Effect of Hypothyroidism on Bone Repair in Mature Female Rats

T hyr oid hormones are major regulatorsof bone metabolism and development.In hyperthyroidism, bone resorption isincreased, however, the mechanism bywhich thyroid hormones increase osteoclasts activityand its growth remains unknown. This researchwas designed to study the effect of hypothyroidismon the bone repair.Materials and Methods: Sixty mature female ratswere randomly divided into two groups: controland methimalole treated groups. In the methimazoletreated group, hypothyroidism was induced.Medial surfaces of right tibia of controland methimazole treated groups were drilled; allthe rats were killed after three weeks by choloroforminhalation. Bone samples were obtainedfrom defected regions and were subjected to histomorphometricstudy.Results: The weight, length and periosteumthickness of tibia of the rats were significantlydecreased in methimazole treated group as comparedto the controls. There was significant decreasein osteoblast numbers (19.2±3.6 vs34.l±3.1, p O.OOl) and increase in the numbers ofosteoclasts (5.9 ± 1.6 vs 2.3±1.1, p O.OOl) of themethimazole treated group compared to,the controlgroup.Conclusion: This study demonstrates that hypothyroidismdelays bone remodeling and repairin rat .