Effects of hyper- and hypothyroidism on the development and proliferation of testicular cells in prepubertal rats.

Thyroid hormones are important in the development and regulation of testes. This study was conducted to determine the effects of hyper- and hypothyroidism on testicular development in prepubertal rats aged 20-70 days. Weaning male rats (20 days old) until day 70 age were randomly divided into four groups: control, hyperthyroid (hyper-T), hypothyroid (hypo-T) and hypothyroid treated with thyroxine (T4) (hypo-T+T4). The results indicated that thyroid hormones caused a significant effect in body and testis weights, and food and water consumption. In addition there were changes in serum concentrations of tri-iodothyronine, T4, thyroid stimulating hormone (TSH) and testosterone. Histomorphology showed a significant decrease in seminiferous tubule diameter in hyper-T compared to the other groups. Leydig cell numbers showed a significant elevation in hyper-T but not in hypo-T groups. Immunostaining indicated that TSH receptor (TSHR), thyroid hormone receptors α/β (TRαβ) and proliferating cell nuclear antigen (PCNA) have the roles in testicular development. Our findings suggest that hyper- and hypo-thyroidism regulate testicular cell proliferation and spermatogenesis in prepubertal rats, indicating that expression of TSHR, TRαβ and PCNA may be regulated by thyroid hormones that are involved in testicular development; and that the administration of T4 to the hypo-T+T4 group leads to an improvement in the testicular condition.