Selective decrease in urinary aquaporin 2 and increase in prostaglandin E2 excretion is associated with postobstructive polyuria in human congenital hydronephrosis

This study was undertaken to determine the role of aquaporin 2 (AQP2) in the impaired urinary concentrating capacity observed in patients who underwent pyeloplasty because of congenital unilateral hydronephrosis as a result of pyeloureteral junction disease. Twelve children (mean age, 8 ± 2 mo) were examined in the study. From day 1 to day 5 after surgery, the urine was collected separately from pyelostomy draining only from the postobstructed kidney and from the bladder catheter draining mostly from the contralateral kidney used as internal control. After pyeloplasty, the postobstructed kidney was characterized by a reduced urinary excretion of AQP2 (∼54%) associated with polyuria that persisted from day 1 to day 5 (433 ± 58 versus 310 ± 74 ml/24 h at day 1; 326 ± 44 versus 227 ± 26 ml/24 h at day 5). In parallel, urine osmolality from the postobstructed kidney was significantly reduced compared with the contralateral kidney (111 ± 12 versus 206 ± 49 at day 1; 136 ± 24 versus 235 ± 65 mOsm/kg at day 5). Creatinine clearance from the postobstructed kidney was not significantly different compared with the contralateral kidney throughout the 4 d after surgery. However, on day 5, creatinine clearance from the postobstructed kidney became significantly lower. Prostaglandin E2 in the urine from postobstructed kidneys was found to be twofold higher than in the contralateral samples (26.0 ± 6.7 versus 13.5 ± 2.5 at day 5). It is concluded that (1) the selective downregulation of AQP2 in postobstructed kidney may account for the higher excretion of hypotonic urine, and (2) the local increase in prostaglandin E2 synthesis in postobstructed kidney may be involved in AQP2 downregulation and in maintaining a GFR similar to that of the contralateral kidney.