Maintenance of Skeletal Growth and Maturation in Thyroidectomized Rats by Injection of Iodide

Abstract

Female rats of the Long-Evans strain were thyroidectomized when 26 days of age by a combination of surgery and I¹³¹. Injection of iodide (5 mg/day, as KI) was started immediately, and its effect on skeletal growth and maturation was compared simultaneously with that achieved by L-thyroxine replacement therapy (0.25 μg/day) during and at the end of 2 months of injection. Growth was measured by increases in body and tibia length, as shown in roentgenograms taken at intervals during the experiment, and by the width and histology of the proximal epiphysial plate of the tibia at autopsy. Increase in body weight gave additional confirmatory evidence. Maturation was evaluated by examination of selected ossification centers shown in the roentgenograms. The terminal skeletal age assigned each rat on this basis was verified by study of dissected bones. Vigorous and identical growth, at a nearly normal rate, was maintained in both treated groups throughout the experimental period, as contrasted with the severe retardation that characterized the thyroidectomized controls. Furthermore, tibia length maintained normal proportionality to body length in the treated groups. The width of the epiphysial plate of the tibia after either treatment, although slightly less than normal, was substantially wider than in the thyroidectomized controls. As in the normal, endochondral osteogenesis was active, contrasting sharply with the markedly reduced activity in thyroidectomized controls. Maturation, like growth, was influenced to the same extent by thyroxine and iodide, in that there was a progressive and continuous increase in skeletal age considerably above thyroidectomized controls although slightly less than normal. It is concluded that balanced skeletal growth and maturation can be maintained in thyroidectomized rats by a minute quantity of thyroxine or a large quantity of iodide.