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Peritoneal fibrosis (PF) is one of the most serious causes of technique failure in long-term peritoneal dialysis (PD). Although the mechanisms responsible for the genesis of PF are not well understood, angiotensin II is known to promote fibrosis and inflammation in various tissues and angiotensin converting enzyme inhibitors (ACEIs) have been shown to attenuate those effects. We previously showed that ACEIs have beneficial effects on peritoneal alterations induced by hypertonic (3.86% glucose) PD solutions. In the present study, we investigated the local effects of intraperitoneal (IP) enalapril on peritoneal alterations induced by 3.86% glucose PD solution in rats on chronic PD. One week after peritoneal catheter insertion, 23 non uremic male rats were randomly divided into two groups: group A (n = 11) received 20 mL 3.86% PD solution twice daily, and group B (n = 12) received 20 mL 3.86% PD solution containing 1 mg/L enalapril twice daily. After 4 weeks of such infusions, we measured net ultrafiltration (UF) volume and obtained samples of visceral peritoneum from the liver for thickness measurement. Net UF was significantly higher (6.6 +/- 0.2 mL vs. 5.6 +/- 0.2 mL) and peritoneal thickness was significantly lower (30 +/- 5 microm vs. 52 +/- 0.8 microm) in group B. We conclude that intraperitoneal enalapril (an ACEI) protects the peritoneal membrane from the effects of hypertonic glucose. This protection might be mediated by enalapril's interference with angiotensin though inhibition of cytokine overexpression.

Peritoneal dialysis affects both the quantity and quality of connective tissue in the visceral peritoneum. In the present study, we report the alterations observed in the morphology of the superficial liver lobuli of dialyzed rats. The studies were performed in male Wistar rats weighing 250-350 g. Rats were exposed intraperitoneally to 0.9% NaCl, phosphate-buffered saline (PBS), or commercial dialysis solutions containing 3.86% glucose (Dianeal 3.86%: Baxter Healthcare SA, Castlebar, Ireland; CAPD3 and CAPD3-Balance: Fresenius Medical Care, Bad Homburg, Germany) twice daily for 4-6 weeks. At the end of the study, samples of the liver were taken and stained for light microscopy (hematoxylin and eosin, van Gieson). The results obtained in dialyzed rats were compared with those from the control, non dialyzed animals. In control animals, the surface of the hepatic parenchyma was smooth. In all dialyzed rats, irrespective of the solution used, folding of the surface of the liver parenchyma was found owing to penetration of connective tissue elements between the hepatocytes. In effect, folds of hepatocytes within the liver capsule became detached and isolated from the remaining cells of the lobules. The distinctive feature of that pathologic change was that its severity increased with the thickness of the peritoneum. The change was seen in rats exposed to any of the experimental solutions, and therefore appeared to be attributable to a non-specific reaction caused by exposure of the peritoneum to dialysis fluid and not to specific components of the fluid. The observed alterations in morphology seem to suggest disturbed function within the affected lobules. Further studies are necessary to confirm this hypothesis.

In previous studies, we showed that glucose reduces the morphologic changes in rat peritoneum caused by chronic intraperitoneal administration of 0.9% NaCl solution. In the present study, we set out to determine if the observed results were attributable to hyperosmolarity or to the metabolic effect of the glucose. Intraperitoneal catheters were implanted in 19 rats. The animals were then intraperitoneally exposed twice daily for 30 days to 20 mL 0.9% saline supplemented with either 250 mmol/L glucose (GLU, n = 9) or 250 mmol/L mannitol (MAN, n = 10). Control rats did not undergo catheter implantation or the dialysis procedure (CON, n = 6). At the end of the study, a 1-hour peritoneal equilibration test (PET) using Dianeal 3.86% (Baxter Healthcare SA, Castlebar, Ireland) was performed in every dialyzed rat to analyze peritoneal transport. Afterward, the rats were humanely killed by bleeding, and a semi-quantitative scale was used to evaluate adhesions in the peritoneal cavity. Imprints of the visceral mesothelium and samples of the visceral peritoneum (liver) were then taken and analyzed by light microscopy. The PET results for glucose, urea, creatinine, and total protein were comparable in both experimental groups. We found that intraperitoneal adhesions were more severe in the MAN group (6 rats with adhesions graded3) than in the GLU group (only 1 such rat). No difference in peritoneal thickness was observed between the experimental groups (MAN: 54.9 +/- 17.8 microns; GLU: 51.2 +/- 14.5 microns); however, in both experimental groups, the thickness was greater than in the CON group (3.9 +/- 0.6 microns). The density of the peritoneal blood vessels tended to be greater in the MAN group than in the GLU group (0.158 +/- 0.072 vessels/1000 microns 2 vs. 0.085 +/- 0.067 vessels/1000 microns 2, p = 0.0541). No visible blood vessels were evident in the CON group. The density of mesothelial cells was higher in the MAN group than in the GLU group (2456 +/- 333 cells/mm 2 vs. 2090 +/- 322 cells/mm 2, p0.05), and, in both experimental groups, the cell density was higher than in the CON group (817 +/- 100 cells/mm 2, p0.01). The nucleus: cytoplasm area ratio in mesothelial cells was comparable in the MAN and GLU groups (0.206 +/- 0.039 and 0.176 +/- 0.045), but that ratio was higher in both experimental groups than in the CON group (0.086 +/- 0.010, p0.01). We conclude that glucose-induced changes in the peritoneum of rats exposed to chronic peritoneal dialysis depend on both osmotic and metabolic effects.

In the past, we had observed that infusion of normal saline into the peritoneal cavity stimulates an inflammatory response. In the present study, we examined what effect the addition of glucose to normal saline would have on the peritoneal inflammatory response and change in peritoneal morphology. After catheter implantation, rats were infused intraperitoneally (i.p.) for 3 days with Dianeal 1.36% (Baxter Healthcare Corporation, Deerfield, IL, U.S.A.). Dialysate samples were collected on day 3 after a 4-hour dwell. Next, rats were exposed to either NaCl (n = 7) or NaCl with glucose 250 mmol/L (Glu, n = 7) twice daily for 4 weeks. After 2 weeks and 4 weeks of the study, dialysate samples were collected after a 4-hour dwell to analyze the activity of inflammatory reaction. At the end of the experiment, imprints of peritoneal mesothelium were taken. Control animals (C, n = 6) did not undergo catheter implantation or the dialysis procedure. The inflammatory reaction--cell count, cell differentiation, nitric oxide production, protein loss, and monocyte chemoattractant protein-1 (MCP-1) concentration in dialysate expressed as a percentage of the initial value--did not change during the study in rats exposed to NaCl. On the other hand, in Glu-treated animals, the protein concentration was decreased after 4 weeks of the study (74% +/- 23%, p0.05), as was MCP-1 (24% +/- 12%, p0.05). The nitrites concentration was decreased after 2 weeks (72% +/- 19%; p0.05). Intraperitoneal adhesions were found in 6 rats of the NaCl group (86%) and in only 4 rats (57%) of Glu group. In the NaCl rats, a higher density of mesothelial cells was observed (2792 +/- 510 cells/mm2) as compared with Glu rats (2028 +/- 561 cells/mm2; p0.05) and with control rats (1629 +/- 422 cells/mm2, p0.05). The NaCl group also showed a higher nucleus: cytoplasm surface ratio (0.25 +/- 0.03) as compared with the Glu group (0.18 +/- 0.02, p0.01) and with the control group (0.14 +/- 0.01, p0.01). Addition of glucose to normal saline suppresses the peritoneal inflammatory response and mesothelial hyperplasia occurring with intraperitoneal infusion of NaCl solution alone.