Abstract
Disturbance of peritoneal ultrafiltrative activity is frequently observed in patients on long-term standard CAPD, though peritoneal permeability itself is not greatly affected. The beneficial effect of phosphatidylcholine (PC) for ameliorating this disturbed ultrafiltration has been advocated. However, the exact mechanism underlying the effect of PC has not yet been determined. In this study we have investigated the effects of pH, as well as osmotic pressure, of dialysis fluid on cultured mesothelial cells. In addition, the effect of PC was evaluated. Mesothelial cells were cultured from stripped human omentum cells obtained by abdominal surgery and were radiolabelled with 51Cr. The medium was removed and the radiolabelled cells were exposed to dialysis fluids of various pH and osmotic pressure values. The damage to mesothelial cells induced by differences in dialysis fluids was evaluated by cytotoxic assay using 51Cr release into the medium. The protective effect of PC on cultured mesothelial cells was investigated by cytotoxic assay under 4 different conditions of purified PC in the media, at various concentrations of each. Low pH dialysis fluids showed lower cytotoxic activity than those of neutral or high pH, and cytotoxicity increased as the osmotic pressure of the dialysis fluid became higher. The inclusion of dipalmitoyl-phosphatidylcholine (DPPC) in dialysis fluid produced a suppressive effect on cytotoxicity, and a concentration of 50-100mg/l was found to be optimal for protecting the mesothelial cells. The concentration of phospholipid in the supernatant was relatively decreased when DPPC was added to the dialysis fluid. We presume that this effect was due to the altered state of the mesothelial cells. Thus, low pH and/or high osmotic pressure in the dialysis fluid have cytotoxic effects on mesothelial cells while dialysis fluid containing DPPC at 50-100mg/l appears to exert a protective effect on mesothelial cells.
