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After bolus and continuous enteral feeding of the same protein, different digestion and absorption kinetics and anabolic responses are observed. Establishing which mode of feeding has the highest anabolic potential in patients with chronic obstructive pulmonary disease (COPD) may aid in the prevention of muscle wasting, but an important confounding factor is the duration of assessments after bolus feeding. We hypothesized that the anabolic response to bolus and continuous feeding in COPD patients is comparable when methodological issues are addressed. Twenty-one older adults (12 patients with stage II–IV COPD and 9 healthy controls) were studied after intake of a fast-absorbing hydrolyzed casein protein–carbohydrate mixture either as a single bolus or as small sips (crossover design). Whole body protein synthesis (PS), breakdown (PB), net PS (PS − PB) protein efficiency (netPSPE), net protein balance (phenylalanine (PHE) intake – PHE hydroxylation) protein efficiency (netBalPE), and splanchnic PHE extraction (SPEPHE) were assessed using stable isotope tracer methodology. Bolus feeding assessments were done at 90, 95, and 99% of the calculated duration of the anabolic response. At 99%, netBalPE was higher for sip feeding than bolus feeding in both groups (P

Arginine is an important substr ate in health and disease. It is a commonly held view that arginase-1 release from injured eryt hrocytes and hepatocytes leads to arginine breakdown. However, the true relationship between plasma arginase-1 concentration and activity has remained unaddressed. Blood was sampled from patients undergoing liver resection, a known cause of hepatocyte injury and arginase-1 release, to determine arginase-1, arginine and ornithine plasma levels. Arginase activity was assessed in vitro by measuring changes in ar ginine and ornithine plasma levels during incubation of plasma and whole blood samples at 37oC. Arginase-1 plasma levels increased 8 to 10-fold during liver resection, while arginine and ornithine levels remained unchanged. In accordance with these in vivo findings, arginine and ornithine levels remained unchanged in plasma incubated at 37uC irrespective of arginase-1 concentration. In contrast, arginine plasma levels in whole blood decreased significantly during incubation, with ornithine increasing stoichiometrically. These changes were irres pective of arginase-1 plasma levels and were explained by arginase activity, present in intact erythrocytes. Next, plasma samples with 1000-fold normal arginase-1 concentrations were obtained from patients undergoing cadaveric liver transplantation. Here, a significant decrease of arginine plasma levels occurred in vivo and in vitro. In contrast with commonly held views, moderately increased arginase-1 plasma levels do not affect plasma arginine. Very high plasma arginase-1 levels are requi red to induce potential clinical relevant effects. Key words: arginase-1; arginine; cell injury

We have described recently that cancer patients have low plasma arginine concentrations, even without weight loss being present, suggesting that decreased arginine availability may be a specific feature of the presence of tumour. As arginine is important in post-operative repair, we hypothesized that abnormalities in arginine metabolism in cancer lead to an aberrant post-operative response in arginine and NO metabolism. To investigate this, we studied post-operative alterations in arginine and NO production and the acute-phase response in MCA (methylcholanthrene) sarcoma-bearing mice. Controls, mice with small MCA tumours (15% of carcass weight) were studied, either with or without undergoing laparotomy. The stable isotopes L-[guanidino-(15)N(2)-(2)H(2)]arginine and L-[ureido-(15)N]citrulline were used to study whole-body arginine and NO production rates. SAP (serum amyloid P component) concentrations were measured to assess the acute-phase response. Significance was tested using Mann-Whitney U test. In healthy FVB mice, laparotomy significantly increased whole-body arginine production (from 42+/-3 to 54+/-3 nmol x 10 g(-1) of carcass weight x min(-1)), NO production (from 1.1+/-0.1 to 1.4+/-0.2 nmol x 10 g(-1) of carcass weight x min(-1)) and levels of SAP (from 4+/-1 to 115+/-23 ng/ml), whereas in all MCA tumour-bearing mice baseline values of arginine metabolism and SAP concentration were already elevated and the response to laparotomy was absent. In conclusion, MCA tumour-bearing mice had a disturbed post-operative metabolic response, as evidenced by attenuated post-operative arginine and NO production, concomitant with an attenuated acute-phase response. This indicates that altered arginine metabolism may be an important characteristic of the metabolic changes in cancer.

Although glucose and protein metabolism have been investigated extensively in experimental models of hypodynamic sepsis, relatively little information is available regarding the compensated stage of sepsis. We investigated interorgan amino acid and glucose metabolism in a porcine model of compensated hyperdynamic sepsis. Fasting catheterized pigs received endotoxin (Escherichia coli lipopolysaccharide; 3µg·h-1·kg-1; intravenous) or saline (controls) and volume resuscitation over 24h to reproduce hyperdynamic sepsis. Primed-constant infusions of p-aminohippurate and 3H-labelled isotopes were used to measure glucose, amino acid and protein metabolism across the portal-drained viscera, liver and hindquarters (to represent muscle) at 0 and 24h of endotoxaemia. Whole-body protein and glucose flux were increased during hyperdynamic compensated sepsis. In endotoxaemic pigs, visceral protein was conserved, and hindquarter protein breakdown exceeded the increase in liver protein synthesis, resulting in net whole-body protein loss. Endotoxaemia increased hindquarter and visceral glycolysis and branched-chain amino acid transamination. The rate of efflux of glutamine and alanine from the hindquarters was higher than anticipated from protein breakdown, indicating de novo synthesis of these amino acids during endotoxaemia. In addition to the hindquarters, the portal-drained viscera provided substantial gluconeogenic amino acids and lactate to the liver. Although increased liver glutamate release constitutes an important nitrogen-sparing mechanism and carbon skeletons are effectively being cycled in glucose, net body protein is lost through increased ureagenesis during the hyperdynamic stage of sepsis. Specific amino acid requirements may develop in compensated hyperdynamic sepsis that is characterized by maintained organ perfusion and increased substrate utilization at the expense of body protein.

It is assumed that the outcome of the lactulose/rhamnose gut permeability test is not influenced by pre- or post-absorptive factors. The aim of our study was to investigate the role of a pre-absorptive factor, i.e. small-intestinal transit, and a post-absorptive factor, i.e. renal clearance. Ten healthy male subjects were studied. Urinary lactulose and rhamnose excretion was measured after intraduodenal administration of lactulose and rhamnose following induction of increased intestinal permeability using chenodeoxycholic acid (chenodiol), in the absence and in the presence of accelerated intestinal transit. Urinary sugar excretion was measured after intravenous administration of either a regular dose (50 mg/50 mg) or a high dose (250 mg/250 mg) of lactulose/rhamnose. The intraduodenal experiments showed that a combination of accelerated small-bowel transit and increased permeability did not lead to significant differences in the recovery of lactulose (P = 0.647) or rhamnose (P = 0.889), or in the lactulose/rhamnose ratio, compared with those under conditions of increased permeability alone (P = 0.68). However, lactulose recovery was significantly lower (P = 0.025) after intravenous administration of a high dose of the sugars. There was no significant difference in urinary rhamnose recovery (P = 0.575) between the high and the regular doses. This resulted in a significantly lower lactulose/rhamnose ratio (P = 0.021) after intravenous administration of a high dose, compared with a regular dose, of the sugars. In conclusion, the assumption that post-absorptive processes do not influence the outcome of the lactulose/rhamnose permeability test appears not to be valid.

1.During infusion of [5-15N]glutamine in patients with gastrointestinal cancer we unexpectedly observed a gradual decrease in time of the appearance rate (Ra) of glutamine in plasma. Here we investigate whether the failure to achieve a plateau isotopic enrichment in plasma is, among other factors, due to incomplete equilibration of the glutamine tracer with the large intramuscular free glutamine pool. 2.Plasma and intramuscular glutamine enrichment were measured during 6–11 ;h infusions of L-[5-15N]glutamine and L-[1-13C]glutamine in post-absorptive patients admitted to hospital for elective abdominal surgery. L-[1-13C]Leucine and L-[ring-2H5]phenylalanine were infused to measure the proportion of glutamine appearing in plasma directly due to its release from protein. 3.The glutamine tracer entered muscle, but the rise in intramuscular glutamine enrichment was small, presumably as a result of the enormous size of the intramuscular glutamine pool and the limited speed of entry of glutamine into muscle. In each patient the intramuscular glutamine enrichment was lower than that in plasma (P < 0.001), and both increased with tracer infusion time (P < 0.001), indicating incomplete equilibration of the glutamine tracer. 4.A comparison of the results obtained by the two glutamine tracers indicated that recycling of the nitrogen label contributed to about 15% of the decrease in Ra. 5.There was a gradual reduction in the glutamine release from proteolysis, which contributed to 16–21% of the decline in Ra. 6.We conclude that slow equilibration of the glutamine tracer with the large muscle glutamine pool significantly contributes to the absence of isotopic steady state. Consequently, the appearance rate of glutamine in plasma measured during short tracer infusion periods (hours) considerably overestimates the whole-body glutamine flux.

Muscle protein and amino acid turnover in rats in vivo: effects of short-term and prolonged starvation.de Blaauw I, Deutz NE, von Meyenfeldt MF.Department of Surgery, Fac II, University of Limburg, Maastricht, The Netherlands.1. Protein loss in muscle can be caused by decreased protein synthesis, increased breakdown or both. In small animals the tracer incorporation technique is mostly used to measure protein synthesis, but for degradation measurements in vitro or ex vivo settings are required. In human and large animal studies the arteriovenous dilution technique is used because it enables the measurement of synthesis and breakdown rates simultaneously. The applicability in small animals has not yet been proven. We used a starvation model to compare both techniques. 2. A primed constant infusion of L-[2,6-(3H)]phenylalanine was given to male Lewis rats after 16, 40, 64 and 112 h starvation. Protein synthesis rates of the gastrocnemius muscle were measured by the incorporation technique and compared with hindquarter protein turnover calculated in a two- and three-compartment arteriovenous dilution model. 3. Whole-body phenylalanine rate of appearance decreased from 456 +/- 32 after 16 h to 334 +/- 34 (nmol min-1 100 g-1 body weight) after 112 h starvation. Protein synthesis rates of the gastrocnemius muscle measured by the tracer incorporation technique decreased from 3.6 +/- 0.4 after 16 h starvation to 2.2 +/- 0.3 after 64 h starvation and 1.8 +/- 0.4 (%/day) after 112 h starvation. Hindquarter protein breakdown, calculated with the tracer dilution model, increased after 112 h starvation from 28 +/- 12 to 77 +/- 15 nmol min-1 100 g-1 body weight. Using the tracer dilution model, however, the calculated protein synthesis rate across the hindquarter also increased after prolonged starvation (29 +/- 7 and 68 +/- 16 nmol min-1 100 g-1 body weight after 16 and 112 h respectively). In conjunction with this, calculated bidirectional membrane transport rates were also enhanced. Using valine and glutamine as tracers, the enhanced amino acid turnover rates were confirmed. 4. In conclusion, our results show that during short periods of starvation both methods give similar results. After prolonged starvation, however, an opposite change in disappearance rate and protein synthesis rate was observed. Assumptions made to calculate protein turnover using the arteriovenous dilution model may account for the discrepancy and care must be taken with the interpretation when using only one model in anaesthetized small animals.

1. It has recently been suggested that glutamine may be a conditionally essential nutrient rather than a non-essential amino acid. Therefore, administration of methionine sulphoximine was used to create a model of decreased arterial glutamine concentrations for 4 days. Glutamine consumption in portal-drained viscera and liver was measured after an overnight fast by determining fluxes and intracellular concentrations in normal rats, methionine sulphoximine-treated rats and pair-fed controls. Moreover, fluxes and intracellular concentrations of several other amino acids and ammonia and production of urea by the liver were determined concomitantly. 2. Methionine sulphoximine treatment for 4 days resulted in a 50% decrease in arterial glutamine concentration. Although the glutamine consumption and the intracellular glutamine concentration of the intestine were reduced by 50% at day 4, no changes in intestinal amino acid and ammonia metabolism were observed. 3. In the liver, glutamine consumption was reduced and ammonia uptake was increased, but urea synthesis was not changed. The decreased intracellular glutamine, glutamate, aspartate and ammonia concentrations coincided with a substantial reduction in liver branched-chain amino acid production. 4. These results suggest that reduced intestinal glutamine uptake does not induce marked changes in intestinal amino acid metabolism. The decreased liver branched-chain amino acid production suggests a reduction in the net liver protein degradation rate during methionine sulphoximine treatment.

1. After operation, changes in nitrogen metabolism occur. Although increased flux of amino acids from peripheral to splanchnic organs after operation has been described, substrate utilization by the individual organs in the splanchnic area is less well characterized. We were specifically interested in substrate flux across the spleen as it is an organ with important immunological functions. 2. Therefore, hindquarter, gut, spleen and liver fluxes of amino acids, ammonia, glucose, lactate and blood gases were measured for 4 days after a standard operation in pigs. In a separate control group, fluxes were measured 2–3 weeks after this operation and these values were assumed to represent the normal situation. 3. One day after operation, the hindquarter effluxes of glutamine, alanine and several essential amino acids were increased (P 4. The experiments show that after operation in the pig, amino acid flow is from peripheral tissue to liver, probably for gluconeogenesis. The increased postoperative splenic metabolism possibly represents an indication of increased substrate utilization by the immune system.