oxidative metabolism were studied in hepatopancreas, muscle, and hemolymph of the edible crab Scylla serrata, exposed to a sublethal concentration (2.5 ppm) of cadmium chloride. A significant decrease in glycogen, total carbohydrates, and pyruvate and an increase in lactate levels in hepatopancreas and muscle were observed. Hemolymph sugar levels were increased in experimental crabs. An increase in phosphorylase suggested increased glycogenolysis during cadmium toxicity. The decrease in lactate dehydrogenase activity and the increase in lactate content indicated reduced mobilization of pyruvate into the citric acid cycle. Krebs cycle enzymes such as succinate dehydrogenase and malate dehydrogenase were found to be decreased, suggesting impairment of mitochondrial oxidative metabolism as a consequence of cadmium toxicity. Glucose-6-phosphate dehydrogenase activity was increased, suggesting enhanced oxidation of glucose by the HMP pathway. Cytochrome-c oxidase and Mg²⁺ ATPase activity levels decreased, indicating impaired energy synthesis during cadmium stress. Acid and alkaline phosphatase activities increased, suggesting enhanced breakdown of phosphates to release energy in view of impaired ATPase system during cadmium exposure. A significant decrease in protein and free amino acid and an increase in ammonia, urea, and glutamine levels were observed in the tissues during exposure. An increase in protease, alanine aminotransaminase, and asparate aminotransaminase suggested increased proteolysis and transamination of amino acids. The increase in glutamate dehydrogenase, AMP deaminase, and adenosine deaminase indicated increased ammonia production. The increased arginase and glutamine synthetase suggested the detoxification or mobilization of ammonia toward the production of urea and glutamine. These results suggest that cadmium affects oxidative metabolism and induces hyperammonemia, and crabs switch over their metabolic profiles toward compensatory mechanisms for the survivability in cadmium-polluted habitats.     

Protein turnover, ureagenesis and gluconeogenesis

The major processes discussed below are protein turnover (degradation and synthesis), degradation into urea, or conversion into glucose (gluconeogenesis, Figure 1). Daily protein turnover is a dynamic process characterized by a double flux of amino acids: the amino acids released by endogenous (body) protein breakdown can be reutilized and reconverted to protein synthesis, with very little loss. Daily rates of protein turnover in humans (300 to 400 g per day) are largely in excess of the level of protein intake (50 to 80 g per day). A fast growing rate, as in premature babies or in children recovering from malnutrition, leads to a high protein turnover rate and a high protein and energy requirement. Protein metabolism (synthesis and breakdown) is an energy-requiring process, dependent upon endogenous ATP supply. The contribution made by whole-body protein turnover to the resting metabolic rate is important: it represents about 20 % in adults and more in growing children. Metabolism of proteins cannot be disconnected from that of energy since energy balance influences net protein utilization, and since protein intake has an important effect on postprandial thermogenesis - more important than that of fats or carbohydrates. The metabolic need for amino acids is essentially to maintain stores of endogenous tissue proteins within an appropriate range, allowing protein homeostasis to be maintained. Thanks to a dynamic, free amino acid pool, this demand for amino acids can be continuously supplied. The size of the free amino acid pool remains limited and is regulated within narrow limits. The supply of amino acids to cover physiological needs can be derived from 3 sources: 1. Exogenous proteins that release amino acids after digestion and absorption 2. Tissue protein breakdown during protein turnover 3. De novo synthesis, including amino acids (as well as ammonia) derived from the process of urea salvage, following hydrolysis and microflora metabolism in the hind gut. When protein intake surpasses the physiological needs of amino acids, the excess amino acids are disposed of by three major processes: 1. Increased oxidation, with terminal end products such as CO? and ammonia 2. Enhanced ureagenesis i. e. synthesis of urea linked to protein oxidation eliminates the nitrogen radical 3. Gluconeogenesis, i. e. de novo synthesis of glucose. Most of the amino groups of the excess amino acids are converted into urea through the urea cycle, whereas their carbon skeletons are transformed into other intermediates, mostly glucose. This is one of the mechanisms, essential for life, developed by the body to maintain blood glucose within a narrow range, (i. e. glucose homeostasis). It includes the process of gluconeogenesis, i. e. de novo synthesis of glucose from non-glycogenic precursors; in particular certain specific amino acids (for example, alanine), as well as glycerol (derived from fat breakdown) and lactate (derived from muscles). The gluconeogenetic pathway progressively takes over when the supply of glucose from exogenous or endogenous sources (glycogenolysis) becomes insufficient. This process becomes vital during periods of metabolic stress, such as starvation.     

Whole body protein metabolism in parenterally fed patients: Glucose versus fat as the predominant energy source

The effect of altering the energy source between glucose and fat on whole body nitrogen metabolism has been investigated by randomised crossover study in six patients undergoing parenteral feeding and in a stable condition. The feeding regimen was kept constant during the 10 days of each study except that for one 5-day period the non-nitrogen energy source was glucose and for the other 5 days it was Intralipid^® with 100 g of glucose. Blood glucose and plasma insulin concentrations were significantly lower on days 2 and 5 of the high fat feed. Estimation on the same days of urinary ammonia, total nitrogen, 3-methylhistidine, and corrected excretion of urea showed only a significantly greater excretion of nitrogen on day 2 of the high fat feed. Measurements of whole body nitrogen flux made by the single dose ¹⁵N glycine technique and using both ammonia and urea as end products showed little change during the two feeding regimens. When choosing an energy source for parenteral feeding, the important factors to take into consideration are those other than the effect on protein metabolism.     

Interactions between propionate and amino acid metabolism in isolated sheep hepatocytes

The purpose of the present study was to evaluate the contribution of various substrates to glucose synthesis in isolated sheep hepatocytes, and more specifically to quantify the contribution of propionate to gluconeogenesis. Liver cells from fed sheep have a very high capacity for propionate utilization and conversion into glucose. The gluogenicity of lactate or amino acids was very low in hepatocytes from fed sheep, but was significantly increased in hepatocytes from starved animals. Amino acids such as alanine or glutamine were characterized by a substantial utilization towards ureogenesis; whereas their conversion to glucose was very low. Propionate utilization and conversion into glucose was inhibited by butyrate, ammonia and especially ethanol (by up to 80%). Ethanol promoted a striking accumulation of intracellular malate in hepatocytes incubated with propionate (reaching 14.9 mumol/g cell) and led to a depletion of phosphoenolpyruvate; ethanol inhibition could be counteracted by pyruvate. Propionate and butyrate enhanced ureogenesis from ammonia in ruminant liver cells but their effects were not additive. Propionate also elicited a marked increase in cellular concentrations of phosphoserine and serine, particularly in the presence of ammonia; such effects could influence phospholipid metabolism in the liver. These findings emphasize the contribution of propionate, compared with the other glucogenic substrates, to glucose synthesis in ruminants and point to the possibilities of modulation of the glucogenicity of propionate by various substrates which may be present in portal blood.     

Decline of Lactate in Tumor Tissue After Ketogenic Diet: In Vivo Microdialysis Study in Patients with Head and Neck Cancer

In head and neck squamous cell carcinoma (HNSCC) aerobic glycolysis is the key feature for energy supply of the tumor. Quantitative microdialysis (μD) offers an online method to measure parameters of the carbohydrate metabolism in vivo. The aim was to standardize a quantitative μD-study in patients with HNSCC and to prove if a ketogenic diet would differently influence the carbohydrate metabolism of the tumor tissue. Commercially available 100 kDa-CMA71-μD- catheters were implanted in tumor-free and in tumor tissue in patients with HNSCC for simultaneous measurements up to 5 days. The metabolic pattern and circadian rhythm of urea, glucose, lactate, and pyruvate was monitored during 24 h of western diet and subsequent up to 4 days of ketogenic diet. After 3 days of ketogenic diet the mean lactate concentration declines to a greater extent in the tumor tissue than in the tumor-free mucosa, whereas the mean glucose and pyruvate concentrations rise. The in vivo glucose metabolism of the tumor tissue is clearly influenced by nutrition. The decline of mean lactate concentration in the tumor tissue after ketogenic diet supports the hypothesis that HNSCC tumor cells might use lactate as fuel for oxidative glucose metabolism.     

Effects of lactation on circulating plasma metabolites in 'cafeteria-fed' rats

1. The effects of 'cafeteria feeding' on primiparous Wistar rats during lactation have been studied by measuring circulating levels of glucose, amino acids, lactate, urea and ammonia as well as glycogen levels in liver and muscle. 2. No significant changes in glucose levels were observed despite alterations in blood glucose compartmentation. 3. Compared with controls, the dams given the cafeteria diet had higher liver glycogen stores which were more easily mobilized at the peak of lactation. 4. Rats given the cafeteria diet showed a lower amino acid utilization than controls and adequately maintained circulating levels, as determined by the lower circulating levels of ammonia and urea. 5. No significant differences in body-weight were observed in the period studied despite increasing dam weight after weaning in the cafeteria-fed group. 6. The size of pups of cafeteria-fed dams was greater than that of controls, and the differences were marked after weaning, when the metabolic machinery of the cafeteria pup maintained high protein accretion and body build-up using fat as the main energy substrate characteristic of the preweaning stage. The controls, however, changed to greater utilization of amino acids as an energy substrate and adapted to high-protein (low-biological-quality) diets with a significantly different pattern of circulating nitrogen distribution.     

Single Sodium Pyruvate Ingestion Modifies Blood Acid-Base Status and Post-Exercise Lactate Concentration in Humans

This study examined the effect of a single sodium pyruvate ingestion on a blood acid-base status and exercise metabolism markers. Nine active, but non-specifically trained, male subjects participated in the double-blind, placebo-controlled, crossover study. One hour prior to the exercise, subjects ingested either 0.1 g·kg⁻¹ of body mass of a sodium pyruvate or placebo. The capillary blood samples were obtained at rest, 60 min after ingestion, and then three and 15 min after completing the workout protocol to analyze acid-base status and lactate, pyruvate, alanine, glucose concentrations. The pulmonary gas exchange, minute ventilation and the heart rate were measured during the exercise at a constant power output, corresponding to ~90% O₂max. The blood pH, bicarbonate and the base excess were significantly higher after sodium pyruvate ingestion than in the placebo trial. The blood lactate concentration was not different after the ingestion, but the post-exercise was significantly higher in the pyruvate trial (12.9 ± 0.9 mM) than in the placebo trial (10.6 ± 0.3 mM, p < 0.05) and remained elevated (nonsignificant) after 15 min of recovery. The blood pyruvate, alanine and glucose concentrations, as well as the overall pulmonary gas exchange during the exercise were not affected by the pyruvate ingestion. In conclusion, the sodium pyruvate ingestion one hour before workout modified the blood acid-base status and the lactate production during the exercise.     

Amino-acid-dependent, differential effects of ethanol on glucose production in rabbit kidney-cortex tubules

AIMS: The effect of ethanol on glucose synthesis in kidney-cortex tubules of control and diabetic rabbits has been investigated. METHODS: Both freshly isolated and grown in primary cultures, kidney-cortex tubules were incubated with alanine or aspartate plus lactate or glycerol plus octanoate in the absence and presence of 100 mmol/l ethanol. RESULTS: In freshly isolated renal tubules incubated in the presence of alanine plus lactate or glycerol plus octanoate, and in tubules grown in primary culture in the medium containing alanine plus lactate plus octanoate alcohol, resulted in about 30% decrease in glucose formation. A diminished glucose production in freshly isolated tubules was accompanied by: (i) a decrease in alanine utilization, (ii) an increase in lactate or glycerol consumptions and (iii) a decline in GSH:GSSG ratio. The ethanol action was not abolished by 4-methylpyrazole, an inhibitor of alcohol dehydrogenase (ADH). In view of ethanol-induced changes in gluconeogenic intermediates it is likely that in the presence of alanine plus glycerol plus octanoate ethanol causes a decline in flux through phosphoenolpyruvate carboxykinase, probably due to either an increase in intracellular content of 2-oxoglutarate, inhibitor of this key gluconeogenic enzyme and/or an enhanced flux through pyruvate kinase, as concluded from an increased lactate formation in the presence of glycerol in the incubation medium. In renal tubules grown in primary cultures in the presence of alanine plus lactate plus octanoate a decrease in GSH:GSSG ratio was accompanied by elevated generation of reactive oxygen species (ROS). Upon replacement of alanine by aspartate ethanol affected neither glucose production, substrate uptake, ROS accumulation nor GSH:GSSG ratio. CONCLUSIONS: In the presence of alanine ethanol-induced decrease in glucose production and elevation of ROS might cause a limited NADPH generation resulting in a decrease in the intracellular GSH:GSSG ratio. On the contrary, aspartate might protect against ROS generation, so intensive gluconeogenesis supports NADPH generation and in consequence high values of the intracellular GSH:GSSG ratio are maintained.     

Influence of Branched-Chain Amino Acid Supplementation on Urinary Protein Metabolite Concentrations after Swimming

Objective: The influence of branched-chain amino acid (BCAA) supplementation on urinary urea nitrogen, hydroxyproline (HP), and 3-methylhistidine (3MH) concentrations after 25 min of breast stroke exercise (65–70% maximum heart rate reserved, 65–70% HRRmax) followed by a 600 m crawl stroke competition was investigated in a double-blind, counter-balanced study.

Methods: Male university students (19–22 years old) majoring in physical education participated in the study. Based on the previous swimming time of a 600 m crawl stroke, the participants were divided into two groups: placebo (n = 9, BMI = 24.2 ± 2.1 kg/m²; 12 g of glucose/day; in capsules) and BCAA (n = 10, BMI = 22.7 ± 1.5 kg/m²; 12 g of BCAAs/day; in capsules: leucine 54%, isoleucine 19%, valine 27%) groups. The participants maintained a regular dietary intake (except the prescribed breakfast on day 15) and exercise activity at a moderate/low intensity (60–70% HRRmax, swimming and rowing, ～1.5 hour/day) during the 15-day study. A prescribed exercise program was performed on day 15. Urinary and blood samples were collected before, during, and after the prescribed exercise for the measurements of the urinary urea nitrogen, HP, and 3MH concentrations in urine, as well as the glucose, lactate, glutamine, alanine, and BCAA concentrations in plasma.

Results: Two weeks of dietary supplementation did not induce any changes in the plasma glucose and total BCAA concentrations of either group, nor in the urinary urea nitrogen, HP, and 3MH concentrations in urine. On day 15, after 25 min of breast stroke exercise and a 600 m crawl stroke competition, plasma glucose concentration decreased significantly (p < 0.05) whereas plasma lactate concentration increased significantly (p < 0.05) in both groups. The exercise program prescribed in the study did not affect urinary urea nitrogen, HP, and 3MH concentrations. Twenty hours after the competition, however, a significant increase in the concentrations of urinary urea nitrogen, HP, and 3MH was found in the placebo group (p < 0.05), but not in the BCAA group.

Conclusions: The results obtained in this study suggest that swimming induced muscle proteolysis was prevented by BCAA supplementation. The mechanism could be attributed to the availability of ammonia provided by the oxidation of supplemented BCAAs during exercise.     

Effect of carnitine on propionate metabolism in the vitamin B-12--deficient rat

Acyl-CoA thioesters are generated during the oxidation of organic acids in mammalian systems. Vitamin B-12 deficiency is associated with decreased L-methylmalonyl-CoA mutase activity, and consequent accumulation of propionyl-CoA and methylmalonyl-CoA. The formation of propionylcarnitine from propionyl-CoA and carnitine provides an alternative pathway to remove propionyl-CoA from cells. Hepatocytes isolated from vitamin B-12--deficient rats metabolized propionate (1 mM) to CO2 and glucose at only 23% and 12%, respectively, of the rates observed in hepatocytes from control animals. In contrast, no difference was seen in rates of pyruvate metabolism by hepatocytes from control and vitamin B-12--deficient rats. Addition of carnitine (10 mM) to hepatocyte incubations increased the rate of propionylcarnitine formation 10- to 20-fold without altering conversion of propionate to CO2 or glucose. The rate of propionylcarnitine formation was not affected by vitamin B-12 deficiency. When carnitine (10 mM) was added, propionylcarnitine generation represented 65-71% of total propionate utilization in hepatocytes isolated from vitamin B-12--deficient rats. Gluconeogenesis from [1-14C]pyruvate was inhibited by 1 mM propionate in hepatocytes from vitamin B-12--deficient rats. No effect of 1 mM propionate on glucose formation from pyruvate was seen using hepatocytes from control rats. Intraperitoneal administration of L-carnitine resulted in a significant increase in urinary propionylcarnitine excretion from vitamin B-12--deficient rats, but not from control animals. The results demonstrate that exogenous carnitine can significantly enhance propionyl-group utilization via the formation of acylcarnitines under the conditions of impaired acyl-CoA metabolism associated with vitamin B-12 deficiency.     

Biosynthesis of hippurate, urea and pyrimidines in the fatty liver: studies with rats fed orotic acid or a diet deficient in choline and inositol, and with genetically obese (Zucker) rats

The activities of pathways for the biosynthesis of hippurate, urea and pyrimidines in hepatocytes isolated from lean livers were compared with those from three sources of fatty liver: a) the genetically obese Zucker rat, b) Sprague-Dawley rats fed a diet deficient in choline and inositol, and c) Sprague-Dawley rats fed a diet supplemented with orotic acid. The capacity for hippurate synthesis was not significantly affected by fat accumulation, but ureagenesis from saturating ammonia and ornithine was diminished about 50% in all models when fat content rose above 12% wet wt of liver. Pyrimidine biosynthesis under these conditions was similarly diminished with fat accumulation. Ureagenesis was inhibited by sodium benzoate in hepatocytes from lean livers, but not in hepatocytes from fatty livers. Other results suggest that higher rates of ureagenesis than could be achieved with the fatty liver are required in order to demonstrate inhibition by benzoate. Incorporation of [14C]NaHCO3 into orotate was also inhibited by sodium benzoate, but in hepatocytes from fatty as well as lean livers. The metabolic basis for impairment of ureagenesis and pyrimidine biosynthesis in the fatty liver requires further study. That the capacity for hippurate synthesis was not significantly affected suggests a pathway-specific mechanism.     

Cellular energy metabolism in rats receiving diets contaminated with lindane]

Young male rats, Wistar CF strain, about 70 g body weight, were fed a well-balanced diet containing 0 (control), 60 or 240 ppm lindane. The day before the experiment, all the animals were fasted, and some of them placed in a restraint wheel forcing them to walk on during 18 hrs; another group was given an i.p. injection of 2.6 g/kg glucose 30 minutes before their sacrifice. The redox and energy potentials of liver and muscle tissues were estimated after the determination of the following compounds: lactate, pyruvate, beta-hydroxybutyrate, acetoacetate, ATP, ADP, AMP, inorganic phosphate, NADP and NADPH. No effect of lindane was observed on muscle metabolism and the 60 ppm dose was without significant effect on liver metabolism. At the 240 ppm dosage: a. Lindane ingestion increased the liver betaHOB/AcAc ratio and decreased the Lac/pyr ratio. The ATP/ADP ratio was not significantly lowered, although the ATP concentration was diminished and, conversely, the AMP and inorganic P ones were elevated; b. Whereas lindane lowered the glucose effect on the mitochondrial redox potential, it had no influence on the increasing of the ATP/ADP ratio by glucose, or on the antiketogenic effect of this sugar; c. In the animals fed the lindane-contaminated diet, muscular exercise increased the liver betaHOB/AcAc and NADPH/NADP ratios, while the lac/pyr and ATP/ADP ratios were unaltered. But blood pyruvate was increased. The following interpretation has been given. Lindane ingestion inhibits liver mitochondrial activity and increases ketogenesis. The glucose treatment results in a poor glucose utilization for energy needs in the contaminated animals and the forced muscular exercise shows that gluconeogenesis proceeds at a slower rate than in the controls. It is suggested that an increased demand in NADPH, as resulting from the induction of the microsomal enzymes by lindane, is one of the mechanisms by which the pesticide inhibits the activity of the tricarboxylic acid cycle.     

Effect of intraruminal urea administration on glucose metabolism in dairy steers.

Isotope dilution techniques were used to study steady-state glucose kinetics in four rumen-fistulated Holstein steers and to study the effect of rapid absorption of ammonia from the rumen on glucose metabolism. Steers were fed a high-concentrate diet at hourly intervals from automatic feeders. Plasma glucose specific activity curves following single intravenous injection of [2-3H]glucose were used to construct a two-compartment model of the glucose pool with inflow and outflow from compartment one. Primed continuous infusion of [2-3H]glucose was used to determine the steady-state turnover rate of glucose and to monitor changes in the rates of inflow and outflow of glucose from the glucose pool following a single dosage of urea (0.4 g/kg body weight) into the rumen. Compartment sizes of the glucose pool were 65.6 and 33.5 g for compartments 1 and 2, respectively. Glucose turnover rate during steady-state was 15.4 mg/minute/kg body weight 0.75 and transfer rate of glucose between compartments was 17.9 mg/minute/kg body weight 0.75. Concentrations of rumen ammonia-nitrogen, plasma ammonia-nitrogen and plasma urea-nitrogen were 6.1, 0.5 and 4.0 mg/100 ml, respectively, before urea dosage. Rumen ammonia-nitrogen, plasma ammonia-nitrogen increased after urea dosage and reached peak concentrations, 170.0 and 1.2 mg/100 ml, respectively, approximately 120 minutes after urea dosage. Plasma urea-nitrogen increased linearly throughout the 4-hour sampling period and reached 12.0 mg/100 ml at end of the experiment. Concentration of glucose in plasma increased from 98.2 mg/100 ml before urea dosage to 114.6 mg/100 ml at 100 minutes after urea dosage. Estimates of glucose production and utilization indicated that the increased concentration of glucose in plasma in all steers was due, at least partially, to a decrease in the rate of glucose utilization. A rapid rate of glycogenolysis which resulted in a marked increase in the plasma glucose concentration also was evident in one steer.     

Infusion of ornithine-alpha-ketoglutarate in healthy subjects: effects on protein metabolism

Infusion of ornithine-alpha-ketoglutarate (Ornicetil) has been suggested to improve nitrogen balance in trauma patients. Whether this anticatabolic effect is localised to the liver or to skeletal muscle is as yet unknown. Consequently, the splanchnic and leg exchange of amino acids, urea and ammonia were measured in seven healthy non-obese subjects in the basal state and during infusion of ornithine-alpha-ketoglutarate at a rate of 28 mg/min for 150 min. The results demonstrate a six-fold rise in arterial ornithine and an increased uptake by both splanchnic and leg tissues during infusion. The splanchnic uptake of threonine and lysine also increased, while no other alterations were seen in leg amino acid exchange. The arterial urea concentration decreased slightly (-6%, P<0.01) during the infusion in spite of an unchanged urea production from the liver. The ammonia concentration fell by 20% (P<0.05), while glycerol and ketone body concentrations did not change significantly. It is concluded that intravenous infusion of ornithine-alpha-ketoglutarate in healthy subjects does not significantly influence hepatic or skeletal muscle protein metabolism.     

The effect of NO2 on erythrocyte glucose metabolism as related to changes in redox ratio [NAD+]/[NADH].

Glucose utilization of human erythrocytes increased to approximately 2.5 times control values when exposed to a mean NO₂ concentration of 336.6 ppm for 2 hours at 37°C and pH = 7.23. The fraction of glucose utilized by the pentose phosphate pathway remained constant so that actual glucose utilized by both this pathway and by glycolysis increased in proportion to the total glucose metabolized. The rate of total lactate plus pyruvate production remained unchanged. These data suggest that NO₂ may influence several loci of erythrocyte metabolism, including accumulation of glycolytic intermediates proximal to the reaction catalyzed by glyceraldehyde-3-phosphate dehydrogenase, oxidation of NADH, NADPH, and GSH, and alteration of NADH dependent enzymes.     

Integrated analysis of glucose,lipid, and urea metabolism in patients with bladder cancer. Impact of tumor stage

OBJECTIVE: The aim of the study was to characterize the metabolic changes in non-weight-losing patients with cancer of the bladder and to investigate the effect of tumor stage.The kinetics of glucose, glycerol, and urea metabolism were assessed in 22 weight-stable patients with non-metastatic bladder cancer (tumor stage p T2, n = 14) and 10 patients with benign uterine myoma (controls). METHODS: The kinetics of glucose, glycerol, and urea metabolism were assessed by [6,6-(2)H(2)]glucose, [1,1,2,3,3-(2)H(5)]glycerol, and [(15)N(2)]urea. Plasma concentrations of glucose, glycerol, urea, lactate, free fatty acids, insulin, glucagon, cortisol, epinephrine, and norepinephrine also were determined. RESULTS: Plasma concentrations of glucose, urea, and insulin were higher in cancer patients than in controls (P < 0.05). Whereas glucose production was similar in both groups, glucose clearance was lower in patients with bladder cancer (P < 0.05). Glycerol turnover rate was comparable between groups. Whole-body urea synthesis rate was higher in the cancer group than in the control group (P < 0.05), but there was no difference in urea synthesis when calculated per kilogram of fat-free body mass. Plasma concentrations of glycerol, lactate, free fatty acids, glucagon, cortisol, epinephrine, and norepinephrine were similar in both groups. There was no difference in any parameter between patients with an early tumor stage (p < T2) and patients with a later tumor stage (p > T2). CONCLUSION: Patients with bladder cancer had a lower rate of glucose clearance than did control subjects. Lipid metabolism was not affected, whereas urea synthesis rate was elevated in cancer patients. However, when expressed per kilogram of fat-free body mass, no difference in protein breakdown could be observed. The tumor stage had no effect on glucose, lipid, or protein metabolism.     

Effects of diet forage-to-concentrate ratio and intake on energy metabolism in growing beef heifers: net nutrient metabolism by visceral tissues

Effects of diet forage-to-concentrate ratio and intake on metabolism of nutrients by portal-drained viscera (PDV), liver and kidneys were measured in seven growing beef heifers. Isonitrogenous pelleted diets containing approximately 75% alfalfa or 75% concentrate were fed every 2 h at two metabolizable energy intakes. Greater intake increased net PDV removal of glucose and urea nitrogen and net PDV release of NH3N, alpha-amino nitrogen (AAN), alanine and lactate. Lower net PDV release of NH3N, liver removal of NH3N and AAN and liver release of urea nitrogen accompanied lower N intake and digestion in heifers fed the 75% concentrate vs. the 75% alfalfa diet. Lower net PDV glucose removal resulted in greater total splanchnic glucose release when heifers were fed the 75% concentrate vs. the 75% alfalfa diet. In addition, net PDV, liver and total splanchnic release of beta-hydroxybutyrate (BOHB) were lower when heifers were fed the 75% concentrate vs. the 75% alfalfa diet. Greater tissue energy retention in heifers fed the 75% concentrate vs. the 75% alfalfa diet at equal metabolizable energy intake accompanied differences in net PDV metabolism of glucose, NH3N and BOHB and liver metabolism of nitrogenous compounds, BOHB and lactate.     

Effect of dietary protein status on glucose utilization by the pentose cycle in pig adipose tissue

We investigated the effects of three levels of dietary protein (12, 18 and 23%) on lipid metabolism in pig adipose tissue (PAT). Eight-week-old male pigs were fasted for 96 hr and then refed for the same period of time. Adipose tissue biopsy samples were obtained and incubated for 3 hr in Hanks' salts containing 5.5 mM [1-¹⁴C], [6-¹⁴C], [U-¹⁴C] and [3-³H] glucose as well as 10 mM [2-¹⁴C] acetate and pyruvate. Fatty acids, CO₂, lactate and glyceride-glycerol yields were determined. An increase in dietary protein decreased (P<.05) glucose utilization and subsequent in vitro lipogenesis in PAT. A calculation of the role of the pentose cycle (PC) revealed a capacity to provide 60 to 90% of the NADPH required to support the observed rates of de novo fatty acid synthesis when glucose was a substrate. Several algorithms used to model PC acitivity in rat adipose tissue appeared to be inadequate for PAT because of a severe lack of triose phosphate pool equilibration and because of an apparent lack of CO₂ evolvement from the Krebs' Cycle. Tritium incorporation into fatty acids from [3-³H]glucose was related to ¹⁴CO₂ production from [1-¹⁴C]glucose and may be used to estimate glucose metabolism through the PC.