Altered Expression of Peritoneal Aquaporin-1 and Water Transport during Long-term Peritoneal Dialysis in Rats

Lee, Won Jae; Lee, Jun Yeop; Tak, Woo Taek; Kim, Ki Kwon; Kwon, Tae Hwan; Kim, Eung Suk; Lee, Jeong Ho

Abstract

BACKGROUND
The present work was designed to examine the altered expression of peritoneal AQP-1 and water transport of peritoneal membrane during the long-term peritoneal dialysis with hypertonic glucose solution in rats. METHODS: Eighteen Sprague-Dawley male rats were randomly divided into 2 groups: control rats (n=6) with peritoneal catheter but not dialyzed; rats with peritoneal dialysis (PD) (n=12) were dialyzed with 4.25% glucose dialysate for all exchanges. Before completion of the study, 4 animals in PD group were euthanized owing to nonfunctional catheters or peritonitis, leaving 14 animals for the analysis. Dialysis exchanges were performed 3 times a day with 25 mL/each exchange for 12 weeks. Immunoperoxidase staining was performed using monoclonal anti-AGE antibody and polyclonal anti-AQP-1 antibody. The slides were read by 5 different examiners in a blind fashion. The staining intensity was graded semiquantitively from 0 to 3. The peritoneal membrane function was assessed by performing one-hour peritoneal equilibration tests every 6 week for comparing transport characteristics. Peritoneal membrane transport rate was assessed by D/P of urea nitrogen and D/Do of glucose. Water transport of peritoneal membrane was assessed by D/P of sodium at 12 week. RESULTS: The expression of peritoneal AQP-1 was increased in rats with PD, compared to control rats. Consistent with this, D/P of sodium in rats with PD was significantly decreased compared to control rats (0.58+/-0.04 vs 0.86+/-0.07, p<0.05), indicating high peritoneal water permeability in response to long-term peritoneal dialysis. Moreover, rats with PD were associated with significantly lower D/Do of glucose and higher D/P of urea nitrogen, suggesting high peritoneal membrane transport. CONCLUSION: High expression of peritoneal AQP-1 was associated with an increased peritoneal water permeability in response to long-term peritoneal dialysis with 4.25% glucose for 12 weeks. The underlying mechanisms for the increased AQP-1 expression need to be examined whether it is due to the continuous exposure to the dialysis solution containing high glucose concentration itself or compensatory effects of slowly developed concomitant ultrafiltration failure in chronic peritoneal dialysis.