RESUMO
BACKGROUND: This study aimed to evaluate the effect of long-term high-dose tibolone on the bladders and urethras of ovariectomized rats. METHODS: Bilateral ovariectomy was performed in 14 young adult rats randomly divided into 2 groups. Experimental rats (n = 9) received 1 mg/day of tibolone orally; control rats (n = 6) received a placebo. After 150 days, the bladders and urethras were removed. Bladder cell proliferation was analyzed by Ki-67 immunohistochemistry. A histomorphometric analysis was performed for epithelial thickness and the percent areas of collagen fibers and blood vessels. Data were compared using a Mann-Whitney test (significance level at p < 0.05). RESULTS: Urothelial thickness and the percent area of collagen fibers and blood vessels were not significantly different between the tibolone and control groups in the bladder and urethra. In addition, urothelium cell proliferation in the bladder showed a low immunopositivity in both groups. Furthermore, the glycogen and glycoprotein contents in urethral epithelium were slightly modified by tibolone and no change was observed in the bladder. CONCLUSION: Long-term administration of tibolone has no effect on urothelial trophism, collagen fibers, the number of vessels, or cell proliferation in the urethra and bladder of the ovariectomized rat.