Histomorfometria do tecido ósseo em ratas castradas tratadas com tibolona

Introduction and objective: The effect of tibolone administered in high dose over a prolonged period was analyzed through histomorphometry of tibia and femur samples from castrated rats. Methods: The experiment was performed in 20 Wistar rats with average weight of 250 g. The animals were randomly divided into three groups: oophorectomized receiving tibolone (OVX + T) (n = 9), oophorectomized (OVX) (n = 6) and non-oophorectomized as control group (C) (n = 5). The experimental protocol was initiated 30 days after oophorectomy and lasted 20 weeks. Tibolone (1 mg/day) was administered to OVX + T rats and carboxymethyl cellulose to OVX. C rats did not go through any treatment. Right side tibias and femurs were fixed in 10% buffered formalin, decalcified and embedded in paraffin. Histological sections were stained by hematoxylin-eosin for histomorphometric analysis. The cortical thickness and medullary cavity were measured in transverse tibia and femur sections. The percentage of porosity and the trabecular density were determined in longitudinal femur sections. Results and discussion: There was no significant statistical difference between OVX and OVX + T in several analyses. The results showed that tibolone did not improve bone quality significantly, although it preserved cortical bone mass in femoral and tibial diaphyses and the trabecular bone in femoral condyles. The administration of tibolone in high dose for a prolonged period may have influenced these effects inasmuch as recent studies have recommended the use of lower doses in osteoporosis prevention. Conclusion: Oophorectomy caused bone loss in the analyzed regions. Despite the fact tibolone did not augment bone mass, this was kept at satisfactory levels.