Parameters Of Protein Metabolism Research Articles

Low-carbohydrate, high-protein diets revisited

There has been continued interest in the physiological, nutritional and clinical aspects of low-carbohydrate diets. This review will discuss the effects on appetite regulation, metabolic parameters, body weight and body composition, the role of glycemic index and glycemic load, as well as long-term outcomes. Low-carbohydrate, high-protein diets appear to improve satiety through their actions on measures of adiposity and gut peptides that influence appetite and caloric intake. Specific macronutrients such as low glycemic index carbohydrates and dietary protein impact appetite, calorie intake and metabolic parameters independent of weight loss. Long-term data, however, continue to support that total weight loss among low-carbohydrate dieters is not significantly different from low-fat dieters. The long-term safety of low-carbohydrate, high-protein diets on cardiovascular disease risk remains undetermined. Low-carbohydrate, high-protein diets may be an effective choice for weight loss, enhanced satiety and improved metabolic parameters.

Nutritional modulation of protein metabolism after gastrointestinal surgery

The metabolic response to surgery includes alterations in protein metabolism, resulting in a net loss of proteins. Protein hypercatabolism is considered an unavoidable consequence of injury, and an important source of morbidity and mortality. Our purpose was to determine the effect of nutrition on protein metabolism following gastrointestinal surgery, and to elucidate whether postoperative protein loss can be prevented with adequate nutritional support. Patients who had undergone gastrointestinal surgery were given four different parenteral nutritions with increasing glucose, lipid and amino acid content during the 7 days following surgery. Nitrogen balance, protein synthesis and protein breakdown were determined using in vivo stable isotope labelling. Other metabolites (3-methylhistidine, creatinine, urea, cortisol, glucose, insulin, amino acids and C-reactive protein) were measured. A nutrition-dependent alteration of protein metabolism was found in response to surgical injury. Nutrition modified nitrogen balance, whole-body protein breakdown and, to a lesser extent, whole-body protein synthesis and muscle protein breakdown. The low-energy parenteral nutrition without amino acids produced a negative nitrogen balance (postoperative day 7=-0.381 g protein kg(-1)day(-1)) and important alterations in postoperative protein metabolism that did not normalize during the study period (day 7 protein synthesis=239% and protein breakdown 217% vs preoperative). Patients receiving the two low energy parenteral nutritions containing amino acids had a less negative nitrogen balance (day 7=-0.011 and -0.133 g protein kg(-1)day(-1)) and a transient increase in protein metabolism. The complete parenteral nutrition maintained, during all studied days, protein metabolism parameters within the preoperative reference range (synthesis day 2=92%, day 4=110% day 7=79%; breakdown day 2=85%, day 4=80%, day 7=76% vs preoperative) and a positive nitrogen balance (day 2=+0.0387, day 4=+0.578 and day 7=+0.227 g protein kg(-1)day(-1)). Complete nutritional support can prevent protein loss after gastrointestinal surgery and maintain protein metabolism without alterations.

Raw and extruded field beans (Vicia faba var. minor) as alternative protein sources in heavy lamb diets

The possible risk connected to GMO use in animal breeding leads to reconsider animal production processes with special reference to the use of alternative protein sources able to replace soy bean, whose production accounts for about 60% GMO. The aim of the trial was to evaluate the possibility to replace soy bean with field bean for the heavy lamb diet and to study the effect of the processing treatment (extrusion) on the productive performances, the energy and protein metabolism parameters and on the quanti-qualitative characteristics of the carcass and the meat.Twenty-four male Gentile di Puglia lambs were divided, when 42 days old, into three homogeneous groups according to live weight (12,0 ± 0,5 kg) and assigned to the following feeding treatments: a) soy bean (control); b) raw field bean; c) extruded field bean. Food consumptions and live weights were recorded weekly in order to calculate the daily weight gain and the feed conversion index; blood samples were collected every 21 days and plasma concentration of glucose, triglycerides, cholesterol (energy metabolism), and BUN, total proteins, protein electrophoresis (protein metabolism) were measured. At 90 days of age, after 12 hours of fasting, lambs were slaughtered and the dressing percentage was calculated. After refrigeration at 4 °C for 24 hours, the carcasses were sectioned into cuts, and the pelvic limb and lumbar region were dissected into tissue components (lean, fat and bone) (ASPA, 1991). The pH values were measured at slaughtering and 24 h later on the Longissimus dorsi (Ld) and Semimembranosus (Sm) muscles. Meat colour features (L, a, b) were assessed by using a spectrophotometer (Hunter Lab, D65/10° illuminant). Data were analyzed by ANOVA using the GLM procedure of SAS and means were compared using the Student’s t test.The use of raw field bean showed better daily weight gain (250 g) when compared to c) group (220 g) and, especially, a) group (200 g, P<0.05). The blood indexes characterizing the energetic and protein metabolism were affected by lambs’ age but not by their feeding treatment. The pH of both the muscles, Ld and Sm, were not influenced by the feeding treatment at the slaughtering time, while 24 hours later the pH value of the Ld was significantly higher in the control group (6,10 ± 0,18) when compared to c) group (5.71 ± 0.02; P<0.01) and b) group (5.78±0,05; P<0.05). No statistical differences with regards to the incidence of the different cuts of the half carcass were detected among treatments. As for the tissue components of the pelvic limb cut, the percentage of lean in the control group (62.44±1.39) was lightly lower compared to the field bean groups, either extruded (63,28±2,15) or raw (64.44±0.67 %). The percentage of fat was lower for the extruded field bean treatment (9.03±0.78) with respect to that recorded with the use of soy bean (11.23 ± 0.60; P<0.05) or of raw field bean (12.83±0.78; P<0.01). With concern to the colorimetric characteristics of the Ld muscle, the index of redness was greater in the group fed with raw field bean when compared to control (10.39±0,42 vs 9.33±0.29; P<0.05). On the other hand, the brightness (37.90±1.44) and the yellowness (7.81±0.47) of the Sm muscle were significantly lower (P<0.05) in b) group when compared to a) and c) groups.It is concluded that field bean may represent a valid alternative to soy bean as a protein feed for growing lambs in so-called “organic” animal production systems where transgenic soy is banned.

Racial/ethnic disparities in basal muscle protein metabolism

Variability in body composition and muscle mass may be partially explained by race/ethnicity. The purpose of the current, ongoing study was to determine if race/ethnicity influences basal muscle protein metabolism. Using stable isotope methodologies, we measured muscle protein and amino acid metabolism in a multiethnic cohort of 49 healthy adult men (28±1 yrs) after an overnight fast. Preliminary results indicate that arterial and venous phenylalanine concentrations were significantly higher in Asians (ASI: 69±4 μmol/L) than Caucasians (C: 59±2, P<0.05), and muscle free phenylalanine concentrations were significantly higher in African Americans (AA: 126±15) than C: (95±6) and Hispanic (H: 85±5) (P<0.05). No differences in muscle protein synthesis were found between groups. Muscle breakdown (Ra, nmol/min/100 ml leg) was significantly higher (ASI 69±4, C: 57±5, P<0.05) and net balance (NB, nmol/min/100 ml leg) was significantly lower in ASI than C (ASI: −33±5, C: −16±2, P<0.05). NB significantly correlated with body weight and height (P<0.01) suggesting that body size may influence muscle protein turnover. In conclusion, key parameters of muscle protein and amino acid metabolism are influenced by ethnicity; however, these differences may simply reflect differences in body size. Support: NIH R01 AG18311, P30 AG17231

The effect of tomato consumption on selected protein and lipid metabolism parameters as well as on the oxidative and functional status of rat livers

1. Effects of Different Levels of Tomato Powder with and without Addition of Enzymes on Performance, Blood Parameters and Antioxidant Status of Japanese Quails bandforouzi Saharkhiz, Mansour Rezaei, Mohammad KazemiFard Research on Animal Production CrossRef

Aspects of Protein and Amino Acid Metabolism in a Model of Severe Glutamine Deficiency in Sepsis

Background/Aims: Growth hormone (GH) could have the potential to improve protein metabolism in sepsis but glutamine deficiency has been reported after GH treatment. The aim was to investigate the effects of glutamine deficiency in sepsis with and without GH treatment on protein and amino acid metabolism. Methods: Cecal ligation and puncture (CLP) was used as a model of sepsis. Serious glutamine deficiency was induced by administration of glutamine synthetase inhibitor, methionine sulfoximine (MSO). Young Wistar rats were divided into 5 groups: control; CLP; CLP+MSO; CLP+GH, and CLP+MSO+GH. Parameters of protein metabolism were measured on incubated soleus and extensor digitorum longus muscles: [1-¹⁴C]leucine was used to estimate protein synthesis and leucine oxidation, tyrosine release was used to evaluate protein breakdown. Amino acid concentrations in plasma, skeletal muscle and incubation media were measured by HPLC. Results/Conclusions: A reduced muscle glutamine concentration after MSO treatment is not associated with changes in the rates of protein synthesis or breakdown. MSO treatment decreased glutamine release from skeletal muscle and plasma glutamine concentration. Severe glutamine deficiency in GH-treated septic rats resulted in increased release of branched-chain amino acids from skeletal muscle.

Evaluation of the digestibility of Lathyrus sativus in growing pigs

The EU ban on meals of animal origin and the rejection by some States, including Italy, of genetically modified organisms (e.g. soybean), have resulted in the need for novel protein sources. The present study was undertaken to evaluate the digestibility of rations where soybean was partially replaced with Lathyrus sativus L. Twelve hybrid growing pigs were fed three diets formulated to be isoenergetic and isoproteic according to a Latin square design, each for 22 days. In the two experimental diets soybean was replaced by 10% or 20% L. sativus. Subjects were about 78 kg live weight at baseline. After 10 days of adaptation to each diet, faeces samples were collected from the rectum at the same time of day for 3 days. At the end of the administration of each diet, animals were weighed and blood was collected to determine some protein metabolism parameters. Feed and faeces were analysed for nutrients and AIA in order to calculate the coefficients of digestible utilisation of nutrients. Results were analysed by ANOVA using JMP (SAS system). The growth performance data (ADG and FCR) did not demonstrate differences attributable to the substitution of soybean with L. sativus. The coefficients of digestible utilisation indicate that soybean can be replaced with this legume seed. Low plasma urea in animals receiving 20% L. sativus confirmed the good metabolic efficiency of protein.

Effects of Clomazone Herbicide on hematological and some parameters of protein and carbohydrate metabolism of silver catfish Rhamdia quelen

The effects of clomazone (0.5 and 1.0 mg/L) according to nominal concentrations used in paddy rice fields (0.4–0.7 mg/L) on protein and carbohydrate metabolism and haematological parameters were evaluated in silver catfish ( Rhamdia quelen) after 12, 24, 48, 96 and 192 h of exposure with a recovery period of 96 and 192 h. Liver glycogen increased significantly ( P < 0.05 ) in all periods and concentrations tested. The maximum glycogen increase reaches 250% after 12 h of exposure. Muscle glycogen reduced significantly after 24, 48, 96 and 192 h for both clomazone concentrations ( P < 0.05 ). Significantly elevated plasma glucose values ( P < 0.05 ) and variation in glucose in the liver and muscle of exposed fish were observed. Muscle lactate levels increased after 12, 24 and 48 h of clomazone exposure (22–67%), but reduced in the liver ( P < 0.05 ). Protein levels were enhanced in the liver and white muscle, except at 96 and 192 h of exposure, whereas it increased in the plasma in the period from 48 to 96 h ( P < 0.05 ). Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activities were significantly elevated in the plasma ( P < 0.05 ). In the liver, ALT increased after 24 h, while AST activity was enhanced only after 12 h of exposure. Hematocrit contents were reduced after 96 and 192 h of exposure. Most of the metabolic disorders observed did not persist after the recovery period, except for the liver AST and ALT activity. Clomazone concentrations used in this study appear safe to fish, Rhamdia quelen, because overall parameters can be recovered after 96 and 192 h in clean water. ALT and AST activity may be an early biomarker of clomazone toxicity.

Arginine and Mixed Amino Acids Increase Protein Accretion in the Growth-Restricted and Normal Ovine Fetus by Different Mechanisms

Protein metabolism may be perturbed in intrauterine growth restriction (IUGR). Arginine is indispensable for growth and nitrogen balance in young mammals. Fetuses with IUGR therefore may benefit from arginine supplementation. The purpose of this study was to determine 1) the effects of IUGR on protein metabolism in the ovine fetus and 2) the effects of arginine or mixed amino acid (AA) infusion on protein metabolism in these fetuses. Pregnant ewes and their fetuses were catheterized at 110 d gestation and randomly assigned to control or IUGR groups. IUGR was induced by repetitive placental embolization. Parameters of fetal protein metabolism were determined from [ring-(2)H(5)]phenylalanine kinetics at baseline and in response to a 4-h infusion of either arginine or an isonitrogenous AA mixture. There were no differences in protein metabolism between control and IUGR groups either at baseline or in response to arginine or AA treatment. Both arginine and AA infusion increased fetal protein accretion in both groups. Arginine did this by decreasing protein turnover, synthesis, and breakdown. AAs increased protein turnover and synthesis while decreasing protein breakdown. AA infusion resulted in a significantly higher increase in protein accretion than arginine infusion. Thus, in the ovine fetus, placental embolization has no clear effect on protein metabolism. Arginine and AAs both stimulate protein accretion but do so in distinctly different ways. Mixed AA infusion has a greater effect on protein accretion than arginine alone and therefore may be a better strategy for stimulating fetal growth.

Lactation response of cows to different levels of ruminally inert conjugated linoleic acids under commercial conditions

Dietary conjugated linoleic acid (CLA) supplements have been shown to reduce milk fat synthesis in dairy cows. A rumen-inert source of CLA is required for commercial feed applications. The conversion of dietary lipids to a calcium salt is considered as a method to counter the extensive hydrogenation of dietary lipids that occurs in the rumen. Our objective was to determine whether feeding calcium salts of CLA under commercial conditions would affect milk production, milk composition and blood metabolic profile. A total of 240 dairy cows from eight farms were blocked according to the calving date, and randomly assigned to four treatments providing CLA at 0, 8, 16 and 32 g d-1. Milk production was recorded and milk was sampled on day 0, 7, 14, 28 and 42 of the feeding period. Blood samples were taken on day 42 from early-lactating cows (&lt; 157 d in milk) to determine the metabolic profile. Milk fat yield was decreased 11, 20 and 28%, and milk fat concentration was reduced 13, 22 and 28% (linear; P &lt; 0.001) when cows received 8, 16 and 32 g d-1 of CLA, respectively. Milk yield, milk protein and blood metabolic parameters were not affected by experimental treatments. Calcium salts of CLA can be used as an effective tool to manage milk fat content on commercial dairy farms. Key words: Conjugated linoleic acid, milk fat, ruminally inert fat

Membrane Biocompatibility Does Not Affect Whole Body Protein Metabolism during Dialysis

Background: Protein-calorie malnutrition is present in 30–50% of dialysis patients. The lack of biocompatibility of the dialysis membrane, which results in low-grade inflammation, could be responsible for this malnutrition. We investigated whether protein-energy malnutrition could be partly due to incompatibility of the dialyzer during the dialysis session. Methods: Five patients were dialyzed during 2 periods of 3 weeks (cross-over) with either a single-use low-flux polysulfone or cellulose triacetate (biocompatible) or a single-use cuprophan (bio-incompatible) membrane. As a measure of whole body protein metabolism, a primed constant infusion of L-[1-¹³C]-valine was used during a 4-hour dialysis session. Results: Cuprophan was a more powerful activator of the complement system than other membranes. Protein metabolism parameters during both study protocols were not different and resulted in the same protein balance during polysulfone/cellulose triacetate (–15 ± 3) and cuprophan (–13 ± 2 µmol/kg/h) dialysis. Conclusion: In stable hemodialysis patients with no apparent complications, protein metabolism during dialysis is not affected by the compatibility of the dialysis membrane.

Protein metabolism in guanethidine-treated rats.

The aim of the present study was to evaluate the effect of short-term adrenergic blockade on the rate of whole-body protein turnover and leucine oxidation, and on protein synthesis in specific tissues in male rats. Adrenergic blockade was induced by guanethidine (100 mg/kg body weight subcutaneously). The control group was treated with saline. On the second day, the parameters of whole-body protein and leucine metabolism were evaluated using a primed constant intravenous infusion of L-[1-(14)C]leucine. Protein synthesis in tissues was determined on the basis of L-[1-(14)C]leucine incorporation. Guanethidine treatment caused a decrease in norepinephrine in skeletal muscle. Whole-body leucine oxidation and leucine oxidized fraction were higher in guanethidine-treated rats. There was an insignificant effect of guanethidine on whole-body proteolysis, protein synthesis and leucine clearance. However, protein balance was negative due to the larger difference between protein synthesis and proteolysis in guanethidine-treated animals compared to controls. In guanethidine-treated rats, protein synthesis was higher in the gastrocnemius muscle and in the kidneys and lower in liver and spleen. Changes in the small intestine and colon were insignificant. In addition, a marked decrease in concentration of several amino acids has been observed in the liver, the kidneys and the spleen. It is concluded that adrenergic blockade induced by guanethidine is associated with significant changes in protein metabolism, leucine oxidation and amino acid concentrations in several tissues. The most important consequences of treatment are considered to be a negative effect on protein balance, increased protein turnover in skeletal muscle and kidneys and decreased protein synthesis in the liver and spleen. These changes may also be induced by administration of other sympathetic blocking agents, e.g. in treatment of hypertension.

Orlistat for obesity: benefits beyond weight loss

Orlistat lowers lipids and improves insulin sensitivity, but its effect on other metabolic syndrome related parameters is not known. To assess its influence on adiponectin, high sensitive C-reactive protein (hs-CRP) and other metabolic syndrome related parameters, this study enrolled 106 participants in a weight-reduction program and categorized them into a group of 51 who had been treated with orlistat 360 mg/day for one year and a group of 55 age and sex and body mass index (BMI) matched controls. The orlistat group had greater changes in BMI, % body fat (% BF), waist circumference, and insulin resistance, hs-CRP, leptin and adiponectin levels after one year on the program than the controls. After adjusting for % BF and waist circumference, change of serum leptin and adiponectin levels remained significantly different. It was found that orlistat could effectively manage obesity related co-morbidities, especially insulin resistance and atherosclerosis risk. It decreases leptin and increases adiponectin independent of % BF and waist circumference. Therefore, orlistat appears to have anti-diabetic and anti-atherogenic properties and may help prevent metabolic syndrome in the overweight people.

Response of Cyprinus carpio (Linn) to sublethal concentration of cypermethrin: alterations in protein metabolic profiles

Freshwater fish, Cyprinus carpio were exposed to sublethal concentration (1.2 μg l −1) of cypermethrin for 6, 12, 24 and 48 h to analyze various parameters of protein metabolism in functionally different tissues. Total, structural and soluble proteins showed decrement; where as free amino acids and the activities of protease, aspartate aminotransferase and alanine aminotransferase significantly increased in cypermethrin exposed fish. Interestingly, ammonia content decreased but urea and glutamine increased at all periods of exposure. It was also observed that alterations steadily increased with the period of exposure and exhibited tissue specificity. Thus variation in the protein metabolism of the fish exposed to cypermethrin indicates its toxic effect on the cellular metabolism thereby leading to impaired protein synthetic machinery.

Post-hatching dynamics of plasma biochemistry in free-living European starlings ( Sturnus vulgaris)

This is the first study of plasma biochemical parameters in free-living altricial birds during an entire developmental period in a nest, represented by European starling ( Sturnus vulgaris). Dynamics of postnatal changes from hatching until close to fledging (days 1 to 15) were registered. Parameters of protein metabolism represented by total proteins, albumin and globulin concentrations increased continuously during the observed developmental period. There were two peaks in uric acid concentration on days 5 and 11. To the contrary, the creatinine content did not change throughout the observed period and increased only on day 15. Creatine kinase activity gradually increased until day 11 and then fell before fledging. Parameters of lipid metabolism (concentration of total lipids, triacylglycerols and nonesterified fatty acids) in plasma increased gradually reaching a plateau between days 8 and 11 and then declined on day 15. The cholesterol concentration pattern was similar to maximum value on day 11, then consecutively decreased. Concentration of glucose increased until day 8 and remained unchanged until fledging. Whereas calcium reached the highest concentration during days 8 and 11, phosphorus peaked earlier on day 5. The activity of alkaline phosphatase was similar to the pattern found in calcium concentration. Presented data showed an increase in both protein and lipid metabolism during the phase of rapid growth. A remarkable decrease in parameters of lipid metabolism before fledging may reflect increased physical activity and changes in nutrition.

Post-hatching dynamics of plasma biochemistry in free-living European starlings (Sturnus vulgaris)

This is the first study of plasma biochemical parameters in free-living altricial birds during an entire developmental period in a nest, represented by European starling (Sturnus vulgaris). Dynamics of postnatal changes from hatching until close to fledging (days 1 to 15) were registered. Parameters of protein metabolism represented by total proteins, albumin and globulin concentrations increased continuously during the observed developmental period. There were two peaks in uric acid concentration on days 5 and 11. To the contrary, the creatinine content did not change throughout the observed period and increased only on day 15. Creatine kinase activity gradually increased until day 11 and then fell before fledging. Parameters of lipid metabolism (concentration of total lipids, triacylglycerols and nonesterified fatty acids) in plasma increased gradually reaching a plateau between days 8 and 11 and then declined on day 15. The cholesterol concentration pattern was similar to maximum value on day 11, then consecutively decreased. Concentration of glucose increased until day 8 and remained unchanged until fledging. Whereas calcium reached the highest concentration during days 8 and 11, phosphorus peaked earlier on day 5. The activity of alkaline phosphatase was similar to the pattern found in calcium concentration. Presented data showed an increase in both protein and lipid metabolism during the phase of rapid growth. A remarkable decrease in parameters of lipid metabolism before fledging may reflect increased physical activity and changes in nutrition.

Acute effects of acidosis on protein and amino acid metabolism in perfused rat liver.

Acidosis is frequently associated with protein wasting and derangements in amino acid metabolism. As its effect on protein metabolism is significantly modulated by other abnormal metabolic conditions caused by specific illnesses, it is difficult to separate out the effects on protein metabolism solely due to acidosis. The aim of the present study was to evaluate, using a model of isolated perfused rat liver, the direct response of hepatic tissue to acidosis. We have compared hepatic response to perfusion with a solution of pH 7.2 and 7.4 (controls). Parameters of protein and amino acid metabolism were measured using both recirculation and single-pass technique with 4,5-[3H]leucine, [1-14C]leucine and [1-14C]ketoisocaproate (ketoleucine) as tracers and on the basis of difference of amino acid levels in perfusion solution at the beginning and end of perfusion. In liver perfused with a solution of pH 7.2, we observed higher rates of proteolysis, protein synthesis, amino acid utilization and urea production. Furthermore, the liver perfused with a solution of pH 7.2 released a higher amount of proteins to perfusate than the liver perfused with a solution of pH 7.4. Enhanced decarboxylation of ketoisocaproate in liver perfused by a solution of a lower pH indicates increased catabolism of branched-chain amino acids (leucine, valine and isoleucine), decreased reamination of branched-chain keto acids to corresponding essential amino acids and increased ketogenesis from leucine.

Proteomic sensitivity to dietary manipulations in rainbow trout

Changes in dietary protein sources due to substitution of fish meal by other protein sources can have metabolic consequences in farmed fish. A proteomics approach was used to study the protein profiles of livers of rainbow trout that have been fed two diets containing different proportions of plant ingredients. Both diets control (C) and soy (S) contained fish meal and plant ingredients and synthetic amino acids, but diet S had a greater proportion of soybean meal. A feeding trial was performed for 12 weeks at the end of which, growth and protein metabolism parameters were measured. Protein growth rates were not different in fish fed different diets; however, protein consumption and protein synthesis rates were higher in the fish fed the diet S. Fish fed diet S had lower efficiency of retention of synthesised protein. Ammonia excretion was increased as well as the activities of hepatic glutamate dehydrogenase and aspartate amino transferase (ASAT). No differences were found in free amino acid pools in either liver or muscle between diets. Protein extraction followed by high-resolution two-dimensional electrophoresis, coupled with gel image analysis, allowed identification and expression of hundreds of protein. Individual proteins of interest were then subjected to further analysis leading to protein identification by trypsin digest fingerprinting. During this study, ∼800 liver proteins were analysed for expression pattern, of which 33 were found to be differentially expressed between diets C and S. Seventeen proteins were positively identified after database searching. Proteins were identified from diverse metabolic pathways, demonstrating the complex nature of gene expression responses to dietary manipulation revealed by proteomic characterisation.

Acute effects of decreased glutamine supply on protein and amino acid metabolism in hepatic tissue: a study using isolated perfused rat liver

Glutamine deficiency, a common finding in severe illness, has a negative influence on immune status, protein metabolism, and disease outcome. In several studies, a close relationship between glutamine, branched-chain amino acid (BCAA), and protein metabolism was demonstrated. The aim of the present study was to investigate the effect of glutamine deficiency on amino acid and protein metabolism in hepatic tissue using a model of isolated perfused rat liver (IPRL). Parameters of protein metabolism and amino acid metabolism were measured using both recirculation and single pass technique with L-[1- 14C]leucine and [1- 14C]ketoisocaproate (KIC) as a tracer. Glutamine concentration in perfusion solution was 0.5 mmol/L in control and 0 mmol/L in the glutamine-deficient group. The net release of glutamine (about 11 μmol/g/h) and higher net uptake of most of the amino acids was observed in the glutamine-deficient group. There was an insignificant effect of lack of glutamine on hepatic protein synthesis, proteolysis, and the release of urea. However, significantly lower release of proteins by the liver perfused with glutamine-deficient solution was observed. The lack of glutamine in perfusion solution caused a significant decrease in leucine oxidation (6.66 ± 1.04 v 13.67 ± 2.38, μmol/g dry liver/h, P < .05) and an increase in KIC oxidation (163.7 ± 16.5 v 92.0 ± 12.9 μmL/g dry liver/h, P < .05). We conclude that decreased delivery of glutamine to hepatic tissue activates glutamine synthesis, decreases resynthesis of essential BCAA from branched-chain keto acids (BCKA), increases catabolism of BCKA, and has an insignificant effect on protein turnover in hepatic tissue.

Effect of decreased glutamine supply on protein and amino acid metabolism in hepatic tissue. A study using isolated perfused rat liver

Glutamine deficiency, a common finding in severe illness, has a negative influence on immune status, protein metabolism, and disease outcome. In several studies, a close relationship between glutamine, branched-chain amino acid (BCAA), and protein metabolism was demonstrated. The aim of the present study was to investigate the effect of glutamine deficiency on amino acid and protein metabolism in hepatic tissue using a model of isolated perfused rat liver (IPRL). Parameters of protein metabolism and amino acid metabolism were measured using both recirculation and single pass technique with L-[1C]leucine and [1-C]ketoisocaproate (KIC) as a tracer. Glutamine concentration in perfusion solution was 0.5 mmol/L in control and 0 mmol/L in the glutamine-deficient group. The net release of glutamine (about 11 mol/g/h) and higher net uptake of most of the amino acids was observed in the glutamine-deficient group. There was an insignificant effect of lack of glutamine on hepatic protein synthesis, proteolysis, and the release of urea. However, significantly lower release of proteins by the liver perfused with glutamine-deficient solution was observed. The lack of glutamine in perfusion solution caused a significant decrease in leucine oxidation (6.66 1.04 v 13.67 2.38, mol/g dry liver/h, P < .05) and an increase in KIC oxidation (163.7 16.5 v 92.0 12.9 mL/g dry liver/h, P < .05). We conclude that decreased delivery of glutamine to hepatic tissue activates glutamine synthesis, decreases resynthesis of essential BCAA from branched-chain keto acids (BCKA), increases catabolism of BCKA, and has an insignificant effect on protein turnover in hepatic tissue. © 2003 Elsevier Inc. All rights reserved.