Thyroid Hormone Regulates Postnatal Development of the Rete Testis in Mice

Thyroid hormone regulates the rate of testis maturation in mammals. Manipulations of thyroid hormone levels in neonatal animals affect various aspects of testis biology. However, there have been no studies examining the effects of thyroid hormone on the rete testis (RT). Here, we used animal models of neonatal hyperthyroidism (injections of triiodothyronine, or T3) and hypothyroidism (goitrogen 6-propyl-2-thiouracil [PTU] treatment) and found that higher levels of thyroid hormone accelerate RT development, while lower levels of thyroid hormone delay it. T3 and PTU treatments influence RT size, proliferation of RT cells, and expression of DMRT1 and androgen receptor in the RT. T3 supplementation accelerates RT development in an organ testicular culture, which indicates the local action of thyroid hormone. Additionally, it was found that follicle-stimulating hormone could be involved in the regulation both of RT proliferation and RT size. The fact that RT cells in a cell culture do not respond to T3 suggests indirect action of thyroid hormone on the RT in vivo or the loss of the responsiveness to the hormone in vitro.