[Study of peritoneal water channel expression in rats]

Removal of excess fluid from patients with chronic renal failure is one of the major objectives of peritoneal dialysis (PD). Water movement from capillary to dialysate derives from the dialysate-to-capillary osmotic gradient across the peritoneum. To explain the mechanism of water movement driven by the osmotic gradient through the peritoneum, the notion of a water selective "ultra small pore" has been proposed. The purpose of this study was to investigate the involvement of peritoneal water channels in water movement across the peritoneum in PD. The abdominal cavity of male anesthetized rats was catheterized for administration of a series of artificial dialysates. Experimental PD was performed for 90-180 min with 25 ml of hyperosmotic dialysate generated by glucose (600 mOsm), sucrose (600 mOsm), and sodium (1800 mg/dl, 600 mOsm). Analysis of the sodium concentration and osmolality of dialysate during experimental PD showed mercurial sensitive water transport that was compatible with water channel-mediated water transport in the peritoneum. RT-PCR amplification with cDNAs constructed from peritoneal mRNA revealed the existence of both AQP1 (CHIP28) and AQP4 (MIWC) water channels in the peritoneum. PD with hyperosmotic dialysate did not affect the expression of peritoneal water channels. As a result of an in situ hybridization study to investigate the localization of the peritoneal water channels, it was found that both channels were expressed in the sub-mesothelial layer containing capillaries. The results obtained in this study suggest that peritoneal water channels might play a role in fluid removal during PD.