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Effects of Thyroid Hormone Administration and Estrogen Deficiency on Bone Mass of Female Rats
Author(s) -
Gouveia Cecilia H. A.,
Jorgetti Vanda,
Bianco Antonio C.
Publication year - 1997
Publication title -
journal of bone and mineral research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.882
H-Index - 241
eISSN - 1523-4681
pISSN - 0884-0431
DOI - 10.1359/jbmr.1997.12.12.2098
Subject(s) - endocrinology , medicine , ovariectomized rat , bone mineral , estrogen , skeleton (computer programming) , osteoporosis , bone density , lumbar vertebrae , dual energy x ray absorptiometry , osteopenia , lumbar , surgery , anatomy
To investigate the effects of thyroxine (T 4 ) administration on bone mass, five 81‐day‐old female rats were treated with T 4 (25 μg of T 4 /100 g of body weight [bw]/day), and bone mineral density (BMD) was measured by dual‐energy X‐ray absorptiometry (DXA) 28 days later. The BMD values for the total skeleton, femoral, and tibial subsegments were lower than in controls ( p ≤ 0.05). The lumbar spine (L2–L5) was not significantly affected by T 4 treatment. Next, thirty‐seven 211 ± 1.5 (mean ± SEM)‐day‐old female rats were divided into six groups as follows: (1) control; (2) ovariectomized (OVX); (3) 1xT 4 (∼1.0 μg of T 4 /100 g of bw/day; approximately physiological replacement dose); (4) OVX+1xT 4 ; (5) 2xT 4 (∼2.0 μg of T 4 /100 g of bw/day); (6) OVX+2xT 4 . DXA scans were performed at days 0 and 85. Control rats showed a generalized BMD increase, as opposed to a decrease in OVX rats. The trabecular bone volume of the fifth lumbar vertebra was also lower in OVX rats than in controls ( p < 0.05). The 1xT 4 treatment had no effect on BMD of intact rats, while treatment with 2xT 4 impaired the expected BMD increase. Unexpectedly, the OVX+1xT 4 group presented a generalized BMD increase that was significant for the total skeleton, L2–L5, and femoral subsegments ( p < 0.05), comparable to controls. Treating OVX animals with 2xT4 did not potentiate the osteopenic effects of estrogen deficiency, nor did it reverse the osteopenic effects of OVX. In conclusion, treatment with high doses of T 4 caused BMD to decrease substantially, particularly at the femur, whereas near physiological doses of T 4 prevented bone loss associated with OVX, and regardless of bone type (trabecular or cortical), the skeleton site seems to be a more important determinant of the effects of thyroid hormone on bone mass.