Effect of methimazole-induced hypothyroidism on serum levels of LH and testosterone and weights of testes and thyroid gland in rat

Thyroid hormones play an important role in the regulation of metabolism, maturity and reproduction. Thyroid dysfunction affects almost all endocrine glands such as pituitary and testis. The aim of this study was to investigate alterations of testosterone and luteinizing hormone (LH) serum levels as well as weights of thyroid gland and testes in methimazole (MMI)-induced hypothyroidism. Twenty-one adult male rats weighing 185 g were divided into 3 groups. The control group received drinking water, while treated groups received two doses of methimazole; low dose (20 mg/dl in drinking water) and high dose (100 mg/dl in drinking water), for 42 days. At the end of the experiments, rats were anesthetized and sacrificed and serum samples were obtained. Serum levels of hormones were measured by radioimmunoassay. Weights of testes and thyroid gland were determined after sacrifice. Results showed that the use of methimazole decreased serum levels of T4, T3, testosterone and LH as well as the weight of testes, while it increased the weight of thyroid gland compared to control group. These effects were more clear in the high dose group. This study suggests that MMI–induced hypothyroidism causes a significant decrease in serum levels of thyroid hormones, testosterone and LH. Hypothyroidism also decreases the weight of testes, while it increases the weight of thyroid in rat. These effects were dose-dependent.