Peritoneal Dialysis In Rats Research Articles

3,4-DGE in Peritoneal Dialysis Fluids Cannot be Found in Plasma after Infusion into the Peritoneal Cavity

Glucose degradation products (GDPs) are important in the outcome of peritoneal dialysis (PD) treatment. 3,4-dideoxyglucosone-3-ene (3,4-DGE) is the most cytotoxic GDP found in conventionally manufactured fluids and may, in addition, be recruited from 3-deoxyglucosone (3-DG). It is not known what happens with those GDPs in patients during PD. The aim of this study was to investigate if the 3,4-DGE and 3-DG in PD fluids can be found in plasma during treatment. PD patients were dialyzed with a conventional PD fluid containing 43 micromol/L 3,4-DGE and 281 micromol/L 3-DG. Parallel experiments were performed in rats as well as in vitro with human plasma. The rats were dialyzed with a PD fluid containing 100 micromol/L 3,4-DGE and 200 micromol/L 3-DG. The concentration of 3,4-DGE in the peritoneum decreased at a much higher rate than 3-DG during the dwell. 3,4-DGE was not, however, detected in the plasma of patients or rats during dialysis. The concentration of 3-DG in plasma peaked shortly after infusion of the fluid to the peritoneal cavity. The concentration of 3,4-DGE during experimental incubation in plasma decreased rapidly, while the concentration of 3-DG decreased only 10% as rapidly or less. 3,4-DGE could not be detected in plasma from either PD patients or rats during dialysis. This is presumably due to its high reactivity. 3-DG may, on the other hand, pass through the membrane and be detected in the blood.

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.

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.

Pharmacokinetics of Fluconazole and Fosfluconazole after Intraperitoneal Administration to Peritoneal Dialysis Rats

Fluconazole (FLCZ) is an antifungal agent that is efficacious in the treatment of fungal peritonitis. Fosfluconazole (F-FLCZ) is the phosphate prodrug of FLCZ, which is highly soluble compared with FLCZ. F-FLCZ is useful against fungal peritonitis in continuous ambulatory peritoneal dialysis (CAPD) patients because it has a high water solubility. The aims of the present study were to characterize the peritoneal permeability of FLCZ and the pharmacokinetics of FLCZ and F-FLCZ after intraperitoneal (i.p.) administration to peritoneal dialysis rats. FLCZ or F-FLCZ was administered intravenously and intraperitoneally. After the i.p. administration of F-FLCZ, FLCZ was detected in circulating blood and the dialyzing fluid in peritoneal dialysis rats. The concentration of plasma FLCZ after the i.p. F-FLCZ administration was lower than that after the intravenous (i.v.) F-FLCZ administration. It is considered that the dose should be increased appropriately when F-FLCZ is administered intraperitoneally. The profiles of plasma FLCZ after i.v. and i.p. administrations were analyzed using a two-compartment model in which the distribution volume of the peripheral compartment was fixed at a volume of the dialyzing fluid (peritoneal dialysis PK model). The peritoneal dialysis PK model could describe the profiles of plasma and dialyzing fluid FLCZ. These results suggest that FLCZ and F-FLCZ could be administered intraperitoneally for the treatment of fungal peritonitis in CAPD patients.

Acute Peritoneal Dialysis in Rats Results in a Marked Reduction of Interstitial Colloid Osmotic Pressure

The aim of this study was to investigate whether the interstitial colloid osmotic pressure (COP(i)) of peritoneum is of importance for peritoneal fluid reabsorption during peritoneal dialysis (PD). For testing this hypothesis, a method to isolate interstitial fluid from the peritoneal membrane and to measure the interstitial COP(i) in the normal peritoneum and directly after the initiation of PD needed to be developed and validated. Eighteen female rats were anesthetized subcutaneously in the neck region with fentanyl-midazolam (1:1). Nylon wicks were implanted postmortem by means of a plastic catheter in the tissue just underneath the peritoneal surface. The characteristics of this fluid were compared with that isolated from wicks that were implanted in intermuscular spaces in hindlimb muscle and back subcutis. All wicks were removed after 20 min and centrifuged. The wick fluid was collected and analyzed in a colloid osmometer constructed for submicroliter samples, and interstitial fluid COP was compared with that of plasma. PD was initiated by injecting 20 ml of 3.86% glucose-containing PD fluid (Dianeal) into the peritoneal cavity, over a dwell time of 4 h. Control rats received no PD. The ratio of COP(i) to that of plasma (COP(p)) during control was 0.65 +/- 0.05 in peritoneum, 0.53 +/- 0.04 in muscle, and 0.59 +/- 0.05 in skin. After a PD dwell, the ratio was 0.29 +/- 0.03 in peritoneum, 0.54 +/- 0.08 in muscle, and 0.41 +/- 0.06 in skin. Thus, the COP ratio in peritoneum fell by 55% (P = 0.014) and in skin by 30% (P = 0.03), whereas the COP ratio in muscle was unchanged. The results suggest that acute PD results in a marked fall of the COP(i) in the peritoneal membrane, shifting the Starling equilibrium toward an absorptive state. The effect was restricted to the peritoneal membrane and, to some extent, the skin. It is speculated that the increase in peritoneal hydrostatic pressure after PD causes an increase in interstitial tissue volume, with primarily a dilution of interstitial colloids.

Activation of matrix metalloproteinase-2 causes peritoneal injury during peritoneal dialysis in rats.

Sclerosing peritonitis (SP) and encapsulating peritoneal sclerosis (EPS) are serious complications of continuous ambulatory peritoneal dialysis. Although we have shown previously that matrix metalloproteinase-2 (MMP-2) is increased in peritoneal injury leading to SP/EPS, most of the MMP-2 in the dialysate drained from the peritoneal cavity was the latent form that was lacking activity. In the present study, we investigated whether MMP-2 causes peritoneal injury. To create an animal model of peritoneal injury, we administered intraperitoneally chlorhexidine gluconate to rats. Dialysate drained from these rats was analysed by gelatin zymography and MMP-2 activity was analysed by an in situ film zymography method. In vitro myofibroblasts were cultured in collagen three-dimensional culture and then MMP-2 in conditioned medium from the culture was analysed by gelatin zymography. Zymographic analysis revealed that latent form MMP-2 levels were high in the dialysate from peritoneal injury rats, whereas the active form was barely detectable. MMP-2 activity in the peritoneal tissue of the peritoneal injury rats was strongly detected by in situ film zymography. In vitro myofibroblasts were promoted to produce MMP-2 and to activate MMP-2 in collagen three-dimensional culture. In the present model, most of the MMP-2 was in the latent form, but activation of MMP-2 was promoted in the peritoneum during peritoneal injury. Activated MMP-2 may be associated with the progression of peritoneal injury.

N-Acetylglucosamine – An Osmotic Solute for Peritoneal Dialysis without Inducing Hyperinsulinemia

Methods: N-Acetylglucosamine (NAG) was compared to glucose as an osmotic solute during peritoneal dialysis in rats. The effect of the tested solutes on blood glucose and insulin levels during dialysis was evaluated. Results: During 6-hour exchange with NAG (220 mmol/l) solution, the dialysate volume was higher than in rats dialyzed with fluid containing glucose (220 mmol/l; GLU: 34.5 ± 1.7 vs. 32.8 ± 1.1 ml, respectively; p < 0.05). The peritoneal permeability to protein (D/S × 1,000) was lower in the NAG group (9.7 ± 2.5 vs. 16.3 ± 5.6 in GLU; p < 0.02). Dialysis with GLU-based solution resulted in hyperglycemia up to 180 ± 39 mg/dl; in the NAG group the increase in the blood glucose level was moderate (up to 91 ± 9 mg/dl; p < 0.001). Dialysis with GLU fluid caused an increase in blood insulin level by 53.2 ± 62.4 pmol/l, whereas the insulin blood concentration in NAG-treated animals was increased by 5.0 ± 5.4 pmol/l (p < 0.001). Conclusions: NAG is more effective than GLU osmotic solute during peritoneal dialysis and it reduces peritoneal permeability to protein. Dialysis with NAG results in lower hyperglycemia and hyperinsulinemia, both effects are favorable in diabetic peritoneal dialysis patients.

Blood flow limitation in vivo of small solute transfer during peritoneal dialysis in rats.

The aim of this study was to determine whether or to what extent transperitoneal flux of small solutes is reduced at low blood flows during peritoneal dialysis (PD) in rats. Peritoneal blood flow reductions were achieved by bleeding anesthetized (300 g) rats by 25% of their blood volume. After bleeding, a 2 h PD dwell was started using standard PD fluid. The permeability-surface area product (PS) for (51)Cr-EDTA and glucose were assessed, as well as the transperitoneal clearance (Cl) of albumin. Control animals were not bled. After bleeding, peritoneal blood flow declined from 145 +/- 17 perfusion units (PU) to 59 +/- 12 PU (P = 0.001). Concomitant with this reduction, PS for (51)Cr-EDTA fell from 0.284 +/- 0.01 ml/min to 0.216 +/- 0.01 ml/min (P = 0.006) and PS for glucose from 0.338 +/- 0.02 ml/min to 0.294 +/- 0.01 ml/min (P = 0.046). Mean arterial BP (MAP) dropped from 133 +/- 4 mmHg to 61 +/- 5 mmHg (P = 0.008). Cl of albumin fell largely in proportion to the estimated capillary hydrostatic pressure drop, i.e., from 6.1 +/- 0.7 microl/min to 2.3 +/- 0.3 microl/min (P = 0.001). The results demonstrate that the transperitoneal clearances of small solutes are blood flow limited during PD, when peritoneal perfusion is markedly reduced. The level of flow limitation was, however, much lower than expected and observed in other tissues. Albumin transport, which is not blood flow limited, was reduced largely in proportion to the calculated capillary hydrostatic pressure decrease.

Replacement of Glucose with N-Acetylglucosamine in Peritoneal Dialysis Fluid—Experimental Study in Rats

Glucose is still used as an osmotic solute in peritoneal dialysis fluids, despite evidence of its local (peritoneal) and systemic toxicities. However a constant search is underway for a new, more biocompatible osmotic solute for peritoneal dialysis fluids. The present study evaluated N-acetylglucosamine (NAG) in a concentration of 220 mmol/L as an alternative to glucose for the osmotic solute in peritoneal dialysis fluid, during chronic peritoneal dialysis in rats. For 8 weeks, male Wistar rats were infused with glucose-based or NAG-based dialysis fluid. Intraperitoneal inflammation and peritoneal permeability and morphology were evaluated in all rats during the study. Repeated intraperitoneal infusion of the NAG-based dialysis fluid resulted in a weaker intra-abdominal inflammatory reaction as compared with the reaction in rats infused with glucose-based dialysis solution. At the end of the study, the concentration of hyaluronan in the peritoneal interstitium obtained from NAG-treated rats was higher than that found in the interstitium taken from animals exposed to dialysis fluid containing glucose. Also, peritoneal permeability to total protein was lower in NAG-treated rats. As an alternative to glucose, NAG used for the osmotic solute in peritoneal dialysis solution decreases the intraperitoneal inflammatory reaction induced by the process of peritoneal dialysis and, indirectly (owing to the increased hyaluronan content in the peritoneal interstitium), diminishes peritoneal permeability to protein.

The Effect of Icodextrin-Based Solutions on Peritoneal Transport in Rats Undergoing Chronic Peritoneal Dialysis

We evaluated the effect of icodextrin on peritoneal permeability and inflammation in an experimental chronic peritoneal dialysis (PD) model with repeated dwell studies (DSs) in non uremic rats. Male Wistar rats with implanted peritoneal catheters were infused twice daily for 3 weeks with 20 mL Dianeal 3.86% (Baxter Healthcare Corporation, Deerfield, IL, U.S.A.) (n = 11) or icodextrin 7.5% (n = 12). After 10 days (DS1) and 21 days (DS2), a 4-hour DS using 30 mL icodextrin solution was performed in conscious animals. Radioiodinated serum albumin (RISA) was used as a macromolecular volume marker. Blood samples were drawn before the start of the dwell and at its end. We observed a steady increase in intraperitoneal volume (IPV) versus dwell time (0-240 minutes) during DS1 and DS2 in both groups. No significant differences in peritoneal permeability to solutes were observed between the groups. However, in both groups, IPV volume was significantly higher during DS2 after the 4-hour dwell time [IPV icodextrin: 34.4 +/- 1.4 mL (DS1), 35.4 +/- 1.1 mL (DS2), p < 0.002; IPV Dianeal: 34.2 +/- 0.9 mL (DS1), 35.2 +/- 0.7 mL (DS2), p < 0.01]. Changes of peritoneal permeability seen during in vivo experimental models of chronic peritoneal dialysis in rats with repeated dwell studies are comparable to results obtained in humans on continuous ambulatory peritoneal dialysis (CAPD).

New Animal Models for Encapsulating Peritoneal Sclerosis—Role of Acidic Solution

Encapsulating peritoneal sclerosis (EPS), in which all or part of the intestine is enveloped in a fibrous ball resembling a cocoon, is a serious complication of peritoneal dialysis (PD). The aim of the present study was to investigate whether pH-neutral or acidic dialysis solutions induce peritoneal fibrosis. We divided 18 male Wistar-Kyoto (WKY) rats into three groups and dialyzed them with various solutions as follows: group I, 10 mL acidic dialysis solution (pH 3.8, containing 1.35% glucose), n = 6; group II, 10 mL pH 5.0 dialysis solution, n = 6; and group III, 10 mL neutral dialysis solution (pH 7.0), n = 6. Peritoneal catheters were inserted, and dialysis solution was injected every day for 40 days. At the end of the experiment, a peritoneal equilibration test (PET) was performed. Expression of mRNA of aquaporins 1 and 4 (AQP-1 and AQP-4) in the peritoneum were studied by semiquantitative reverse-transcriptase polymerase chain reaction (RT-PCR). In rats treated with pH 3.8 dialysis solution, necropsy findings revealed features identical to those of EPS. The typical appearance was of granulation tissue or fibrotic tissue (or both) covering multiple surfaces. Multiple adhesions were present. In microscopic examinations, peritoneal fibrosis and loss of mesothelium were found. In rats treated with pH 7.0 dialysis solution, no signs of EPS were seen. In rats treated with pH 5.0 dialysis solution, milder changes (subserosal thickening and partial adhesion of the peritonea) were observed. The mRNA of AQP-1 and AQP-4 were expressed in the peritonea of the rats. The expression of the AQPs was significantly suppressed in rats treated with pH 3.8 dialysis solution. In rats, long-term intraperitoneal injection of acidic dialysis solution produced features typical of EPS in humans. Newly developed neutral dialysis solutions protected the against the development of EPS during peritoneal dialysis in rats.

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.

Peritoneal Transport of Glucose in Rat

To evaluate the convective transport characteristics of glucose and the effect of high glucose and insulin during experimental peritoneal dialysis in rat. Male Sprague-Dawley rats weighing 300-400 g were used in this study. Mannitol (5%) was used as osmotic agent. Glucose was added to dialysis solution to yield a concentration of 100 mg/dL (group 1) or 300 mg/dL (group 2). Mannitol solution (5%) containing the same concentration of electrolytes and lactate but without glucose was used as control (group 3). In group 2, blood sugar was maintained at approximately 300 mg/dL by continuous intravenous infusion of 25% glucose solution and 0.9% NaCl solution. A 2-hour dwell study was performed with 30 mL of test solutions. Intraperitoneal volume was calculated by volume marker (18.5 kBq of 131I-human radioiodinated serum albumin, RISA) dilution with corrections made for the elimination of RISA from the peritoneal cavity (K(E)) and sample volume. The diffusive mass transport coefficient (K(BD)) and sieving coefficient (S(BRF)) were calculated by using the Babb-Randerson-Farrell model. S was also calculated directly by using isocratic methods (S(I)). The peritoneal fluid absorption rate (K(E)) was taken into account for the calculation of S(I). Intraperitoneal volume was significantly higher in group 2 compared with groups 1 and 3. Peritoneal fluid absorption rate, K(E), was similar in all three groups. S(BRF) and S(I) for glucose were significantly lower in group 2 compared with groups 1 and 3. S(BRF) for glucose in group 2 was below zero and S(I) near zero. K(BD) for glucose was significantly higher in group 2 than in groups 1 and 3. Plasma and dialysate concentrations of insulin increased during the initial hour and then decreased to the baseline value in groups 1 and 3, while in group 2 it continuously increased. Significantly lower sieving coefficients for glucose in the high glucose and high insulin group suggest that transport mechanisms other than simple passive transport are involved in peritoneal glucose transport, and that high glucose per se and/or high insulin may be important factors that determine glucose transport characteristics.

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.

The Effects of Ouabain and Potassium on Peritoneal Fluid and Solute Transport Characteristics

We reported anomalous transport characteristics of potassium during experimental peritoneal dialysis in rats and suggested that mechanisms of peritoneal potassium transport could be other than simple passive transport. Intracellular transport of potassium in cultured human mesothelial cells was reported to be regulated by three different pathways, such as channels blocked by ouabain, channels blocked by furosemide, and other. To investigate the effect of ouabain on peritoneal potassium and water transport characteristics. A single 4-hour peritoneal dwell was performed in 28 Sprague-Dawley rats. To minimize the diffusive transport of potassium, 4.5 mmol/L of KCl was added into conventional dialysis solution with 3.86% glucose [acidic peritoneal dialysis solution (APD)]. To evaluate the effect of the pH of dialysis solution on the transport of potassium and water, 4 mmol/L of NaOH was added into the potassium-containing study solutions [neutral peritoneal dialysis solution (NPD)]. To evaluate the effect of a potassium channel blocker on peritoneal potassium transport ATPase sensitive Na+-K+-transport inhibitor, ouabain (10(-5) mmol/L) was added to dialysis solutions immediately before the dwell study in eight rats with APD (APD-O) and six rats with NPD (NPD-O). Ouabain was not added in eight and six rats with APD and NPD (APD-C and NPD-C, respectively). They were used as control. Infusion volume was 30 mL. The intraperitoneal volume (V(D)) was estimated by using a volume marker dilution method with corrections for the elimination of volume marker, radioiodinated human serum albumin (RISA), from the peritoneal cavity (K(E)). The diffusive mass transport coefficient (K(BD)) and sieving coefficient (S) were estimated using the modified Babb-Randerson-Farrell model. V(D) was significantly higher (p < 0.05 from 90 min to 240 min) and K(E) (0.027+/-0.018 mL/min for APD-O, 0.026+/-0.017 mL/min for NPD-O, and 0.030+/-0.022 mL/min for NPD-C, vs 0.058+/-0.030 mL/min for APD-C, p < 0.05 for each) significantly lower during dialysis with APD-O, NPD-O, and NPD-C than with APD-C. The intraperitoneal glucose expressed as a percentage of the initial amount was significantly higher with APD-O, NPD-C, and NPD-O than with APD-C (p < 0.05 from 90 min to 240 min). K(BD) for sodium was higher during dialysis with ouabain than without ouabain, while K(BD) for urea, glucose, and potassium, and S for urea, glucose, sodium, and potassium did not differ between the four groups. The physiologic potassium concentration in neutral dialysis solutions and the use of ouabain decreased the intraperitoneal fluid absorption. The diffusive transport coefficient and sieving coefficient for potassium did not differ, while the diffusive transport coefficient for sodium increased during use of ouabain.

N-Acetylglucosamine Changes Permeability of Peritoneum during Chronic Peritoneal Dialysis in Rats

To evaluate the effect of supplementation of dialysis fluid with N-acetylglucosamine (NAG) on the permeability of peritoneum during chronic peritoneal dialysis in rats. Experiments were performed on rats with surgically implanted peritoneal catheters. Dialysis solution [Dianeal 1.5% (Baxter, Deerfield, IL, U.S.A.) supplemented with either NAG 50 mmol/L or glucose 50 mmol/L (control)] was infused intraperitoneally twice, every day, for 8 weeks. Peritoneal equilibration tests (PET) were performed in all animals at the beginning of the study and after 8 weeks of dialysis. Additionally, at the end of each week, dialysis solution infused in the morning was drained after 4 hours of intraperitoneal dwell. White blood cell count, creatinine, and total protein concentrations were measured in the effluent dialysate. After 8 weeks of dialysis, the morphology of the peritoneum was studied. In rats exposed to dialysis fluid supplemented with NAG, peritoneal permeability to creatinine and proteins was reduced when compared to animals dialyzed with glucose solution. In NAG treated animals, staining with alcian blue for polyanions in the peritoneal interstitium was significantly stronger than in rats dialyzed with glucose solution. Chronic peritoneal dialysis with dialysis solution supplemented with N-acetylglucosamine causes accumulation of glycosaminoglycans in the peritoneal interstitium, which results in a change of peritoneal permeability.

Peritoneal Surface Area and Its Permeability in Rats

Evaluation of peritoneal surface area and its permeability during dialysis in rats of various ages. Study I: planimetry of peritoneum and its topographic areas was performed in 47 rats of various ages (8-30 weeks). Study II: net ultrafiltration (UF), dialysate-to-serum ratios for urea, creatinine, albumin, and total protein as well as their peritoneal permeability coefficients, were measured during a 1-hour peritoneal exchange with Dianeal 2.5%, in 21 rats of different ages (9-30 weeks) and with various peritoneal surface areas. Male Wistar rats. The peritoneal surface area in rats increases during aging, but young animals with lower body weight have a relatively larger peritoneal surface area than older, larger animals. The area of the topographic fragments of peritoneum expressed as a percentage of the total peritoneal surface is steady during aging. Efficiency of transperitoneal water removal expressed as net UF per amount of absorbed glucose declines in older animals, with larger peritoneal surface areas. Dialysate/serum ratio of solutes transported from blood to dialysate is proportional to peritoneal surface area. Permeability coefficient (K) of peritoneum to urea and creatinine is unchanged during the aging of animals. However peritoneal permeability (K) to albumin increases during aging, with the opposite tendency for total proteins. Kinetics of peritoneal dialysis in rats of different ages is determined by peritoneal surface area and permeability of peritoneum to individual solutes.

In vivo inhibition of transcellular water channels (aquaporin-1) during acute peritoneal dialysis in rats.

During peritoneal dialysis (PD), a major portion of the osmotically induced water transport to the peritoneum can be predicted to occur through endothelial water-selective channels. Aquaporin-1 (AQP-1) has recently been recognized as the molecular correlate to such channels. Aquaporins can be inhibited by mercurials. In the present study, HgCl2 was applied locally to the peritoneal cavity in rats after short-term tissue fixation, used to protect the tissues from HgCl2 damage. Dianeal (3.86%) was employed as dialysis fluid, 125I-albumin as an intraperitoneal volume marker, and 51Cr-EDTA (constantly infused intravenously) to assess peritoneal small-solute permeability characteristics. Immunocytochemistry and immunoelectron microscopy revealed abundant AQP-1 labeling in capillary endothelium in peritoneal tissues, representing sites for HgCl2 inhibition of water transport. HgCl2 treatment reduced water flow and inhibited the sieving of Na+ without causing any untoward changes in microvascular permeability, compared with that of fixed control rats, in which the peritoneal cavity was exposed to tissue fixation alone. In fixed control rats, the mean intraperitoneal volume (IPV) increased from 20.5 +/- 0.15 to 25.0 +/- 0.52 ml in 60 min, whereas in the HgCl2-treated rats, the increment was only from 20.7 +/- 0.23 to 23.5 +/- 0.4 ml. In fixed control rats, the dialysate Na+ fell from 135.3 +/- 0.97 to 131.3 +/- 1.72 mM, whereas in the HgCl2-treated rats the dialysate Na+ concentration remained unchanged between 0 and 40 min, further supporting that water channels had been blocked. Computer simulations of peritoneal transport were compatible with a 66% inhibition of water flow through aquaporins. The observed HgCl2 inhibition of transcellular water channels strongly indicates a critical role of aquaporins in PD and provides evidence that water channels are crucial in transendothelial water transport when driven by crystalloid osmosis.

Role of Diaphragmatic, Visceral, and Parietal Pathways in Peritoneal Fluid Absorption in Rat Peritoneal Dialysis

Assessment was made of the contribution of lymphatic and non lymphatic fluid absorption to net fluid loss from the peritoneal cavity. Diaphragmatic, visceral, and parietal pathways in lymphatics and nonlymphatics were examined using a rat model with adhesion of the diaphragm to the liver, evisceration, these two procedures in combination, and without treatment. In each of these cases, six rats were used, each dialyzed for 180 min with Krebs–Ringer solution. The peritoneal net fluid absorption rate (PNFAR) was determined based on the disappearance of 1251-bovine serum albumin (BSA) from the peritoneal cavity and the lymphatic absorption rate (LAR), was based on the appearance of this albumin in the blood. Seventy-eight percent of net fluid loss occurred via the non lymphatic pathway, primarily through parietal and visceral absorption, and the remaining 22% through the lymphatics, the main pathway being the subdiaphragmatic lymphatics. Nonlymphatic fluid absorption would thus appear to be a major route of fluid loss from the peritoneal cavity in rat peritoneal dialysis.