Developmental delay and unstable state of the testes in the rdw rat with congenital hypothyroidism

From the present study of the rdw rat, it is clear that the thyroid hormone is essential for the development and maintenance of the testes. In previous studies, the thyroid hormone has few serious effects on the testes except during the neonatal stage when the thyroid hormone receptor is mainly present. However, there is little knowledge concerning the prolonged effect of thyroid hormone deficiency throughout the rat's life span. In the present study, a morphological analysis was performed on the testes of rdw rats with congenital hypothyroidism. The rdw testes required a longer time to develop into the normal adult structure. Moreover, the developed, normal structure began to degenerate after full maturation. Specific characteristics of the rdw testes include: (i) a prolonged proliferation of Sertoli cells during postnatal development; (ii) a developmental delay in the appearance of spermatocytes and spermatid; (iii) direct contact with each other for both spermatocytes and spermatids, without Sertoli cell cytoplasm completely intervening between adjacent germ cells; (iv) subsequent apoptosis of germ cells after maturation; (v) reduction in the height of the seminiferous epithelium; and (vi) lower testosterone levels in the rdw rats, especially during old age. Thus, we conclude that the thyroid hormone plays an important role in developing and maintaining normal function of testes.