The influence of testosterone on the development of autoimmune thyroiditis in thymectomized and irradiated rats

Orchidectomy was found to potentiate the development of autoimmune thyroiditis induced by thymectomy and irradiation (Tx-X) in male PVG/c strain rats. Conversely, testosterone administration to orchidectomized Tx-X rats markedly reduced or inhibited the development of this condition. When given in varying quantities by injection in oil over a period of 15 weeks the inhibitory effect on the development of both thyroiditis and thyroglobulin autoantibodies was found to be directly related to dose. Levels between 150 ng and 150 micrograms/100 gm body weight reduced the incidence and severity of the disease whilst levels of 500 micrograms and 5000 micrograms abrogated these autoimmune effects. Testosterone in implant form had a similar effect. Low doses of testosterone administered by either procedure were also found to be beneficial to entire female Tx-X rats. These results indicate that sex steroid hormones have an important modulatory influence on the genesis of autoimmune thyroiditis. Furthermore, it is also apparent in this particular model that this influence can be demonstrated in the absence of the thymus gland