Morphological changes of the peritoneum in peritoneal dialysis patients

Background Long-term peritoneal dialysis (PD) requires that the peritoneal membrane remain effective for dialysis. Research directed toward human peritoneal morphology and structure is limited. The present study was performed to investigate morphological changes of the human peritoneal membrane during PD and to elucidate the possible mechanisms of its functional deterioration. Methods A total of 32 peritoneal biopsies were performed in normal subjects (n=10),uremic nondialysis patients (n=12) at the time of catheter insertion,and PD patients (n=10) at the time of catheter removal or reinsertion or at the time of renal transplantation. Peritoneal morphology was examined by light microscopy,scanning electron microscopy,and transmission electron microscopy. Results The peritoneal membrane in normal subjects consisted of a monolayer of mesothelial cells on a basement membrane and a layer of connective tissue containing cells,blood vessels,and lymphatic vessels. Mesothelial cells were polygonal,often elongated,and had numerous microvilli on their luminal surface. There were lots of oval or roundish pinocytotic vesicles in the cytoplasm of the mesothelial cells. The peritoneal morphology of uremic nondialysis patients was similar to that of normal subjects. However,significant abnormalities of the peritoneal membrane were observed in PD patients,and the changes were found to be progressive. Microvilli were the first site of damage which involved microvilli shortening,a gradual reduction in their number,and,eventually,the total disappearance of microvilli. Mesothelial cells then detached from the basement membrane, disappearing completely in some cases. In the end,the peritoneal membrane consisted only of submesothelial connective tissue without any cells.Conclusions PD can modify peritoneal morphology and structure. The morphological change is progressive and may be one of the important causes of peritoneal failure. Peritoneal biopsies can provide lots of valuable information about the effects of PD. Studying the relationship between peritoneal structure and its function proved very useful for understanding the physiopathology of the peritoneum during PD.

Expression of aquaporin-1 in the human peritoneum and the effect of peritoneal dialysis on its expression

Objective To investigate the expression of aquaporin-1 (AQP1) in the human peritoneum and to evaluate the effect of peritoneal dialysis (PD) on its expression.Methods Peritoneal biopsies were obtained from normal subjects (n =10), uremic nondialysis patients (n = 12) at catheter insertion and PD patients ( n = 10) at the time of catheter removal, reinsertion or renal transplantation. Western blot, immuno-histochemical staining and reverse transcript-polymerase chain reaction ( RT-PCR) techniques were used to investigate AQP1 expression.Results All peritoneal samples expressed AQP1 at both mRNA and protein levels. Western blot revealed a major band at 28 kD as well as more diffuse bands between 35 and 50 kD. The 28 kD band represents the nonglycosylated form of the protein while the 35 - 50 kD bands correspond to glycosylated AQP1. Immunohistochemical staining found the positive deposits were distributed in the mesothelial cells, endothelial cells of capillaries, venules and small veins, whereas no signal was detected in the arterioles. Semi-quantitative analysis showed that AQP1 expression was remarkably stable in all samples, whatever their origin (P>0. 05).Conclusions Our findings suggested that AQP1 is the molecular counterpart of an ultra small pore during PD. Secondly, the peritoneal mesothelial cell might also be involved in peritoneal transcellular water transport. As regards whether or not the structural or distributional alterations of AQP1 in the peritoneum may be more obviously expressed during PD, further study is needed.