Changes of Expression of Renal Aquaporin-2 and Na-K-2Cl Cotransporter in Bilateral Ureteral Obstruction (BUO) Rat after Release of BUO and the Effect of Antidiuretic Hormone

Shin, Jinho; Sung, Su Ah; Seo, Ji A; Han, Kum Hyun; Cho, Won Yong; Pyo, Heui Jung; Yoo, Kee Hwan; Won, Nam Hee

Abstract

BACKGROUND
Bilateral ureteral obstuction (BUO) has been known to decrease the expression of renal aquaporin-2 (AQP2) and Na-K-2Cl cotransporter (NKCC2). The polyuria and urinary concentration defect in postobstructive diuresis (POD) may be explained by these molecular changes. By contrast, chronic infusion of antidiuretic hormone (ADH) has been known to increase the expression of renal AQP2 and NKCC2, but there have been no studies regarding the chronic effect of ADH in molecular level when introducing to POD. We tried to identify the changes of renal expression of AQP2 and NKCC2 in 24 hour BUO rat at POD-7 day and the chronic effect of ADH to the expression of AQP2 and NKCC2 in sham operation rat and in 24 hour BUO rat, at sham operation 7 day and at POD-7 day, respectively. METHODS: Twenty four Spraugue-Dawley rats were divided into four groups. Group I (Control group): sham operation rats(n=6). Group II (BUO group): 24 hour BUO and release of it (n=6). Group III (dDAVP group): dDAVP (1-deamino-8d-arginine vasopressin: V2-receptor-selective agonist) infusion at rate of 20 ng/hour by osmotic minipump subcutaneously for 7 days in sham operation rats (n=6). Group IV (BUO+dDAVP group): dDAVP infusion at rate of 20 ng/hour by osmotic minipump by same method as Group III in 24 hour BUO rats (n=6). All rats were sacrificed at POD-7 day (Group II, Group IV) or sham operation-7 day (Group I, Group III) and renal expression of AQP2 and NKCC2 were analyzed by immunohistochemistry and by Western blot method. Blood and urinary chemistry examinations were done concurrently. RESULTS: BUO group showed increased urine output and decreased urine osmolality (p<0.05) and decreased expressions of AQP2 and NKCC2 compared with Control group {29.1 +/- 4.2% vs. 100 +/- 10.0% (p< 0.05); 40.2 +/- 5.4% vs. 100 +/- 7.9% (p<0.05) respectively}. dDAVP group had decreased urine output from POD-1 day to POD-5 day and increased urine osmolality (p<0.05) POD-1 day to POD-7 day during and increased expressions of AQP2 and NKCC2 compared with Control group {206.5 +/- 19.0% vs. 100 +/- 10.0% (p<0.05); 180.6 +/- 13.3% vs. 100 +/- 7.9% (p<0.05) respectively}. But BUO group showed no difference in urine output and urine osmolality and expressions of AQP2 and NKCC2 compared with BUO+dDAVP group {29.1 +/- 4.2% vs. 42.2 +/- 2.3% (p<0.84); 40.2 +/- 5.4 % vs. 47.9 +/- 4.3% (p<0.91) respectively}. CONCLUSION: BUO and POD show decreased expressions of AQP2 and NKCC2 and the unresponsiveness to chronic ADH infusion may be the pathophysiologic basis of POD such as increased urine output, decreased urine osmolality.