Rat Model Of Peritoneal Dialysis Research Articles

Long-term Intervention with Heparins in a Rat Model of Peritoneal Dialysis

Peritoneal dialysis (PD) is associated with functional and structural alterations of the peritoneal membrane, particularly new vessel formation and fibrosis. In addition to anticoagulant effects, heparin displays anti-inflammatory and angiostatic properties. Therefore, the effects of administration of heparins on function and morphology of the peritoneal membrane were studied in a rat PD model. Rats received 10 mL conventional PD fluid (PDF) daily, with or without the addition of unfractionated heparin (UFH) or low molecular weight heparin (LMWH) in the PDF (1 mg/10 mL intraperitoneally) via a mini access port. Untreated rats served as controls. After 5 weeks, a 90-minute functional peritoneal transport test was performed and tissues and peritoneal leukocytes were taken. PD treatment induced loss of ultrafiltration (p<0.01), a twofold increase in glucose absorption (p<0.03), increased urea transport (p<0.02), and loss of sodium sieving (p<0.03), which were also found in the PDF+heparin groups. Increased peritoneal cell influx and hyaluronan production (p<0.02) as well as an exchange of mast cells and eosinophils for neutrophils after PD treatment were observed in PD rats; addition of heparin did not affect those changes. Mesothelial regeneration, submesothelial blood vessel and matrix formation, and accumulation of tissue macrophages were seen in PD animals. Spindle-shaped vimentin-positive and cytokeratin-negative cells indicated either partial injury and denudation of mesothelial cells or epithelial-to-mesenchymal transition. Neither UFH nor LMWH affected any of these morphological changes. Within 5 weeks, PD treatment induces a chronic inflammatory condition in the peritoneum, evidenced by high transport, leukocyte recruitment, tissue remodeling, and induction of spindle-shaped cells in the mesothelium. Addition of LMWH or UFH to the PDF did not prevent these adverse PDF-induced peritoneal changes.

Peritoneal morphologic changes in a peritoneal dialysis rat model correlate with angiopoietin/Tie-2

The angiopoietin/Tie-2 system plays an important role in the initiation of angiogenesis. However, the role of angiopoietin/Tie-2 in peritoneal angiogenesis and fibrosis is unclear. In our study we investigated the peritoneal morphologic changes in a uremic peritoneal dialysis (PD) rat model, focusing on the relationship between angiopoietin/Tie-2 and peritoneal angiogenesis. We subjected uremic (subtotal nephrectomy) rats to dialysis, using a standard PD solution, for 10 days, 28 days, or 56 days, and compared them with uremic rats that had not undergone dialysis and control rats. Functional [dialysate-to-plasma (D/P) creatinine; ultrafiltration (UF)] and structural (vessel density and thickness of the submesothelial extracellular matrix) changes of the peritoneum were quantified. Levels of angiopoietin (Ang)-1, Ang-2, Tie-2 and vascular endothelial growth factor (VEGF) were examined in the peritoneum by real-time quantitative polymerase chain reaction (PCR) and related to angiogenesis. The uremic group that had not undergone dialysis was characterized by increased vessel density in the peritoneum compared with that of the control, which correlated with decreased UF and increased D/P creatinine. Progressive angiogenesis and fibrosis were found in the PD groups when compared with the uremic non-dialyzed or control group, accompanied by an increased D/P creatinine that occurred in the PD group after 56 days, while UF decreased. Furthermore, Ang-2 and VEGF levels increased, while Tie-2 level decreased significantly in the uremic non-dialyzed group compare with the control. This tendency was more obvious in the PD groups than in the uremic non-dialyzed or control group, but no difference was found among the PD groups. Both VEGF and Ang-2 correlated positively with vessel density, while Tie-2 correlated negatively. We confirmed angiogenesis and fibrosis changes of the peritoneum as a result of uremic status and PD therapy in the uremic PD rat model. An increased level of Ang-2 and a reduced level of Tie-2 in conditions of uremia and PD therapy correlated with peritoneal angiogenesis and functional deterioration.

New Peritoneal Dialysis Model in Rats with Bilateral Nephrectomy

Many peritoneal dialysis (PD) patients with chronic renal failure (CRF) suffer from metabolic and nutritional abnormalities. However, these abnormalities have been not sufficiently investigated. At present, the resolution of these issues in this field has been hindered by the lack of suitable PD models. We attempt to develop a rat model of PD under no constraints and under non-anesthetization to evaluate amino acid solution as suitable nutritional therapy for renal failure. In our model, bilateral nephrectomy rats were dialyzed 6 h per day for three days. The dialysate was infused and removed continually via a metering pump. Under fasting, rats were infused with 5% glucose or amino acid solution for renal failure, and they remained alive. This model can be used to examine bilateral nephrectomy in rats for three or more days. We were also able to determine protein and calorie malnutrition, negative nitrogen balance, abnormalities in the plasma amino acid pattern, and calcium and phosphorus metabolism. Thus, this model has the characteristics of renal failure in humans and may be used to easily examine the metabolic changes due to loss of kidney function.

Preservation of peritoneal morphology and function by pentoxifylline in a rat model of peritoneal dialysis: molecular studies

High-glucose (HG) content of dialysate accelerated peritoneal fibrosis. We investigated in vitro mechanisms and the in vivo potential of pentoxifylline (PTX) to prevent this fibrogenic process. For human peritoneal mesothelial cell (HPMC) culture, a normal-glucose (NG, 5.5 mM) or HG (138 mM) medium was established through pilot experiments. The rat peritoneal dialysis (PD) model consists of four groups (n = 8): group 1, intraperitoneal (IP) HG (4.25%) solution; group 2, as group 1 plus daily IP PTX (4 mg/in 1 h); group 3, IP PTX and group 4 as control. In HPMC culture, PTX significantly prevented HG-stimulated gene and protein production of collagen and transforming growth factor-beta1 (TGF-ss1) (reduction rate of 72-81%). The p38 mitogen-activated protein kinase (MAPK) pathway was activated significantly in HG-treated HPMCs. Blockade of p38 MAPK by SB203580 (25 microM) or PTX (300 microg/ml) resulted in an effective suppression of collagen and TGF-ss1 gene expression in HG-cultured HPMCs. In PD experimental animals, peritoneal thickness and collagen expression in the peritoneum were significantly increased in HG-treated rats, and was attenuated by PTX (P < 0.01). Impaired peritoneal ultrafiltration (1.9 +/- 0.5 ml versus 2.4 +/- 0.4 ml, P < 0.05) and stimulated proinflammatory IL-6, MCP-1 and TGF-beta1 activation were observed in HG-treated rats. PTX well preserved the functional characteristics of peritoneum and cytokine profiles. These in vitro and in vivo data suggest that PTX may have therapeutic benefits for the prevention or retardation of peritoneal fibrosis.

The Role of the TGF/Smad Signaling Pathway in Peritoneal Fibrosis Induced by Peritoneal Dialysis Solutions

Background: Peritoneal dialysis (PD) solutions contribute to peritoneal membrane damage. We investigated how conventional and biocompatible PD solutions with different glucose concentrations affect morphological and functional signs of peritoneal fibrosis as well as the TGF-β1/Smad signaling pathway in a chronic PD rat model. Methods: Non-uremic male Wistar rats (n = 28) were dialyzed thrice daily for 28 days with 20 ml of a conventional solution (Dianeal® 1.36%, D1, or 3.86%, D3) or a biocompatible solution (Physioneal® 1.36%, P1, or 3.86%, P3). A peritoneal equilibration test was performed. Six rats without dialysis served as controls. Results: The use of conventional solutions, particularly D3, resulted in expansion of the submesothelial compact zone, loss of mesothelial cell layer integrity, hypercellularity, accumulation of collagen I, increased vessel numbers and increased TGF-β1/Smad expression, but this did not significantly change fluid and solute peritoneal transport characteristics. In comparison with D1 and D3, the use of P1 and P3 was associated with less TGF-β1/Smad expression and less expansion of the submesothelial cell layer. Conclusions: Our findings indicate that biocompatible solutions with less glucose may decrease the rate of peritoneal fibrosis. The TGF-β1/Smad pathway is stimulated by PD solutions, representing a plausible pathophysiological mechanism.

ACE Inhibitor and At1-Receptor Blocker Attenuate the Production of Vegf in Mesothelial Cells

Human mesothelial cells (HMC) are a major source of intraperitoneal vascular endothelial growth factor (VEGF) and by that are presumably involved in complications of long-term peritoneal dialysis (PD), such as ultrafiltration failure. This prompted us to look for agents that reduce basic mesothelial VEGF production and abrogate VEGF-overproduction induced by proinflammatory cytokines such as tumor necrosis factor alpha (TNF-alpha) and interleukin-1alpha (IL-1alpha). Angiotensin-converting enzyme (ACE) inhibition was found to preserve peritoneal function and ameliorate morphologic changes in a rat PD model. The present in vitro study was designed to investigate the effect of the ACE inhibitors captopril and enalapril, and the angiotensin II type 1-receptor (AT1) antagonist losartan on mesothelial VEGF synthesis. HMC were isolated from omental tissue and taken into culture. VEGF antigen concentrations were measured in the cell supernatant by ELISA. VEGF mRNA levels were determined by real-time polymerase chain reaction. Incubation of HMC with captopril (100-1000 micromol/L) resulted in a concentration-dependent attenuation of VEGF synthesis. Incubation with captopril (500-1000 micromol/L), enalapril (100-1000 micromol/L), and losartan (1-100 micromol/L) significantly decreased inflammatory mediator (TNF-alpha, IL-1alpha)-induced mesothelial VEGF overproduction. The results indicate that ACE inhibitors and AT1-receptor blockers are capable of effectively attenuating the overproduction of VEGF due to proinflammatory cytokine stimuli. These data suggest that locally produced angiotensin II in the peritoneal cavity may be a potential therapeutic target in ultrafiltration failure during longterm PD.

Peroxisome Proliferator-Activated Receptor-γ Agonists Diminish Peritoneal Functional and Morphological Changes Induced by Bioincompatible Peritoneal Dialysis Solution

Background: To evaluate if peroxisome proliferator-activated receptor-γ (PPAR-γ) agonists have a potential protective effect on the peritoneum changes induced by bioincompatible peritoneal dialysis (PD) solution in vivo. Methods: Male Wistar rats were dialyzed three times daily for 28 days with 1.36% Dianeal® (two groups: with (D+R) or without (D) rosiglitazone) or 1.36% Physioneal® (two groups: with (P+R) or without (P) rosiglitazone). Peritoneal transport of fluid and small solutes was assessed. Nine rats that did not receive dialysis served as controls. Results: Significant morphological changes were found in the D group compared with controls. Additional use of rosiglitazone in the D+R group resulted in less morphological changes and expression of collagen I as well as an increased drainage volume. The expression of VEGF was inhibited by rosiglitazone while no apparent effect was found regarding TGF/Smad pathway. Conclusions: The addition of rosiglitazone to standard dialysis fluids can maintain the peritoneal morphology and increase ultrafiltration in a PD rat model.

Antibiotic Prophylaxis in an Animal Model of Chronic Peritoneal Exposure

Acute infection in an animal model of chronic peritoneal dialysis (PD) induces structural changes in the peritoneum and altersfunctional characteristics of transport. These changes may compromise observations of the chronic effects of dialysis solutions. To test the hypothesis that antibiotics would prevent acute infection without affecting transport and structural properties, we characterized the frequency of infection in our rat model of PD and examined whether the inclusion of antibiotics in the dialysis solution altered the transport and structural properties of the peritoneum. Female Sprague-Dawley rats were aseptically injected daily under gas anesthesia with 30 - 40 mL of a sterile solution for 2 months via a peritoneal catheter tunneled to a subcutaneous port. Solutions used were Krebs-Ringer bicarbonate (KRB) alone, KRB with antibiotics (cefazolin 200 mg/L and gentamicin 2 mg/L), KRB with 4% glucose, and KRB with both glucose and antibiotics. After 2 months, osmotic filtration andsolute transport were assessed in each animal and peritoneal fluid was collected for bacterial culture. Angiogenesis was evaluated by quantitative image analysis of tissue sections stained with CD31. Tissue content of collagen, hyaluronic acid, and sulfated glycosaminoglycan was determined. Technique survival (successful PD for 2 months) and infection rate were comparable among all treated groups. There were no differences between the groups in transport properties. Structural changes were comparable between groups, with or without antibiotics. Addition of antibiotics to the dialysis solution did not affect thetransport characteristics of the peritoneum or the pathologic reaction of the tissue to the PD solution.

Beneficial effects of aminoguanidine on peritoneal microcirculation and tissue remodelling in a rat model of PD

The formation of glucose degradation products (GDPs) and accumulation of advanced glycation end products (AGEs) partly contribute to the bioincompatibility of peritoneal dialysis fluids (PDF). Aminoguanidine (AG) scavenges GDPs and prevents the formation of AGEs. In a peritoneal dialysis (PD) rat model, we evaluated the effects of the addition of AG to the PDF on microcirculation and morphology of the peritoneum, by intravital microscopy and quantitative morphometric analysis. AG-bicarbonate effectively scavenged different GDPs from PDF. Daily exposure to PDF for 5 weeks resulted in a significant increase in leucocyte rolling in mesenteric venules, which could be reduced for approximately 50% by addition of AG-bicarbonate (P<0.02). Vascular leakage was found in rats treated with PDF/AG-bicarbonate, but not with PDF alone. Evaluation of visceral and parietal peritoneum showed the induction of angiogenesis and fibrosis after PDF instillation. PDF/AG-bicarbonate significantly reduced vessel density in omentum and parietal peritoneum (P<0.04), but not in mesentery. PDF-induced fibrosis was significantly reduced by AG (P<0.02). PDF instillation led to AGE accumulation in mesentery, which was inhibited by supplementation of AG. Since addition of AG-bicarbonate to PDF raised pH from 5.2 to 8.5, a similar experiment was performed with AG-hydrochloride that did not change the fluid acidity. We could reproduce most of the results obtained with AG-bicarbonate; however, AG-hydrochloride induced no microvascular leakage and had a minor effect on angiogenesis. The supplementation of either AG reduced a number of PDF-induced alterations in our model, emphasizing the involvement of GDPs and/or AGEs in the PDF-induced peritoneal injury.

Functional and molecular characterization of a peritoneal dialysis model in the C57BL/6J mouse

Animal models are important for understanding the physiology and pathophysiology of peritoneal transport during peritoneal dialysis (PD). Mechanistic investigations of rat and rabbit models of PD are mostly based on intervention studies using pharmacologic agents or blocking antibodies. These models may be limited by the time-course, lack of specificity, or side effects of such interventions. Genetically modified mice could provide an attractive alternative to the above models. In this study, we have characterized PD parameters and tested the effect of gender and dialysate volume and/or osmolality in the C57BL/6J mouse. Mice were submitted to a 2-hour peritoneal equilibration test in order to obtain permeability parameters. The expression of the water channel aquaporin-1 (AQP1) and endothelial NO synthase (eNOS) was investigated at the protein (immunoblotting, immunostaining) and mRNA [real-time reverse-transcription-polymerase chain reaction (RT-PCR)] levels. The potential effect of gender on these parameters was also studied. Exposure of mice to 2 mL of 3.86% glucose dialysate yielded equilibration curves for urea and glucose, a sodium sieving, and a net ultrafiltration (UF) that were remarkably similar to those obtained in rats. The increase in dialysate volume (from 2 mL to 3 mL and 6 mL) resulted in a higher ultrafiltration and, for the highest volume, an increase in the diffusive mass transport coefficient (MTAC) for urea. The increase in dialysate glucose concentration (from 1.36% to 3.86% and 7%) resulted in increased sodium sieving and higher UF, whereas the MTAC for urea was unchanged. In comparison with males, females had a similar peritoneal transport rate for small solutes but a significantly lower sodium sieving, reflecting a lower AQP1 mRNA and protein expression in the peritoneum. These data demonstrate the structural and functional similarity between mouse and rat models of PD, and further emphasize the relevance of mouse models to understand PD in humans. They also suggest that gender may influence water transport and AQP1 expression in the peritoneum.

Immunopathological changes in a uraemic rat model for peritoneal dialysis

Peritoneal dialysis (PD) is a treatment modality for patients with renal failure. Both the uraemic state of these patients and chronic exposure to PD fluid are associated with the development of functional and structural alterations of the peritoneal membrane. In a well-established chronic PD rat model, we compared rats with normal renal function with subtotal nephrectomized rats that developed uraemia. Uraemic and control rats received daily 10 ml conventional glucose containing PD fluid, via peritoneal catheters during a 6 week period. Uraemic and control rats receiving no PD fluid served as controls. Parameters relevant for peritoneal defence and serosal healing responses were analyzed. Uraemic animals were characterized by 2-3-fold increased serum urea and creatinine levels, accompanied by a significantly reduced haematocrit. Uraemia (without PD fluid exposure) induced new blood vessels in different peritoneal tissues, accompanied by increased accumulation of advanced glycation end products (AGEs) and elevated levels of angiogenic factors such as vascular endothelial growth factor and monocyte chemoattractant protein-1 (MCP-1) in peritoneal lavage fluid. A much stronger peritoneal response was observed upon PD fluid exposure in non-uraemic rats. This included the induction of angiogenesis and fibrosis in various peritoneal tissues, accumulation of AGEs, immunological activation of the omentum, damage to the mesothelial cell layer, focal formation of granulation tissues and increased MCP-1 and hyaluronan levels in peritoneal lavage fluid. Finally, chronic PD fluid instillation in uraemic rats did not induce an additional peritoneal response compared to PD fluid exposure in non-uraemic rats, except for the degree of AGE accumulation. Both uraemia and PD fluid exposure result in pathological alterations of the peritoneum. However, uraemia did not induce major additive effects to PD fluid-induced injury. These results substantially contribute to the understanding of the pathobiology of the peritoneum under PD conditions.

Effects of Intraperitoneal Hyaluronan on Peritoneal Fluid and Solute Transport in Peritoneal Dialysis Patients

Hyaluronan (HA) is a glycosaminoglycan found in connective tissues and tissue spaces, including the peritoneal cavity. In vivo studies in a rat model of peritoneal dialysis (PD) have shown that addition of HA to PD solution during an intraperitoneal dwell can alter peritoneal fluid transport and protect the peritoneal membrane from the effects of inflammation and repeated infusions of dialysis solution. The current study sought to evaluate the safety of intraperitoneal HA and its effect on peritoneal fluid and solute transport when administered during a dialysis dwell in humans. 13 PD patients were enrolled in a prospective, randomized crossover study involving three dialysis treatments using the following PD solutions: (1) a commercially available PD solution (Dianeal PD-4, 1.36% glucose; Baxter Healthcare Corporation, Alliston, Ontario, Canada); (2) Dianeal PD-4 containing 0.1 g/L HA, and (3) Dianeal PD-4 containing 0.5 g/L HA. Each 6-hour dialysis exchange was separated from the other exchanges by a 2-week washout period. Radioiodinated human serum albumin (RISA) was administered with the dialysis solution to evaluate intraperitoneal volume, net ultrafiltration (UF), and fluid reabsorption. Peritoneal clearances, dialysate/plasma ratios (D/P), and mass transfer area coefficients (MTACs) were determined for sodium, urea, creatinine, albumin, and glucose. Safety was evaluated by monitoring adverse events and changes in serum chemistries. Ten patients completed all three dialysis exchanges and two additional patients completed at least one treatment exchange. There were no reported adverse events related to HA administration and no significant changes in serum chemistries. There were no significant differences in net UF or peritoneal volume profiles among the three treatments. Mean net UF calculated using residual volumes, estimated by RISA dilution, tended to be slightly higher during treatment with solution containing 0.1 g/L HA and 0.5 g/L HA [74 +/- 86 (SE) and 41 +/- 99 mL, respectively] compared to control treatment (-58 +/- 129 mL). Although not statistically significant, there was a trend toward decreased fluid reabsorption during treatment with HA. Solute clearances, D/P ratios, and MTACs were similar for the three treatments. Serum levels of HA were also unaffected by the two treatment solutions. These data support the acute safety of HA when administered intraperitoneally with the dialysis solution to PD patients. Due to the small sample size and variability in net UF and fluid reabsorption, statistically significant differences were not demonstrated for these parameters. However, a trend toward decreased fluid reabsorption was observed, suggesting that HA may act by a mechanism similar to that observed in animal studies. Further studies are necessary to evaluate whether the beneficial effects of HA observed in animal studies can be shown in humans.

Influence of Neutral-Ph Dialysis Solutions on the Peritoneal Membrane: A Long-Term Investigation in Rats

Glucose degradation products (GDPs) and low pH are potential causes of bioincompatibility of peritoneal dialysis fluids (PDFs). The aim of the present study was to compare the effect of 6 weeks' exposure of the peritoneum in rats to two different PDFs: a standard PDF with a low pH and high level of GDPs (CAPD 3: Fresenius Medical Care, Bad Homburg, Germany), and a modified PDF with a low level of GDPs and a physiologic pH (CAPD 3 Balance: Fresenius Medical Care). After catheter implantation, rats were exposed twice daily for 6 weeks to CAPD 3 fluid or to CAPD 3 Balance. At the beginning and at the end of the study, a 4-hour dwell was performed in every rat to evaluate intraperitoneal inflammation and its effect on total collagen synthesis in the in vitro cultured rat mesothelial cells (ex vivo study). Additionally, after 6 weeks' exposure, the peritoneal cavity was opened, and macroscopic changes were evaluated according to a semiquantitative scale. Peritoneal samples were also taken for morphology study. In rats treated with CAPD 3 fluid, intraperitoneal inflammation was comparable at the beginning and at the end of the experiment. In animals exposed to CAPD 3 Balance, the intensity of the intraperitoneal inflammation decreased during the study (cell count, p = 0.0781; neutrophil:macrophage ratio, p < 0.01; nitrite concentration, p < 0.05; hyaluronan level, p < 0.05). The capacity of effluent dialysate from CAPD 3 rats to activate collagen synthesis in in vitro-cultured mesothelial cells was the same at the beginning and at the end of the study. In the CAPD 3 Balance group, this capacity was statistically significantly lower at the end of the study than at the beginning (p < 0.05). The mean thickness of the visceral peritoneum was comparable in both groups of animals, but, macroscopically, more severe fibrosis was found in the peritoneum of rats exposed to CAPD 3 as compared with animals treated with CAPD 3 Balance (p < 0.05). We showed that, in the rat model of peritoneal dialysis, chronic exposure of the peritoneum to PDFs with low GDPs and a physiologic pH diminished the intraperitoneal inflammatory reaction induced by dialysis, and reduced peritoneal fibrosis.

Effect of PD fluid instillation on the peritonitis-induced influx and bacterial clearing capacity of peritoneal cells.

The commonly used peritoneal dialysis fluids contain glucose as the osmotic agent. Heat sterilization leads to the formation of glucose degradation products which contribute, together with glucose, to the formation of advanced glycation end-products (AGEs). AGEs have been shown to be present in the peritoneal cavity. Methods have been developed to minimize the amount of glucose degradation products in peritoneal dialysis fluids. In a rat peritoneal dialysis model, we compare the effect of a commonly used peritoneal dialysis fluid, Gambrosol, with a newly developed peritoneal dialysis fluid, PD-Bio, on the influx and functional capacity of the peritoneal cells after 2 weeks of peritoneal dialysis fluid instillation. Three groups of animals were used: rats received daily infusion with 15 ml of either 4% Gambrosol (group 1) or 4% PD-Bio (group 2), and a control group of animals did not receive fluid (group 3). After 2 weeks of PD fluid instillation, all the animals were injected with a 0.5 ml suspension containing 3x10(8) colony-forming units of Staphylococcus aureus. The in vivo bacterial clearing capacity was determined after 15 h. A statistically significant higher leukocyte influx was found in the control group compared with both PD fluid-injected groups. No statistical differences in bacterial clearing were observed among the three groups, although the number of bacteria recovered from the PD-Bio group tended to be lower than that from the Gambrosol group. Moreover, in both PD fluid instillation groups, the bacteria tended to be cleared more slowly compared with the control group. The number of mesothelial cells in the PD fluid groups was significantly greater than in the control group. No differences were observed in bacterial clearing capacity, leukocyte influx and mesothelial cell number after a 2 week exposure of the peritoneal cavity to Gambrosol vs PD-Bio.

Effect of Fluid Supplementation and Modality on Peritoneal Permeability Characteristics in a Rat Peritoneal Dialysis Model

Hemoconcentration may influence peritoneal permeability parameters in anesthetized animals without fluid supplementation. Therefore, the aim of this study was to investigate the effects of fluid supplementation on peritoneal permeability in an acute peritoneal dialysis model in anesthetized rats. To study the effect of fluid supplementation on peritoneal permeability characteristics, 24 anesthetized male Wistar rats were investigated in 3 groups during a 4-hour standardized peritoneal permeability analysis with a 3.86% glucose dialysis solution (SPARa). The groups included a control group with no fluid supplementation (None, n = 8), a group with continuous subcutaneous infusion of 0.9% NaCl 3 mL/hr (SC, n = 9), and a group with continuous intravenous infusion of 0.9% NaCl 3 mL/hr (IV, n = 7). Inflow, sampling, and outflow of the dialysate during the SPARa occurred via a cannula inserted intraperitoneally in the lower left quadrant of the abdomen. Blood was drawn at the end of the dwell. Baseline blood samples were obtained from six separate untreated rats. Plasma osmolality was significantly lower in the IV group (334+/-1.4 mOsm/kg) compared to the None group (348+/-0.7 mOsm/kg, p < 0.01), and not different from the SC group (335+/-6.4 mOsm/kg), but higher than baseline (314+/-5.3 mOsm/kg, p < 0.001). Urine production during the dwell was not different among the groups: None 10.6+/-5.3 mL; SC 8.0+/-6.0 mL; and IV 10.5+/-5.6 mL. Transcapillary ultrafiltration after 4 hours was significantly higher in the IV group (p < 0.05) compared to the other two groups. Net ultrafiltration and effective lymphatic absorption were similar in all groups. Mass transfer area coefficient of urea (MTACurea) was significantly greater in the IV group (155+/-23.2 microL/minute, p < 0.003), but not different between the None (118+/-16.2 microL/min) and SC (123+/-25.9 microL/min) groups. Correcting these for the baseline plasma concentration resulted in higher values, but the IV data remained greater than the SC and None groups (p < 0.01). The glucose absorption, albumin, and IgG clearances and the sieving of sodium were alike in all groups. It can be concluded that IV fluid supplementation is more effective in preventing dehydration than SC supplementation, and it enhanced some peritoneal permeability characteristics in anesthetized rats during a 4-hour investigation. It is therefore important to standardize fluid supplementation in experiments with anesthetized animals.

Very High Daily Intraperitoneal Doses of Carbonyl Compounds Affect the Morphology, but Not the Exchange Characteristics, of Rat Peritoneum

Glucose degradation products (GDP) are carbonyl compounds, that are formed by heat sterilization of conventional peritoneal dialysis (PD) fluids. Carbonyl compounds are known to be toxic in vitro and potentially toxic also in vivo. The aim of this study was to evaluate the effects of daily, short-term exposure of the peritoneum to very high concentrations of GDP in vivo on peritoneal transport parameters and on peritoneal morphology in a well-established rat model of PD. Rats were exposed to three daily intraperitoneal (IP) injections (10 ml) for 9 days of a largely neutral (pH 7.2) PD fluid containing 1.5% glucose and sterilized by filtration, with (n = 8) or without (n = 8) the presence of different carbonyl compounds in concentrations 100 times higher than those reported in commercial PD fluids. Seven rats, not subjected to any exposure, served as controls. After the exposure, the rats were subjected to acute PD in 4-hour dwells. Twenty milliliters of 4% glucose dialysis fluid were instilled into the rat peritoneal cavity. Blood and dialysate samples were taken during the dwell for measurements of dialysate sodium, and for assessments of the mass transfer area coefficient (PS) for glucose and ⁵¹Cr-EDTA and of transperitoneal clearance (Cl) or radiolabelled albumin (RISA). At the end of the dwell, parts of the liver, diaphragm and peritoneum were removed for measurements of tissue cell density and thickness of the submesothelial peritoneal tissue. The exposure of the peritoneum to very high doses of carbonyl compounds did not affect the peritoneal transport of fluid and small solutes significantly, but seemed to slightly reduce lymph flow and albumin clearance out of the peritoneal cavity. Assessed after a hypertonic dwell, and compared to the situation in nontreated rats after the same kind of dwell, there was a significant thinning of the submesothelial tissue, but no difference in tissue cell density. It is concluded that short-term exposure of the peritoneum in vivo to very high doses of GDP resulted in almost no signs of acute toxicity.

Peritoneal Accumulation of Advanced Glycosylation End-Products in Diabetic Rats on Dialysis with Icodextrin

To evaluate and compare the effects of glucose-based solutions to those of icodextrin with respect to peritoneal transport characteristics and formation of advanced glycosylation end-products (AGEs) in the peritoneal membrane in the diabetic rat model of peritoneal dialysis (PD). Thirty-three male Sprague-Dawley rats weighing between 275 - 300 g were divided into 5 groups: group C (n = 6), control rats with catheter but not dialyzed; group D (n = 5), diabetic rats with catheter but not dialyzed; group G (n = 7), diabetic rats dialyzed with standard 2.5% glucose solution for daytime exchanges and 4.25% glucose solution for the overnight exchange; group H (n = 8), diabetic rats dialyzed with standard 2.5% glucose solution for daytime exchanges and 7.5% icodextrin solution for overnight exchanges; group I (n = 7), diabetic rats dialyzed with 7.5% icodextrin solution for all exchanges. Dialysis exchanges were performed three times daily with an instillation volume of 25 mL per exchange for a period of 12 weeks. Tissue sections were stained using a monoclonal anti-AGE antibody. One-hour peritoneal equilibration tests (PET) were performed every 4 weeks for comparison of transport characteristics. The level of immunostaining was lowest in group C and highest in group G. Significant differences were seen between group C and groups G, H, and I (p < 0.001, p = 0.001, and p< 0.05 respectively). Significant differences were also found between group G and groups D and I (p < 0.05 and p < 0.05 respectively). Over time, glucose concentration at the end of an exchange versus concentration at instillation (D/D0 glucose) decreased and dialysate-to-plasma ratio (D/P) of urea increased. Significant differences were found between groups C and H for D/D0 glucose (0.40+/-0.01 vs 0.35+/-0.01, p < 0.05); and between groups C and H for D/P urea (0.87+/-0.03 vs 0.97+/-0.02, p < 0.05). These results suggest that AGE formation is lower with the use of peritoneal dialysis solution containing icodextrin than with glucose-based solutions. We conclude that the use of icodextrin may be helpful in slowing the deterioration of the peritoneal membrane, prolonging its use for dialysis.

Advanced Glycosylation End-Products in Diabetic Rats on Peritoneal Dialysis Using Various Solutions

To evaluate and compare the effects of glucose-based solutions to those of icodextrin with respect to peritoneal transport characteristics and advanced glycosylation end-product (AGE) formation in the peritoneal membrane in a diabetic rat model of peritoneal dialysis (PD). Thirty-three male Sprague-Dawley rats weighing between 275-300 g were divided into five groups: group C (n = 6), control rats implanted with a catheter but not dialyzed; group D (n = 5), diabetic rats implanted with a catheter but not dialyzed; group G (n = 7), diabetic rats implanted with a catheter and dialyzed with standard 2.5% glucose solution for daytime exchanges and 4.25% glucose solution for overnight exchanges; group H (n = 8), diabetic rats implanted with a catheter and dialyzed with standard 2.5% glucose solution for daytime exchanges and 7.5% icodextrin solution for overnight exchanges; group I (n = 7), diabetic rats implanted with a catheter and dialyzed with 7.5% icodextrin solution for all exchanges. Dialysis exchanges (25 mL per exchange) were performed three times daily for a period of 12 weeks. Tissue sections were stained using a monoclonal anti-AGE antibody. One-hour peritoneal equilibration tests (PET) were performed every 4 weeks for comparison of transport characteristics. The level of immunostaining was lowest in group C and highest in group G. Significant differences in immunostaining were seen between group C and group G (p < 0.001), group C and group H (p = 0.001), and group C and group I (p < 0.05). Significant differences were also found between group G and group D (p < 0.05), and between group G and group I (p < 0.05). Over time, the ratio of glucose concentration after 1 hour to glucose concentration at instillation (D/D0) decreased and the dialysate-to-plasma ratio (D/P) of urea increased. Significant differences in D/D0 glucose and D/P urea were found between group C and group H (D/D0: 0.40 +/- 0.01 vs 0.35 +/- 0.01, p < 0.05; D/P urea: 0.87 +/- 0.03 vs 0.97 +/- 0.02, p < 0.05). These results suggest that AGE formation is lower with the use of peritoneal dialysis solution containing icodextrin than with glucose-based solution. We conclude that use of icodextrin may help to slow the deterioration of the peritoneal membrane, prolonging its use for dialysis.

Effects of Peritoneal Rest on Peritoneal Transport and Peritoneal Membrane Thickening in Continuous Ambulatory Peritoneal Dialysis Rats

To evaluate the effects of peritoneal rest on peritoneal transport and morphology in a rat model of peritoneal dialysis. Twenty-four rats (Sprague-Dawley, male, 250-300 g) were divided into three groups: group 1 (control, n = 6) without dialysis, group 2 (n = 9) sacrificed immediately after 3 weeks of dialysis, and group 3 (n = 9) sacrificed after 4 weeks of peritoneal rest after 3 weeks of dialysis. Both dialysis groups were dialyzed twice daily with an intraperitoneal instillation volume of 25 mL of 3.86% dextrose solution for 3 weeks. Peritonitis was induced by supplementing the dialysis fluid with lipopolysaccharide (5 microg/mL) on days 8, 10, and 12 in both dialysis groups. Peritoneal equilibration tests were performed on each animal at baseline. The equilibration tests were repeated at the 4th and the 8th week of dialysis. Morphometric analyses of the peritoneal membrane were carried out in tissue specimens obtained at the time of sacrifice. The D/D0 ratio for glucose at two hours in groups 2 and 3 at the beginning of week 4 was significantly lower than at baseline, indicating an increase in peritoneal permeability to glucose after 3 weeks of dialysis. D/D0 in group 3 at the beginning of week 8, after 4 weeks of peritoneal rest, was significantly higher than at week 4. The drain volume in groups 2 and 3 at week 4 was significantly lower than at baseline; however, the drain volume in group 3 at week 8 was significantly higher than at week 4. The thickness of the parietal peritoneal membrane in group 3 was significantly greater than in group 1 and less than in group 2 (group 1, 11.4+/-7.6 microm; group 2, 37.5+/-18.4 microm; group 3, 21.4+/-12.1 microm). Peritoneal rest improves ultrafiltration in rats by decreasing the hyperpermeability of glucose and also reduces the degree of peritoneal thickening. These data suggest that dialysis-induced changes in peritoneal transport and morphology are reversible under the conditions of peritoneal rest in this experimental model.

Expected White Blood Cell Counts and Differentials in a Rat Model of Peritoneal Dialysis

The purpose of this study was to establish baseline dialysate white blood cell (WBC) counts and differentials in noninfected rats on peritoneal dialysis (PD). Sixteen male Sprague-Dawley rats underwent PD in the first protocol, and eight from the 16 continued PD in the second through fourth protocols. At the beginning of the experiments, all animals had a PD catheter implanted and were initiated on PD with 1.5% dextrose dialysis solution twice daily. In the first protocol, WBC counts and differentials were assessed from day 4 to day 15 of dialysis in noninfected animals to establish "normal values" for such a rat model. In protocol 2, WBC counts and solute concentrations in small aliquots of dialysate obtained from the catheter were compared to values in well-mixed total drainage. Protocol 3 was designed to assess effects of dwell time on WBC counts. Protocol 4 examined the effect of glucose concentration of dialysis solution on WBC counts. In the first protocol, the mean dialysate WBC counts were significantly higher on the fourth day of dialysis, but stabilized below 2500 cells/mm3 by the eighth day. The percentage of neutrophils was stable around 20%-25%. In the second protocol, we found aliquots < 1 mL might underestimate the dialysate WBC count compared to the complete drainage. In the third protocol, WBC counts increased as cycle time became longer, but the percentage of neutrophils remained below 50%. In the fourth protocol, we did not find any effects of glucose concentration of instilled solutions on WBC counts and differentials. This study of WBC counts and differentials in noninfected rats on peritoneal dialysis establishes the range above which infection should be suspected. WBC counts increase with cycle time. Small dialysate aliquots may underestimate WBC counts. Glucose concentration does not effect WBC counts.