Lack of inhibitory or excitatory effects of sex hormones on the development of normal methylthiouracil-induced goiter in the rat

Abstract

To study a possible etiologic role of sex hormones on the development of simple goiter, estradiol benzoate (EB), testosterone propionate (TP), or methyltestosterone (MT) were administered subcutaneously daily for 14 days to normal rats or rats receiving small doses of methylthiouracil (MTU). In agreement with our previous report, it was found that goiter with normal radioiodine uptake followed the intraperitoneal administration of small doses of MTU. It was also shown that goiter with high radioiodine uptake was produced by large doses of EB (50 or 100 μg.) but not by small doses (1 μg.). Small or large doses of EB have failed to augment the goiter produced by small doses of MTU. Furthermore, unlike the findings in man, large doses of EB failed to increase thyroxine-binding capacity of the plasma proteins in the rat. TP, over a wide range of dose, produced a marked growth of the seminal vesicles, but failed to reduce the size of the normal thyroid or the thyroid stimulated by small doses of MTU. TP also failed to reduce the thyroxine-binding capacity of plasma proteins. Although the data on the rat do not support the hypothesis that sex hormones affect the development of goiter by altering the thyroxine-binding capacity of plasma proteins, the data are not necessarily applicable to the physiology of the human thyroid because of differences in thyroxine-binding proteins between man and rat.