Acute inflammation in peritoneal dialysis: experimental studies in rats. Characterization of regulatory mechanisms.

The predominant problems associated with peritoneal dialysis (PD) are ultrafiltration failure and peritonitis. PD maintains a state of intraperitoneal inflammation that affects the structure and function of the peritoneal membrane, potentially impairing ultrafiltration efficiency. Paradoxically, some PD fluids also have anti-inflammatory properties that may compromise the immune defense against peritonitis. This anti-inflammatory feature is mostly due to the glucose degradation products (GDPs), formed during heat-sterilization and storage of PD fluids. The main purpose of the present thesis was to study regulatory mechanisms behind the acute intraperitoneal inflammatory response in PD in the presence and absence of experimental peritonitis. Rats were exposed to a single dose of heat- or filter sterilized PD fluids either as an i.p. injection or as an infusion through an indwelling catheter, with or without supplementations, or pretreatment of the animals. The dwell fluid was analyzed zero, two and four hours later concerning activation of the complement and coagulation cascades, neutrophil recruitment and respiratory burst, ultrafiltration volumes, cytokine-induced neutrophil chemoattractant (CINC-1), rat mast cell protease 2 (RMCP-2), glucose, urea and histamine concentrations and ex vivo/in vitro intraperitoneal chemotactic activity. Exposure to filter sterilized PD fluid alone induced intraperitoneal complement activation and coagulation, neutrophil recruitment and increased the levels of CINC-1 during the dwell. Intraperitoneal concentrations of the mast cell markers histamine and RMCP-2 changed little during the dwells and did not indicate mast cell activation. Low molecular weight heparin (LMWH) and C5 blockade improved ultrafiltration. Pretreatment with cobra venom factor, known decomplementing agent, blocked the CINC-1 release and the neutrophil recruitment and improved ultrafiltration. In combination with experimental peritonitis, heat sterilized PD fluid compared to filter sterilized, inhibited the CINC-1 release and the recruitment of neutrophils to the peritoneal cavity without affecting the intraperitoneal complement activation. The results of the present thesis indicate that addition of LMWH to the PD fluid improves ultrafiltration, probably by blocking C5a activity. C5 blockade seems to improve ultrafiltration by a mechanism that involves a reduction in glucose transport, possibly by reducing C5 induced vasodilatation. Complement activation is an early step in the acute reaction to PD and probably mediates the downstream events that lead to the recruitment of inflammatory cells to the peritoneal cavity. The cells involved in the release of CINC-1 later in this sequence are probably the mesothelial cells. During experimental peritonitis, heat sterilized PD fluids inhibited the neutrophil respiratory burst response of intraperitoneal neutrophils. Heat sterilized PD fluids also inhibit the recruitment of neutrophils to the peritoneal cavity by a mechanism independent of complement activation but probably depending on cytokine CINC-1 release during peritonitis.