Studies of the calcium accretion rate of bone during immobilization in intact and thyroparathyroidectomized adult rats.

In order to study the role played by the thyroid and the parathyroid glands in the development of osteoporosis induced by immobilization, 153 male adult Sprague-Dawley rats allocated in two groups were used. The animals of one group were thyroparathyroidectomized; those of the other group were left intact. Each group was then divided into two subgroups; in one the right hind leg of the animals were immobilized by an elastic adhesive bandage. The animals were observed for varying periods of time up to 16 weeks. Studies of bone mass and 45Ca accretion rate of the right and left femur and tibia were performed in all animals. The results indicate that disuse osteoporosis occurs in rats in the virtual absence of the thyroid and parathyroid glands. The bone loss of the immobilized femur and tibia was less pronounced in thyroparathyroidectomized rats compared to intact rats. The uptake of 45Ca in bone treated by immobilization as compared to the non-immobilized bone was found to be increased to the same proportion in thyroparathyroidectomized and in intact rats. The calcium-accretion rate of non-immobilized bone was lower in thyroparathyroidectomized than in intact rats. The observations indicate that in the rat the parathyroid and thyroid hormones influence the rate of bone turnover and thereby the rate of development of disuse osteoporosis.