Effect of erythropoietin on the expression and function of renal aquaporin-2 after release of bilateral ureter obstruction in young rats

Objective\r\nTo investigate the effect of erythropoietin (EPO) on the expression of aquaporin-2 (AQP2) in the kidney of young SD rats after release of bilateral ureter obstruction (BUO-R).\r\n\r\n\r\nMethods\r\nThirty-two young SD rats were equally divided into 4 groups randomly (BUO group, BUO-R group, BUO-R+ EPO group and Sham group, 8 rats in each group). The BUO model was built through bilateral ureteral ligation.EPO (500 U/kg) was given to BUO-R+ EPO rats at 2 h after release of BUO, and then repeated 6 h, 12 h, 24 h and 36 h thereafter and the same volume of 9 g/L saline was simultaneously given to BUO-R rats.The Sham group was prepared in parallel by laparotomy and free dissection of bilateral ureters but not ligated.Both side kidneys were harvested 48 h (72 h for Sham group) after release of BUO to examine the effect of EPO on the expression of AQP2 in inner medulla by immunohistochemistry, Real-time PCR and Western blot.The urine samples were collected by using metabolic cage before death.\r\n\r\n\r\nResults\r\nThe osmotic pressure of BUO-R+ EPO group was higher than that of BUO-R group, but lower than that of Sham group (P\u003c0.05). Immunohistochemistry showed that the collecting duct wall thinned and lumen enlarged.After the pictures were analysized by using Image-Pro Plus software, it showed that the expression of AQP2 in collecting duct in BUO group was significantly down-regulated compared with that in Sham group, whereas, it was slightly weaker in BUO-R group and BUO-R+ EPO group than Sham group(P\u003c0.05). These results were further confirmed by adopting Western blot, and the relative quantity of AQP2 in BUO group was also the lowest of the four groups (P\u003c0.05). Real-time PCR showed that the level of AQP2 mRNA in Sham group was (24.30±1.03) folds of BUO group, (10.60±1.05) folds of BUO-R group and (5.70±1.01) folds of BUO-R+ EPO group, respectively.\r\n\r\n\r\nConclusion\r\nEPO could promote not only the recovery of AQP2 mRNA and protein expression but also the recovery of AQP2 function in young BUO-R rats.\r\n\r\n\r\nKey words: \r\nErythropoietin; Ureter obstruction; Aquaporin-2; Kidney