Effects of Triiodothyronine and Estrogen Administration on Bone Mass, Mineral Content and Bone Strength in Male Rats

Abstract

Experimental hyperthyroidism had a negative effect on bone mineral density, but did not significantly alter mechanical properties of femur and femoral bone thickness. Estradiol at a dose used in humans for the treatment of osteoporosis decreased seminal vesicle weight and concentration of testosterone but increased bone density in male rats compared to intact animals. In these rats, the mechanical analysis revealed an increased mechanical femur strength higher than the increase in bone density and femoral cortical thickness. When hyperthyroid male rats with low bone density were treated with estradiol in spite of a low plasma testosterone, the changes in bone density resulting from hyperthyroidism were entirely prevented. Estrogens protect the male skeleton against resorbing action of T₃. Treatment with estradiol in male rats with hyperthyroidism did not increase mechanical bone strength or femoral cortical thickness as it did with estradiol administration alone. Our results suggest that exogenously administered estrogens may have therapeutic value in preventing bone loss accompanying triiodothyronine administration, even in male rats with a low testosterone levels. At the concentration studied, estradiol increased in spite of low plasma testosterone, bone mineral density, mechanical strength of femur, and femoral cortical thickness.

Key words

Hyperthyroidism - Bone Mineral Density - Mechanical Strength - Estradiol - Male Rats

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