IMPAIRED GERM-CELL DEVELOPMENT IN THE TESTES OF IMMATURE RATS WITH NEONATAL-HYPOTHYROIDISM

The induction of neonatal hypothyroidism from day 1 to day 25 postpart um using 6-propyl-2-thiouracil (PTU) resulted in a 45% and 77% reducti on of testis weight on days 20 and 30, respectively, and an increase i n Sertoli cell number. The present study evaluated the effect of neona tal hypothyroidism on the developing germ cell population during the f irst 30 days postnatally. Qualitative and quantitative studies using t he optical disector method were undertaken on the testes of control an d hypothyroid rats, on days 10, 20, and 30 after birth. Germ cell deve lopment was obviously impaired in the hypothyroid rats, as shown by de creased primary spermatocyte and round spermatid numbers in day 20 and day 30 testes, and the persistence of gonocytes on days 10 and 20. Th ese reductions obviously accounted for the reduced testis weight, abso lute volume, and diameter of the seminiferous cords/tubules, especiall y on days 20 and 30. The failure to establish a seminiferous tubule lu men in hypothyroid rats probably reflects decreased fluid production a nd a functional immaturity of the Sertoli cells. The delay in germ cel l maturation and increased degeneration may be because of the immature state of the Sertoli cell or result from the low follicle-stimulating hormone and thyroxine levels known to occur in the hypothyroid rats.