Effects of an amino acid dialysate on leucine metabolism in continuous ambulatory peritoneal dialysis patients

The Effect of Nutrition and Exercise on Body Composition, Exercise Capacity, and Physical Functioning in Advanced CKD Patients

Patients with stages 4 and 5 chronic kidney disease (CKD), and particularly chronic dialysis patients, commonly are found to have substantially reduced daily physical activity in comparison to age- and sex-matched normal adults. This reduction in physical activity is associated with a major decrease in physical exercise capacity and physical performance. The CKD patients are often physically deconditioned, and protein energy wasting (PEW) and frailty are commonly present. These disorders are of major concern because physical dysfunction, muscle atrophy, and reduced muscle strength are associated with poor quality of life and increased morbidity and mortality in CKD and chronic dialysis patients. Many randomized controlled clinical trials indicate that when CKD and chronic dialysis are provided nutritional supplements or undergo exercise training their skeletal muscle mass and exercise capacity often increase. It is not known whether the rise in skeletal muscle mass and exercise capacity associated with nutritional support or exercise training will reduce morbidity or mortality rates. A limitation of these clinical trials is that the sample sizes of the different treatment groups were small. The aim of this review is to discuss the effects of nutrition and exercise on body composition, exercise capacity, and physical functioning in advanced CKD patients.

Chronic Kidney Disease and Nutrition Support

Individuals with chronic kidney disease (CKD), particularly those undergoing maintenance dialysis, are prone to protein-energy wasting (PEW), the latter of which can be ameliorated with different methods of nutrition support. Dietary counseling guided by dietitians is the key for preventing and managing PEW in CKD. If dietary counseling per se fails to meet the recommended energy and protein requirements, the addition of oral nutrition supplements (ONSs) would be necessary. When these initial measures cannot attain the recommended energy and protein requirements, nutrition support, including enteral tube feeding or parenteral nutrition (PN), should be considered as a viable option to improve nutrition status. Partial PN, comprising intraperitoneal PN (IPPN) and intradialytic PN (IDPN) therapies, may be attempted as supplemental nutrition support in patients with PEW requiring peritoneal dialysis and hemodialysis, respectively. Despite the debatable effectiveness of IPPN for patients undergoing peritoneal dialysis, it remains a feasible means in these patients. The indications for IPPN in patients undergoing peritoneal dialysis include inadequate dietary intake of energy and protein, and barriers of oral intake and other forms of enteral supplementation such as issues with suitability, tolerance, and compliance. Nonetheless, in the case of spontaneous dietary consumption of energy and protein meeting the difference between the IDPN provision and the nutrition targets, the use of IDPN is rational. In patients with PEW and malfunctioning gastrointestinal tract, as well as those whose enteral intake (with or without partial PN) is below the recommended nutrient requirements, total PN becomes a relevant nutrition intervention.

The osmo-metabolic approach: a novel and tantalizing glucose-sparing strategy in peritoneal dialysis

Peritoneal dialysis (PD) is a viable but under-prescribed treatment for uremic patients. Concerns about its use include the bio-incompatibility of PD fluids, due to their potential for altering the functional and anatomical integrity of the peritoneal membrane. Many of these effects are thought to be due to the high glucose content of these solutions, with attendant issues of products generated during heat treatment of glucose-containing solutions. Moreover, excessive intraperitoneal absorption of glucose from the dialysate has many potential systemic metabolic effects. This article reviews the efforts to develop alternative PD solutions that obviate some of these side effects, through the replacement of part of their glucose content with other osmolytes which are at least as efficient in removing fluids as glucose, but less impactful on patient metabolism. In particular, we will summarize clinical studies on the use of alternative osmotic ingredients that are commercially available (icodextrin and amino acids) and preclinical studies on alternative solutions under development (taurine, polyglycerol, carnitine and xylitol). In addition to the expected benefit of a glucose-sparing approach, we describe an ‘osmo-metabolic’ approach in formulating novel PD solutions, in which there is the possibility of exploiting the pharmaco-metabolic properties of some of the osmolytes to attenuate the systemic side effects due to glucose. This approach has the potential to ameliorate pre-existing co-morbidities, including insulin resistance and type-2 diabetes, which have a high prevalence in the dialysis population, including in PD patients.

Biocompatibility of New Peritoneal Dialysis Solutions: What Can We Hope to Achieve?

Despite the bioincompatibility of the “old”, standard, high glucose, lactate-buffered peritoneal dialysis (PD) solutions, PD is itself a highly successful dialysis modality with patient survival equivalent to that of hemodialysis (HD) during the initial 3 – 5 years of dialysis therapy. Nevertheless, PD technique survival is often limited by infectious complications and alterations in the structure and function of the peritoneal membrane. These local changes also have a negative impact on patient survival owing to systemic effects such as those often seen in patients with high peritoneal transport rate and loss of ultrafiltration (UF) capacity.

Patient mortality remains unacceptably high in both HD and PD patients, with most premature deaths being associated with signs of malnutrition, inflammation, and atherosclerotic cardiovascular disease (MIA syndrome). These systemic signs are likely to be influenced by PD solutions both directly and indirectly (via changes in the peritoneal membrane). New, biocompatible PD solutions may have favorable local effects (viability and function of the peritoneal membrane) and systemic effects (for example, on MIA syndrome). Amino acid–based solution [Nutrineal (N): Baxter Healthcare Corporation, Deerfield, IL, U.S.A.] may improve nutritional status as well as peritoneal membrane viability. Bicarbonate/lactate–buffered solution [Physioneal (P): Baxter Healthcare Corporation] may ameliorate local and systemic effects of low pH, high lactate, and high glucose degradation products. Icodextrin-based solution [Extraneal (E): Baxter Healthcare SA, Castlebar, Ireland] may improve hypertension and cardiovascular problems associated with fluid overload and may extend time on therapy in patients with loss of UF capacity.

The positive effects of each of these new, biocompatible solutions have been demonstrated in several studies. It is likely that the combined use of N, P, and E solutions will produce favorable synergies in regard to both local effects (peritoneal viability) and systemic effects (less malnutrition, inflammation, and fluid overload). Solution combination is an exciting area for clinical study in the coming years. Furthermore, dialysis fluid additives such as hyaluronan, which protects and improves the function of the peritoneal membrane, may further improve PD solutions. The new, biocompatible PD solutions represent an entirely new era in the evolution of the PD therapy; they are likely to have markedly positive effects on both PD technique and PD patient survival in coming years.

Nutrition in Older Adults on Peritoneal Dialysis

Nutrition in older adults on peritoneal dialysis is an important aspect of a patient's clinical management as well as being influenced by their overall well-being, both mental and physical. This is especially pertinent as individuals age, since the potential impact of life changes and physical changes contribute to the development of protein-energy wasting and potentially exacerbating sarcopenia and wasting. This article provides an outline of the nutritional issues to consider in older adults on peritoneal dialysis (PD).

[The specific nutritionnal care in peritoneal dialysis]

Protein energy wasting is a major complication in peritoneal dialysis. It is leading to a poor quality of life and increasing mortality. Diagnosis must be early, according to criteria defined by the International society of renal nutrition and metabolism. It is necessary to appropriate the diagnostic tools with dialysis method. The nutritional care is difficult in peritoneal dialysis. Indeed, studies are limited and practical nutrition is complex. In this point of view, we propose to treat guidelines for protein energy wasting, in peritoneal dialysis patients.

Nutritional issues in peritoneal dialysis patients: how do they differ from that of patients undergoing hemodialysis?

It is important to understand the unique aspects vis-à-vis protein-energy wasting for patients undergoing PD. As a result of obligatory protein losses with the therapy, the serum albumin levels of patients undergoing PD are lower, as is the threshold serum albumin at which the risk for death is increased. Consequently, it is prudent to consider a lower threshold for serum albumin for the diagnosis of protein-energy wasting for patients undergoing PD. Likewise, it is important to consider the energy intake from obligatory nutrient absorption in the form of carbohydrates when estimating total energy intake (diet and dialysate) when evaluating patients for protein-energy wasting. The continuous nature of PD also has important therapeutic implications for protein-energy wasting. Such patients are more likely to have a complete correction of metabolic acidosis, and glucose absorption from the peritoneal dialysate has a protein-sparing effect, allowing some patients to maintain neutral nitrogen balances in the face of suboptimal protein intake. In contrast, clinical trials of amino-acid-based PD solutions have not met expectations and cannot be recommended for routine use for treatment of protein-energy wasting. In conclusion, it is important to consider these unique nutritional considerations when providing care to patients undergoing PD.

Association between direct measures of body composition and prognostic factors in chronic heart failure

OBJECTIVE

To explore the covariate-adjusted associations between body composition (percent body fat and lean body mass) and prognostic factors for mortality in patients with chronic heart failure (CHF) (nutritional status, N-terminal pro-B-type natriuretic peptide [NT-proBNP], quality of life, exercise capacity, and C-reactive protein).

PATIENTS AND METHODS

Between June 2008 and July 2009, we directly measured body composition using dual energy x-ray absorptiometry in 140 patients with systolic and/or diastolic heart failure. We compared body composition and CHF prognostic factors across body fat reference ranges and body mass index (BMI) categories. Multiple linear regression models were created to examine the independent associations between body composition and CHF prognostic factors; we contrasted these with models that used BMI.

RESULTS

Use of BMI misclassified body fat status in 51 patients (41%). Body mass index was correlated with both lean body mass (r=0.72) and percent body fat (r=0.67). Lean body mass significantly increased with increasing BMI but not with percent body fat. Body mass index was significantly associated with lower NT-proBNP and lower exercise capacity. In contrast, higher percent body fat was associated with a higher serum prealbumin level, lower exercise capacity, and increased C-reactive protein level; lean body mass was inversely associated with NT-proBNP and positively associated with hand-grip strength.

CONCLUSION

When BMI is divided into fat and lean mass components, a higher lean body mass and/or lower fat mass is independently associated with factors that are prognostically advantageous in CHF. Body mass index may not be a good indicator of adiposity and may in fact be a better surrogate for lean body mass in this population.

Anabolic and catabolic mechanisms in end-stage renal disease

Muscle wasting is a prominent feature of end-stage renal disease and is associated with muscle weakness and poor physical functioning. Potential reasons for muscle wasting include advancing age, sedentary behavior, inflammation, poor nutritional intake, androgen deficiency, oxidative stress, metabolic acidosis, and insulin resistance. Each of these conditions can be associated with decreased protein synthesis, increased protein degradation, or both. The primary muscle protein synthesis pathway is the insulin insulin-like growth factor-1/phosphatidyl inositol-3 kinase/Akt pathway, which results in the phosphorylation of the mammalian target of rapamycin and subsequent increased protein synthesis. The major protein degradation pathway is the ubiquitin-proteasome system. This review discusses the ways in which end-stage renal disease tips the balance of protein turnover towards catabolism and the mechanisms by which various interventions may work to mitigate wasting or even cause anabolism.

Amino Acid-Based Peritoneal Dialysis Solutions for Malnutrition: New Perspectives

Protein and energy malnutrition is frequently found in patients on maintenance dialysis and is associated with an increased risk of death. Among a variety of factors involved in the development of protein and energy malnutrition, such as acidosis, insulin resistance, inflammation, and dialysate protein losses, insufficient intake of proteins and energy as a result of anorexia plays a prominent role.

Amino acid (AA)-based peritoneal dialysis (PD) solutions can induce an anabolic response in malnourished patients on continuous ambulatory PD if enough calories are ingested simultaneously. Poor appetite, however, may impede the intake of sufficient calories. Peritoneal dialysis solutions containing a mixture of AAs and glucose in a proper ratio can serve as a source of proteins and calories. Such a dialysis solution can be used in fasting patients on nocturnal automated PD as part of a regular dialysis schedule. Using a sophisticated technique involving stable isotopes, this dialysis mixture has been found to induce acute anabolic changes in whole body protein metabolism. Such a metabolic response is similar to that induced by food. Intraperitoneal AAs, in common with ingested proteins, can induce generation of hydrogen ions and urea through oxidation of specific AAs. Supplying AAs together with calories could bring about utilization of AAs for the synthesis of proteins rather than the oxidation of AAs, thereby limiting production of acid and urea. Using dialysis solutions with a buffer concentration of 40 mmol/L further contributes to maintaining acid–base homeostasis.

We advocate consideration of usage of AA/glucose dialysate when PD patients cannot comply with dietary requirements. To evaluate the long-term effects of this approach on morbidity and mortality, clinical trials with large groups of patients are needed.

Dialysate as food as an option for automated peritoneal dialysis

Protein-energy malnutrition is frequently found in dialysis patients. Many factors play a role in its development including deficient nutrient intake as a result of anorexia. Peritoneal dialysis (PD) solutions containing a mixture of amino acids and glucose in an appropriate ratio could serve as a source of food. The authors of this article found that such a dialysis solution when administered to fasting patients who were on nightly automated peritoneal dialysis (APD), as part of a regular dialysis schedule, induced an acute anabolic effect. Also in PD patients in the fed state, dialysis solutions containing both amino acids and glucose were found to improve protein metabolism. It appears that the body responds similar to intraperitoneal and oral amino acid:dialysate as food. Like dietary proteins, intraperitoneal amino acids can bring about generation of hydrogen ions and urea as a result of oxidation. No rise of serum urea levels was found and serum bicarbonate remained within the normal range when a total buffer concentration of 40 mmol/L in the mixture was used. The use of this approach may be an option for PD patients who cannot fulfil dietary recommendations.

Update on peritoneal dialysis solutions

Since the widespread introduction of peritoneal dialysis (PD) into the standard care of patients with chronic kidney disease there has been a shift from the initial focus on technique survival to refinement of the therapy to enhance biocompatibility and improve both the local peritoneal and systemic consequences of PD. One of the most significant contributions to these advances has been the development of novel PD solutions. The use of new manufacturing techniques, buffer presentation, and new osmotic alternatives to glucose have allowed potentially improved peritoneal survival (in terms of structure and function) and improved subjective patient experience. Additional benefits have also included, enhanced management of salt and water removal, supported nutritional status and improvement in the systemic metabolic derangements associated with conventional PD treatment, based on glucose-containing lactate-buffered solutions. The selection of suitable targets for modulation of therapy continues to be hampered by our continued relative ignorance of the local and particularly systemic effects of PD compounded by the dearth of quality, outcome-based studies. The aim of this review is to summarize the characteristics of the next generation of PD fluids currently available, and then to evaluate their possible place in treatment by considering the difference in their effects in a series of structural and functional areas potentially relevant to improving patient outcomes.

Peritoneal dialysis with solutions containing amino acids plus glucose promotes protein synthesis during oral feeding

Inadequate food intake plays an important role in the development of malnutrition. Recently, an increased rate of protein anabolism was shown in fasting state in patients who were on automated peritoneal dialysis with combined amino acids (AA) and glucose (G) dialysate serving as a source of both proteins and calories. This study investigated the effects of such a dialysis procedure in the daytime in the fed state in patients who were on continuous ambulatory peritoneal dialysis (CAPD). A crossover study was performed in 12 CAPD patients to compare, at 7-d intervals, a mixture of AA (Nutrineal 1.1%) plus G (Physioneal l.36 to 3.86%) versus G only as control dialysate. Whole-body protein turnover was studied by primed constant intravenous infusion of (13)C-leucine during the 9-h dialysis. For meeting steady-state conditions during whole-body protein turnover, frequent exchanges with a mixture of AA plus G were done using an automated cycler. Fed-state conditions were created by identical liquid hourly meals. Using AA plus G dialysate, as compared with the control, rates of protein synthesis increased significantly (2.02 +/- 0.08 versus 1.94 +/- 0.07 mumol leucine/kg per min [mean +/- SEM]; P = 0.039). Rates of protein breakdown and net protein balance did not differ significantly between AA plus G and G. In conclusion, dialysate that contains AA plus G also improves protein synthesis in fed CAPD patients. The use of such a mixture may contribute to long-term improvement of the nutritional status in malnourished CAPD patients with deficient food intake.

Amino Acid and protein kinetics in renal failure: an integrated approach

Even apparently healthy patients on dialysis have significant loss of lean body mass. Patients with chronic renal failure without coexisting metabolic acidosis or inflammation have decreased protein turnover, with balanced reduction in protein synthesis and breakdown. However, regional and whole-body protein kinetic studies indicate that hemodialysis (HD) induces net increase in protein breakdown. Whole-body protein turnover studies show that HD is associated with decreased protein synthesis, but proteolysis is not increased. Muscle protein kinetics studies, however, identify enhanced muscle protein breakdown with inadequate compensatory increases in synthesis as the cause of the catabolism. Transmembrane amino acid-transport kinetics studies show that the outward transport is increased more than the inward transport of amino acids during HD. Altered intracellular amino acid transport kinetics and protein turnover during HD could be caused by the loss of amino acids in the dialysate or cytokine activation. Cytokines may be released from peripheral blood mononuclear cells and skeletal muscle during HD. Preliminary evidence indicates that intradialytic increase in cytokines activates the ubiquitin-proteasome pathway. An intradialytic increase in albumin and fibrinogen synthesis is facilitated by interleukin-6 and the constant supply of amino acids derived from skeletal muscle catabolism. Protein anabolism can be induced in end-stage renal disease patients by repletion of amino acids, and perhaps treatment with recombinant human insulin-like growth factor.

Dialysate as Food: Combined Amino Acid and Glucose Dialysate Improves Protein Anabolism in Renal Failure Patients on Automated Peritoneal Dialysis

Protein-energy malnutrition as a result of anorexia frequently occurs in dialysis patients. In patients who are on peritoneal dialysis (PD), dialysate that contains amino acids (AA) improves protein anabolism when combined with a sufficient oral intake of calories. It was investigated whether protein anabolism can be obtained with a mixture of AA plus glucose (G) as a source of proteins and calories during nocturnal automated PD (APD). A random-order cross-over study was performed in eight APD patients to compare in two periods of 7 d each AA plus G dialysate obtained by cycler-assisted mixing of one bag of 2.5 L of AA (Nutrineal 1.1%, 27 g of AA) and four bags of 2.5 L of G (Physioneal 1.36 to 3.86%) versus G as control dialysate. Whole-body protein turnover was determined using a primed continuous infusion of L-[1-13C]leucine, and 24-h nitrogen balance studies were performed. During AA plus G dialysis, when compared with control, rates of protein synthesis were 1.20 +/- 0.4 and 1.10 +/- 0.2 micromol/kg per min leucine (mean +/- SD), respectively (NS), and protein breakdown rates were 1.60 +/- 0.5 and 1.72 +/- 0.3 micromol/kg per min (NS). Net protein balance (protein synthesis minus protein breakdown) increased on AA plus G in all patients (mean 0.21 +/- 0.12 micromol leucine/kg per min; P < 0.001). The 24-h nitrogen balance changed by 0.96 +/- 1.21 g/d, from -0.60 +/- 2.38 to 0.35 +/- 3.25 g/d (P = 0.061, NS), improving in six patients. In conclusion, APD with AA plus G dialysate improves protein kinetics. This dialysis procedure may improve the nutritional status in malnourished PD patients.

A 3-year, prospective, randomized, controlled study on amino acid dialysate in patients on CAPD

BACKGROUND

Malnutrition is prevalent in patients on continuous ambulatory peritoneal dialysis (CAPD) and confers a poor prognosis. Inadequate nutrient intake is an important contributing factor. Although short-term studies have shown mild to modest nutritional benefit with amino acid dialysate, its long-term effects and tolerability remain obscure.

METHODS

The authors have performed a 3-year, randomized, prospective, controlled study of amino acid dialysate in malnourished Chinese patients on CAPD. Sixty patients were assigned randomly to either replace 1 exchange daily with amino acid dialysate (Nutrineal; DAA group, n = 30) or to continue with dextrose dialysate (Dianeal; DD group, n = 30).

RESULTS

The 2 groups had similar mortality, hospitalization duration, serial C-reactive protein levels, and drop-out rates during the study. Biochemical nutritional parameters including albumin and cholesterol decreased in the DD group but remained stable or increased in the DAA group. The composite nutritional index did not differ between the 2 groups throughout the study period. Triglyceride decreased only in DAA-treated patients. Normalized protein equivalent of nitrogen appearance and dietary protein intake showed a sustained increase only in DAA patients. The nutritional benefit of DAA appeared more prominent in women, whose lean body mass and body mass index was maintained with DAA but not with DD. Mass transfer area coefficient for creatinine increased in DAA-treated patients, whereas that for urea as well as macromolecular restriction coefficients remained stable. Total Kt/V(urea) and daily ultrafiltration volume were similarly maintained in the 2 groups throughout the study.

CONCLUSION

Long-term administration of amino acid dialysate is well tolerated and presents a means to improve the nutritional status in high-risk patients. The current study, however, has not shown a significant effect of amino acid dialysate on patient survival.

Protein and energy nutrition among adult patients treated with chronic peritoneal dialysis

Protein-energy malnutrition (PEM) in adult patients treated with chronic peritoneal dialysis (CPD), which is highly prevalent and frequently severe in its manifestation, poses a significant therapeutic dilemma. The causes of PEM include inflammation, low nutrient intake, nutrient losses during dialysis, metabolic acidemia, coexisting illnesses, and possibly the endocrine disorders of uremia. Treatment strategies for PEM in CPD patients include the following: attempt to treat the potentially reversible causes of anorexia, increase nutrient intake (by nutritional counseling, oral food supplements, consideration of appetite stimulants and intraperitonial amino acid solutions), and the correction of metabolic acidosis. Coexisting illnesses engendering PEM should be treated. Experimental evidence suggests that such agents as anabolic steroids, human growth hormone, insulin-like growth factor-I, and L-carnitine may engender positive protein balance in these individuals. Finally, the use of anti-inflammatory agents to improve the nutritional status of malnourished CPD patients remains to be defined. There is a need to carry out clinical trials that examine whether an improvement in the nutritional status of CPD patients is associated with an improvement in their mortality, morbidity and/or quality of life.

Leucine suppresses acid-induced protein wasting in L6 rat muscle cells

BACKGROUND

Metabolic acidosis induces protein wasting in skeletal muscle cells, accompanied by decreased glycolysis and compensatory increased consumption of other metabolic fuels, implying that protein wasting arises from fuel starvation and might be rectified by fuel supplements. Design To test this hypothesis, total protein and protein degradation (release of 14C-phenylalanine) were measured in L6 skeletal muscle cells cultured in Eagle's Minimum Essential Medium at pH 7.1-7.5 for 3 days with metabolic inhibitors or metabolic fuel supplements.

RESULTS

Inducing metabolic fuel starvation with inhibitors (1 mmol L(-1) 2-deoxyglucose or 0.1 mmol L(-1) KCN [potassium cyanide]) failed to stimulate protein degradation or net protein wasting under nonacidaemic conditions (pH 7.5). Conversely metabolic fuel supplements (1 mmol L(-1) octanoate, pyruvate or alanine) failed to increase the protein content of the cultures at any pH tested, in spite of significant consumption of the fuels by the cells. Only leucine (1-3 mmol L(-1)) increased protein content and suppressed protein degradation in opposition to the catabolic effect of acidaemia (pH 7.1). Conclusion Leucine exerts a beneficial anabolic effect on cultured skeletal muscle cells in the face of metabolic acidaemia. The failure of other metabolic fuels to do this, and of the metabolic inhibitors to exert a catabolic effect, suggests that leucine acts as a specific modulator of protein turnover and not as a nonspecific source of carbon for oxidation as a fuel.

Acute effects of simultaneous intraperitoneal infusion of glucose and amino acids

BACKGROUND

The feasibility of simultaneously infusing glucose and amino acid (AA)-based peritoneal dialysis solutions was tested to determine whether peritoneal dialysis patients could achieve an adequate nonprotein calorie/nitrogen ratio while preventing a marked increase in blood urea nitrogen (BUN), which is usually seen if the AAs are administered without glucose.

METHODS

An automatic peritoneal dialysis cycler was used to infuse glucose and AA solutions (3:1) simultaneously during the night. Eight infusions of 1000 mL m2 of body surface area (BSA), with a 60 minute dwell time, were performed in 10 children on peritoneal dialysis. The dialytic effluent was analyzed at every exchange and totaled at eight hours to evaluate volume, glucose, and AA concentration. Blood samples for plasma, glucose, insulin, and free AA determination were drawn at the beginning of automated peritoneal dialysis (APD) session and at each instillation of peritoneal dialysate.

RESULTS

The mean glucose absorption was 33.7 +/- 10.0% and the AA absorption was 55.2 +/- 13.2% of the infused amount, and the ratio of nonprotein calorie (derived from glucose) to nitrogen (derived from AA) was 115.4:1. The insulin levels returned to normal only three hours after the beginning of APD. The free AA plasma levels were already increased two hours after dinner and remained high for the entire APD treatment because of the continuous absorption of AA from the peritoneum. The BUN levels did not increase despite the supply of AA.

CONCLUSIONS

This APD procedure may improve utilization of AA for protein synthesis, as suggested by the lack of increase of the BUN levels with this regimen.

Acute effects of peritoneal dialysis with dialysates containing dextrose or dextrose and amino acids on muscle protein turnover in patients with chronic renal failure

Whether changes in substrate and insulin levels that occur during peritoneal dialysis (PD) have effects on muscle protein dynamics was evaluated by studying muscle protein synthesis (PS), breakdown (PB), and net protein balance (NB) by the forearm perfusion method associated with the kinetics of 3H-phenylalanine in acute, crossover studies in which PD patients served as their own controls. Studies were performed (1) in the basal state and during PD with dialysates that contained dextrose alone in different concentrations (protocol 1: eight patients), (2) during PD with dialysates that contained dextrose alone or dextrose and amino acids (AA) (protocol 2: five patients), and (3) in time controls (five patients). PD with dextrose alone induced (1) a two- to threefold increase in insulin, as well as a 20 to 25% decrease in AA, mainly BCAA, levels; (2) an insulin-related decline (-18%) in forearm PB (P<0.002); (3) a 20% decrease in muscle PS (P<0.04), which was related to arterial BCAA and K+ (P<0.02 to 0.05); (4) a persistent negative NB; and (5) a decrease in the efficiency of muscle protein turnover, expressed as the ratio NB/PB. PD with dextrose+AA versus PD with dextrose induced (1) similarly high insulin levels but with a significant increase in total arterial AA (+30 to 110%), mainly valine; (2) a reduced release of AA from muscle (P<0.05); and (3) a decrease in the negative NB observed during PD with dextrose, owing to an increase (approximately 20%) in muscle PS, without any further effect on muscle PB. This study indicates that in PD patients in the fasting state, the moderate hyperinsulinemia that occurs during PD with dextrose alone causes an antiproteolytic action that is obscured by a parallel decrease in AA availability for PS. Conversely, the combined use of dextrose and AA results in a cumulative effect, because of the suppression of endogenous muscle PB (induced by insulin) and the stimulation of muscle PS (induced by AA availability). The hypothesis, therefore, is that in patients who are treated with PD, when fasting or when nutrient intake is reduced, muscle mass could be maintained better by the combined use of dextrose and AA.

Acute metabolic effects of dialysis fluids during CAPD

Because the osmotic agents currently used for peritoneal dialysis, ie, glucose or amino acids, are also substrates, a metabolic transfer occurs during their peritoneal absorption. After the delivery of a 3.86% glucose dialysis solution, about 100% of the glucose absorbed through the peritoneal is oxidized. So, this glucose contributes fully to the energy load of the patients. Peritoneal glucose delivery also entertains hyperglycaemia and hyperinsulinaemia as compared to oral glucose. When compared to healthy subjects, oral glucose in continuous ambulatory peritoneal dialysis (CAPD) patients induces a higher glycaemic and insulinaemic response. This traduces insulin resistance in CAPD patients even after months of that renal replacement therapy. When amino acids are used in place of glucose in dialysis solution, they stimulate whole body protein turnover and are used mainly for protein synthesis. When a meal is coingested, protein breakdown is inhibited which reinforces the positive effect of the solution on protein balance.