The effect of estradiol (E2) on the urinary bladder of old female rats was investigated by examining the histology and blood flow in the bladders. A total of 20 female Wistar rats aged 16 months were divided into 4 groups: Group I, 5 normal controls; Group II, 5 rats treated with E2 for 4 weeks; Group III, rats treated with E2 for 8 weeks; and Group IV, 5 rats receiving a placebo for 8 weeks. After the treatment, we removed the bladders, then weighed and stained them with hematoxylin and eosin. The muscle content was analyzed with the Elastica-van Gieson method, and the number of blood vessels with the Masson's trichrome method. Blood circulation in the bladders was also measured. The E2-replaced groups showed higher levels than the other groups in terms of blood flow in the bladder (20.6 ± 1.8 mL/min for Group II and 23.4 ± 1.5 mL/min for Group III, both P < 0.05 versus Groups I and IV), muscle content (2.33 ± 0.47 and 3.11 ± 0.48 for Groups II and III, respectively, both P < 0.05 versus Groups I and IV) and bladder weight (185.3 ± 6.2 mg and 193.2 ± 23.5 mg for Groups II and III; Group III showed P < 0.05 versus Groups I and IV). Differences in body weight and number of blood vessels among groups were not significant. We observed an increase in blood circulation, muscle content and weight of the bladder: E2-replacement therapy positively affected bladder functions
