PURPOSE: The purposes of this study were to investigate the effect of hormonal alterations on the expression of caveolin-1 in the urinary bladders of ovariectomized rats and to determine the role of caveolin-1 in the overactivity of the detrusor muscle that occurs with hormonal alterations in rats. METHODS: Female Sprague-Dawley rats were divided into three groups: a control group, a group that underwent bilateral ovariectomy (Ovx), and a group that underwent bilateral ovariectomy followed by subcutaneous injections of 17beta-estradiol (Ovx+Est). After 4 weeks, urodynamic studies were done to measure the contraction interval and contraction pressure. The expression and cellular localization of caveolin-1 were determined by Western blot and immunofluorescence in the urinary bladders of rats. RESULTS: On cystometrograms, the contraction interval was significantly shorter in the Ovx group (3.0+/-0.3 minute) than in the control group (5.6+/-0.5 minute) but was longer in the Ovx+Est group (9.2+/- 0.4 minute) (P<0.05). Conversely, the average contraction pressure was higher in the Ovx group (26.4+/-0.48 mmHg) than in the control group (21.8+/-0.37 mmHg) but was lower in the Ovx+Est group (23.9+/-0.76 mmHg) (P<0.05). Caveolin-1 was expressed in the capillaries, arterioles, and venules. Expression of the protein caveolin-1 was significantly lower after ovariectomy and was restored to control levels after treatment with 17beta-estradiol (P<0.05). CONCLUSIONS: Hormonal alterations cause a significant change in the expression of caveolin-1, which suggests that caveolin-1 might have a functional role in the overactivity of the detrusor muscle related to hormonal alterations in the urinary bladders of rats.