No Relation Between Peritoneal Fibrosis and Free Water Transport in a Rat Model

Free water transport (FWT) during peritoneal dialysis (PD) can easily be measured by Na+ kinetics. In long-term PD, FWT might reflect peritoneal fibrosis, but morphologic or functional relationships have not been investigated. Nonconventional dialysis solutions might be associated with better preservation of peritoneal tissues and function. We developed a long-term peritoneal exposure model in rats with impaired kidney function and investigated peritoneal morphology and function in that model after exposure to conventional and nonconventional solutions.Two studies were reanalyzed. Transport was assessed using a standard peritoneal permeability analysis adapted for the rat. Omental tissue was stained with picro-sirius red (PSR) for uniform quantification of fibrosis. A semiquantitative fibrosis score was also calculated.Rats (n = 9) exposed to a conventional solution for 16 weeks were compared with rats (n = 9) exposed to other solutions. Peritoneal transport parameters were similar, but the degree of fibrosis tended to be more severe in the conventional-solution group. Compared with the situation in humans, the contribution of FWT to ultrafiltration in rats was larger than that of small-pore fluid transport. No correlation between the percentage PSR positivity and FWT was observed. A marked difference in PSR positivity was found between the two studies.The long-term exposure model is not suitable for the study of relationships between FWT and peritoneal fibrosis. Quantitative assessment of the fibrosis is difficult