Changes in aquaporin (AQP)2 and AQP3 expression in ovariectomized rat urinary bladder: potential implication of water permeability in urinary bladder

Abstract

AQPs have recently been reported to be expressed in rat and human urothelium. The purpose of this study was to investigate the effect of ovariectomy on the expression of AQP2 and AQP3 in rat urothelium. Female Sprague-Dawley rats were divided into three groups: control, bilateral ovariectomy (Ovx), and bilateral ovariectomy followed by subcutaneous injections of 17β-estradiol (Ovx + Est). After 4 weeks, urodynamic studies were done to measure the contraction interval and contraction pressure. The expression and cellular localization of AQP2 and AQP3 were determined by Western blot and immunohistochemistry in rat urinary bladder. In cystometrograms, the contraction interval (min) was significantly lower in the Ovx group (2.8 ± 0.32) than in the control group (5.1 ± 0.56) but was increased after estrogen treatment (8.8 ± 0.29). Conversely, the average contraction pressure (mmHg) was higher in the Ovx group (28.2 ± 2.3) than in the control group (22.3 ± 1.06) and decreased after estrogen treatment (23.1 ± 2.02). AQP2 expression was localized in the cytoplasm of the epithelium, whereas AQP3 was found only in the cell membrane of the epithelium. The protein expression of both AQP2 and AQP3 was significantly lower after ovariectomy and was restored to the control levels after 17β-estradiol treatment. Hormonal alteration causes a significant change in the expression of AQP2 and AQP3. These findings suggest that AQPs might have a functional role in the detrusor overactivity that occurs in association with hormonal alteration in female rat.