Effect Of Subclinical Hypothyroidism On Bone Metabolismand Improvement In The Short-term L-Thyroxine Therapy

Objective: Subclinical thyroid dysfunction might influence a bone health. We evaluated whether subclinical hypothyroidism adversely affects bone health including bone mineral density(BMD), and observe lipid metabolism in SCH rats and the relationship between the disorder of lipid metabolism and bone metabolism and the effect of L-thyroxine(L-T4) treatment on these changes in the short term.Method: Twenty male Wistar rats SCH, SCH+T4 and control groups were established. SCH was induced in rats by continuous administration of 5 mg.kg-1.d-1methimazole(MMI) by gavage for three months. The SCH+T4 rats were prepared with the same administration for three months and administered 5 μg.kg-1.d-1L-T4 after 45 days of administration of MMI. The control rats were administered water via gavage.Result:The SCH group displayed higher thyroid-stimulating hormone(TSH), total cholesterol(TC), low-density lipoprotein cholesterol(LDL-C) than the control and SCH+T4 groups. While, Serum total triiodothyronin(TT3) and total thyroxin(TT4)levels were within normal range. Body weight, bone alkaline phosphatase(BALP),tartrate resistant acid phosphatase(TRACP), bone mineral density(BMD) were significantly lower in the SCH group than in the control and SCH+T4 groups.Pearson correlation analysis showed that TSH was positively correlated with TC and LDL-C, and negative correlation with BALP and TRACP. In addition, TC was negative correlation with BMD.Conclusion: In conclusion, the results of this study indicate that SCH is closely associated with osteoporosis and lipid metabolism disorder which were partly improved by L-T4 treatment. Lipid metabolism disorder and elevated TSH interaction might be involved in the process of the occurrence of osteoporosis in SCH. There is also another possibility that is the direct causes of osteoporosis in SCH is perhaps the disorder of lipid metabolism and TSH is just cause the disorder of lipid metabolism. In the short term treatment, BMD is neither increased nor decreased after treatment.