Neonatal hypothyroidism causes delayed Sertoli cell maturation in rats treated with propylthiouracil: evidence that the Sertoli cell controls testis growth.

BACKGROUND: The testes of rats treated neonatally with propylthiouracil (PTU) grow to almost twice their normal size. The cause of testicular enlargement has been suggested to be the result of delayed maturation of Sertoli cells, allowing Sertoli cell division to occur beyond the 15th postnatal day, the commonly recognized cutoff date for Sertoli cell divisions. It has been shown that an increased population of Sertoli cells in postnatal development supports increased numbers of germ cells in adult animals. After examining developing rats treated neonatally with PTU, we hypothesized that an approximate 10-day delay in maturation was occurring and proceeded to test this hypothesis experimentally. Thus the purpose of this report was to determine if a 10-day delay in maturation could explain the increased numbers of Sertoli cells and increased testis size in PTU-treated animals.
METHODS: Both control animals and animals treated neonatally with PTU N = 5/group were sacrificed at 15 and 25 days of age and prepared for electron microscopy.
RESULTS: Micrographs show and morphometric ultrastructural analysis of numerous parameters demonstrated at the 95% probability level that Sertoli cells from 25-day-old PTU animals are not different in size and most constituents (volume and surface area) from 15-day-old control animals and are less mature than 25-day-old control animals. Mitosis of Sertoli cells was observed in PTU-treated animals in 25-day-old animals but not in age-matched controls. The number of Sertoli cells in 25-day-old PTU-treated animals is significantly increased over age-matched controls. Micrographs show the presence of immature Sertoli cell nuclei in 25-day-old animals receiving PTU as well as increased germ cell degeneration in this group. Sertoli cell tight junction formation is also delayed in PTU-treated animals as compared with controls.
CONCLUSIONS: Together, the data show that delayed maturation of Sertoli cells occurs in treated animals that corresponds to a minimum of 10 developmental days. In the immature state, Sertoli cells continue to divide. Data presented herein and published data related to PTU treatment indicate that delayed maturation of the Sertoli cell results in delayed maturation and proliferation of other testicular cell types. From this and from published data, the hypothesis is presented that the Sertoli cell is responsible for the overall control of testis development.