Thyroid hormone has some effects on bone and cartilage tissue, but their details have not been explained clearly. Previous studies indicate that the renal tubular reabsorption of phosphate and bone metabolic cycles are enhanced in hyperthyroid states. Recently in Japan, Shimazaki and others reported the ameliorating effect of triiodothyronine on rickets' rats induced by Sttenbock diet and their new rachitogenic diet.
In this study, we examined the effect of triiodothyronine (T3) on rickets' rats induced by HEBP. The 14 days administration of T3 promoted the calcification of the growth-plate cartilage where there had been an increase in thickness due to the inhibition of calcification by the first 7 days administration of HEBP. And that action of T3 almost appeared by the last 7 days administration of T3. As our studies about the effect of vitamin D metabolites on HEBP induced rickets' rats, the action of T3 was similar to that of cholecalciferol and 1, 25 (OH) 2D3. But the action of T3 is thought to be direct to bone and cartilage tissue by our investigation of serum values of their rats.