[Experimental study of thyroid hormone and bone metabolism in the rat]

Thyroid hormones (T3, T4) stimulate bone turnover. Calcitonin is a potent inhibitor of osteoporostic bone resorption. In patients with thyrotoxicosis, bone mineral content is reduced. We investigated the influence of calcitonin deficiency in thyroidectomized parathyroid-autotransplanted rats with L-thyroxine (T4) supplementation. Thyroidectomy resulted in a reduction of bone volume, bone calcium content and in a decrease in trabecular bone volume. T4-supplementation corrected this loss of bone calcium content but not trabecular bone volume. In thyroidectomized parathyroid-autotransplanted rats matched for T3-levels to intact controls, there was still a reduction in both bone calcium content and trabecular bone volume. We assume this decrease in bone mass in thyroidectomized parathyroid-autotransplanted animals to be caused by the lack of calcitonin.