Effect of erythropoietin on the expression and function of renal aquaporin-1 after release of bilateral ureter obstruction in young rats

Abstract

Objective To investigate the effect of erythropoietin(EPO)on the expression and function of aquaporin-1(AQP-1)in the kidney of young male SD rats after release of bilateral ureter obstruction(BUO-R). Methods Forty-eight young SD rats were randomly divided into bilateral ureteral complete obstruction(BUO) group (n=6), BUO-R group (n=12), BUO-R+ EPO group (n=12) and Sham group (n=18). The BUO model was built through bilateral ureteral ligation.BUO group were killed after 24 h, and BUO-R group and BUO-R+ EPO group were relieved after obstruction of 24 h. EPO(500 U/kg)was given to BUO-R+ EPO rats at 1 h after release of BUO, and then repeated 1 d, 3 d and 5 d 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 and blood samples were collected on 3 d and 7 d(24 h, 3 d, 7 d for Sham group) after release of BUO.The urine samples were collected by using metabolic cage before death.The plasma osmotic pressure, creatinine(Cr) and urea nitrogen(BUN) in the plasma of young rats were detected.The expression of AQP-1 protein in all groups of kidney tissues was detected by adopting immunohistochemistry and Western blot. Results On day 3 after release of BUO, 24 h water intake and urine volume of BUO-R+ EPO group were higher than those of Sham group, but lower than those of BUO group(P<0.05), the urine osmotic pressure of BUO-R+ EPO group was higher than that of BUO group, but lower than that of Sham group (P<0.05), while plasma osmotic pressure, Cr and BUN of BUO-R+ EPO group were higher than those of Sham group, but lower than those of BUO group(P<0.05), and they were all of lower than BUO group (P<0.05). On day 7 after release of BUO, there was no obvious change in Sham group, and the indexes of BUO-R group and BUO-R+ EPO group gradually recovered, but they still did not reach the normal level (P<0.05). The difference between BUO-R group and BUO-R+ EPO group was statistically significant (P<0.05). The immunohistochemical results showed that the expression of AQP-1 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 that of Sham group (P<0.05). Compared with 3 days after release of BUO, the staining intensity of BUO-R+ EPO group and BUO-R group was enhanced, but still lower than that of the Sham group.These results were further confirmed by adopting Western blot, and BUO group was also the lowest of the four groups, and BUO-R+ EPO group was higher than that of BUO group, but lower than that of Sham group (P<0.05). Conclusion EPO can promote not only the recovery of AQP-1 protein expression but also the recovery of renal function in young BUO-R rats. Key words: Erythropoietin; Ureter obstruction; Aquaporin-1; Kidney