Effect of long-time administration of tibolone on vaginal cytology of castrated rats.

PURPOSE: To evaluate the estrogenic effect of tibolone administered at high-dose and long-term through cytological examination of vaginal epithelium of castrated rats. METHODS: 15 adult Wistar rats were submitted to bilateral oophorectomy 30 days before starting the experiment. The rats were then randomly divided in two groups. Experimental rats (n = 9) orally received 1 mg tibolone/day; control rats (n = 6) just received carboxymethylcellulose. Vaginal smears were collected from all rats on days 0, 1-6, 30, 60, 90 and 120 of the experiment. RESULTS: On day 0, smears from all rats were atrophic, classified as anestrus, and remained this type in the control group until day 120. In the tibolone group, on day 3 all the rats had vaginal cytology similar to estrus and maintained the same aspect till day 90. CONCLUSION: Tibolone has estrogenic action in the vaginal epithelium which is already evident after the first dose and remains without major changes over time.