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Background: A long-term peritoneal exposure model has been developed in Wistar rats. Chronic daily exposure to 3.86% glucose based, lactate buffered, conventional dialysis solutions is possible for up to 20 weeks and induces morphological abnormalities similar to those in long-term peritoneal dialysis (PD) patients. The possible effects of kidney failure in this model are unknown. The aim was to analyze the effects of chronic kidney failure on peritoneal function and morphology, alone and in combination with PD exposure, in a well-established, long term, peritoneal exposure model in the rat. ♢, Methods: 40 male Wistar rats were randomly assigned into four experimental groups: no nephrectomy, no peritoneal exposure (sham; n = 8); nephrectomy, no peritoneal exposure (Nx; n = 12); no nephrectomy, with peritoneal exposure (PD; n = 8); and nephrectomy, with peritoneal exposure (NxPD; n = 12). The nephrectomy consisted of a one-step 70% nephrectomy. The peritoneal exposure groups were infused once daily for 16 weeks with a 3.86% glucose-based dialysis solution. Development of chronic kidney disease was monitored during the experiment. Peritoneal function and morphological assessment of the peritoneal membrane were performed at the end of the experiment. ♢, Results: During follow-up the nephrectomized groups developed uremia with remarkable renal tubular dilatation and glomerular sclerosis in the renal morphology. Functionally, uremia (Nx) and PD exposure (PD) alone showed faster small solute transport and a decreased ultrafiltration capacity, which were most pronounced in the combination group (NxPD). The presence of uremia resulted in histological alterations but the most severe fibrous depositions and highest vessel counts were present in the PD exposure groups (PD and NxPD). Significant relationships were found between the number of vessels and functional parameters of the peritoneal vascular surface area. ♢, Conclusion: It is possible to induce chronic kidney failure in our existing long-term peritoneal infusion model in the rat. The degree of impairment of kidney function after 16 weeks is comparable to chronic kidney disease stage IV. Uremia per se induces both functional and morphological alterations of the peritoneal membrane. An additive effect of these alterations is present with the addition of chronic kidney failure to the model. The latter makes the present long-term model important in better understanding the pathophysiology of the peritoneal membrane in PD.

Background: Long-term peritoneal dialysis (PD) with conventional glucose based, lactate-buffered PD fluids may lead to morphological and functional alterations of the peritoneal membrane. It was hypothesized that long-term exposure to a different buffer and a mixture of osmotic agents would cause less peritoneal abnormality., Objectives: To investigate the effects of long-term exposure to a bicarbonate/lactate-buffered dialysis solution with a mixture of osmotic agents: glycerol 1.4%, amino acids 0.5%, and dextrose 1.1% (= 1% glucose) (GLAD) in a rat model with chronic kidney failure., Methods: All rats underwent a peritoneal catheter implantation and a 70% nephrectomy. Thereafter, the rats were randomly divided into 3 groups: GLAD, 3.86% Dianeal (Baxter, Nivelles, Belgium), and buffer (Physioneal without glucose, Baxter). All rats were infused daily for 16 weeks with the appropriate PD fluid. Afterwards, a peritoneal permeability analysis (SPARa) was performed using 3.86% Physioneal in all groups. After the SPARa, the rats were sacrificed to obtain tissue samples for morphometric determinations. Omental tissue was stained with picro Sirius red for assessment of fibrosis and with CD31 for vessel density., Results: GLAD and Dianeal showed faster small solute transport compared to the hypotonic buffer. No differences between the groups were present in ultrafiltration. Dianeal had the lowest value for free water transport and the highest protein clearances. Total triglyceride in plasma was not different between GLAD and the buffer. Vessel density after GLAD exposure (20 V/F) was very similar to the value found for the buffer solution (17 V/F); Dianeal caused a significantly higher value (35 V/F, p < 0.01). Also, the amount of fibrosis was higher in the Dianeal-exposed rats (p < 0.01)., Conclusion: Both hypertonic dialysis solutions increased peritoneal solute transport. GLAD exposure was associated with the best preservation of peritoneal morphology. The results of GLAD were very similar to those of the bicarbonate/lactate-buffered solution without osmotic agents. Studies in humans are needed for further assessment of GLAD.

Biocompatible dialysis solutions have been developed to preserve peritoneal membrane morphology and function. Compared with a conventional solution, a combination of glycerol, amino acids, and dextrose in a bicarbonate/lactate buffer (GLAD) led to less peritoneal fibrosis and fewer vessels in a chronic peritoneal exposure model in the rat. However, no concomitant reduction in small-solute transport was observed. We hypothesized that this result could be attributable to peritoneal vasodilation induced by vasoactive substances such as nitric oxide. The aim of the present study was to investigate whether fast transport of small solutes and proteins induced by exposure to GLAD could be influenced by Ngamma -methyl-L-arginine acetate (L-NMMA), an inhibitor of NO. These investigations used our rat model of long-term peritoneal exposure with chronic renal failure. All rats underwent peritoneal catheter implantation and a 70% nephrectomy. Thereafter, the rats were allocated to 3 groups: 16 weeks of peritoneal exposure to GLAD and L-NMMA, to GLAD only, or to buffer (bicarbonate/lactate without any osmotic agent). Afterward, a standard peritoneal permeability analysis adjusted for the rat was performed. Subsequently, the rats were euthanized, and tissue samples were obtained for morphometric determinations. No effect of L-MNNA on the transport of small solutes and proteins was found. Also, no effect on morphology was found. Our findings make it unlikely that NO is directly involved, being more in favor of a direct effect of amino acids on peritoneal transport.

Background: Conventional lactate-buffered peritoneal dialysis (PD) fluids containing glucose and glucose degradation products are believed to contribute to the development of fibrosis and angiogenesis in the dialyzed peritoneum. To reduce potential negative effects of lactate, pyruvate was substituted as a buffer and its effects on peritoneal pathological alterations were studied in a chronic peritoneal exposure model in the rat., Methods: 20 Wistar rats were infused intraperitoneally with pyruvate-buffered (n = 9) or lactate-buffered PD fluid. After 20 weeks of daily infusion, peritoneal function was assessed. In omental peritoneal tissue, the number of blood vessels was analyzed following alpha-smooth muscle actin staining. The degree of fibrosis was quantitated in Picro Sirius Red-stained sections and by assessment of the hydroxyproline content. Plasma lactate/pyruvate and betahydroxybutyrate/acetoacetate (BBA/AA) ratios were determined. Plasma and dialysate vascular endothelial growth factor (VEGF) levels were quantitated by ELISA., Results: The mass transfer area coefficient of creatinine was higher and the dialysate-to-plasma ratio of sodium was lower in pyruvate-treated animals compared to the lactate-treated group (0.11 vs 0.05 mL/min, p < 0.05, and 78% vs 89%, p < 0.05). The BBA/AA ratio tended to be lower in the pyruvate animals (p = 0.07). The number of blood vessels was lower in pyruvate-treated animals (16 vs 37 per field, p < 0.001). Total surface area, luminal area, and wall/total area of the vessels were larger in the pyruvate group. The degree of fibrosis was lower in intersegmental and perivascular areas of pyruvate-exposed animals. Effluent VEGF was higher in the pyruvate group., Conclusions: Replacement of lactate by pyruvate resulted in changes in peritoneal solute transport, accompanied by a reduction in both peritoneal membrane angiogenesis and fibrosis, suggesting potentially novel mechanisms to reduce glucose-driven alterations to the peritoneal membrane in PD patients.

Background: Long-term peritoneal dialysis may lead to peritoneal membrane failure. Loss of ultrafiltration is the most important clinical abnormality. Loss of ultrafiltration is associated with an increased number of peritoneal blood vessels, with fibrotic alterations, and with loss of mesothelium. Continuous exposure to bioincompatible dialysis solutions is likely to be important in the pathogenesis of these alterations., Methods: This article reviews the toxicity of various constituents of dialysate, current assessments of interventions, and the results of interventions aimed at preserving the peritoneum., Results: Glucose, possibly in combination with lactate, and glucose degradation products (GDPs) are likely to be the most toxic constituents of dialysate. Diabetiform peritoneal neoangiogenesis is likely to be mediated by vascular endothelial growth factor (VEGF). Release of VEGF might be influenced by glucose-induced cellular pseudohypoxia, which is likely to be increased by exposure to lactate. Glucose and GDPs are both toxic to peritoneal cells. Glucose degradation products induce the formation of advanced glycosylation end-products at a much faster rate than does glucose itself, but the relative importance of GDPs and glucose in clinical PD has not been clarified. The effects of interventions should first be assessed in long-term animal models, followed by clinical studies on peritoneal transport and on effluent markers that may reflect the status of the peritoneum. Possible interventions aim at reducing peritoneal exposure to glucose, GDPs, and lactate. Techniques include peritoneal resting, replacing some glucose-based exchanges with amino acid-based and icodextrin-based dialysate, using bicarbonate as a buffer, and administering solutions that have a low GDP content. Exposure to various dialysis solutions with a reduced GDP content has resulted in an increase in the effluent concentration of the mesothelial cell marker CA125, irrespective of the buffer used. Experimental studies in a long-term peritoneal exposure model in rats showed that the combination of a reduction in the concentration of lactate and replacement of lactate with pyruvate resulted in a reduction of the number of peritoneal blood vessels. Results of drug therapy have been studied in various animal models. Their use in patients is still experimental., Conclusions: Strategies to preserve the peritoneum aim at reducing membrane exposure to bioincompatible solutions. Currently available dialysis fluids that are more biocompatible are likely to have some beneficial effects. Further research on the development of dialysis solutions that use combinations of osmotic agents and alternative buffers is necessary.

Objective: Peritoneal dialysis (PD) with a 7.5% icodextrin-containing dialysis solution provides prolonged ultrafiltration compared with glucose-based dialysis solutions. Colloid osmosis is the most likely mechanism, but studies in rats suggest it is caused by an increase in osmolality due to degradation of icodextrin. Therefore, human spent dialysate was analyzed with high-performance liquid chromatography (HPLC) using gel permeation size-exclusion chromatography. An increasing peak (with a low molecular weight, < 1000 Da) was observed during the dwell. The aim of this study was to quantitate breakdown products of icodextrin (which could explain this peak) and investigate whether there was a relationship with dialysate amylase concentration and dialysate osmolality., Design: Long-dwell effluents (dwell time 9.15- 14.30 hours) obtained from 12 PD patients using a 7.5% icodextrin solution during the night were analyzed. The following icodextrin breakdown products were measured: maltotetraose (G4), maltotriose (G3), maltose (G2), and glucose (G1). In 6 of these patients, the sugars maltoheptaose (G7), maltohexaose (G6), and maltopentaose (G5) were also determined in both effluent and plasma. In addition, G4, G3, G2, and G1 were measured in four Wistar rats during a 6-hour dwell study., Results: In the human studies, the median distribution of the sugars in the effluent was G4,6.7%; G3,16.5%; G2, 23.1%; and G1, 53.5%. The osmolality in spent dialysate ranged between 288 and 326 mOsm/kg H2O. The median contribution of the sugars G2 - G4 was 5.4 mOsm/kg H2O. No correlation was present between dialysate osmolality and duration of the dwell (r= -0.04, p= 0.91); nor was there a relation between the concentration of G2 and duration of the dwell (r = 0.50, p = 0.10). No relationship was found between the amount of amylase and the concentration of G2 in the effluent (r = 0.49, p = 0.10), nor between the total concentration of the sugars G2 - G4 in the spent dialysate and dialysate osmolality (r = -0.31, p = 0.33). However, a strong correlation was seen between urea concentration and osmolality (r= 0.85, p < 0.001), and also between sodium concentration and dialysate osmolality in the spent dialysate (r = 0.92, p < 0.0001). The levels of the sugars G2, G3, and G4 in effluent were higher than in unused dialysate, but lower than or similar to plasma levels. Concentrations of the sugars G5, G6, and G7 were lower in spent dialysate than in unused dialysate, and higher than in plasma. In the rat study, dialysate osmolality increased with the duration of the dwell. A clear relationship was present between osmolality and concentration of the sugars G2 - G4 in the effluent. The median amount of amylase in the effluent was 1252 U/L., Conclusion: A 7.5% icodextrin-based dialysis solution used during the long exchange caused only a slight increase in dialysate osmolality in humans. The osmolality at the end of the dwell in the human situation was dependent mainly on concentrations of the small solutes urea and sodium in the effluent. The contribution of icodextrin degradation products was marginal. In the rat, however, a clear relationship was present between osmolality and icodextrin degradation products in spent dialysate, explaining the increased dialysate osmolality at the end of the dwell. The difference between the two species can be explained by the very high amylase concentrations in the rat, leading to a rapid degradation of icodextrin. The rat is therefore not suitable to study peritoneal fluid kinetics using icodextrin as an osmotic agent.