Functional development and maturation of the rat thyroid gland in the foetal and newborn periods: an immunohistochemical study.

Immunohistochemical detection of T4, T3 and thyroglobulin (Tg) was undertaken in foetal and neonatal rat thyroid glands in an attempt to elucidate the functional development and maturation of the gland during these periods. Immunoreactive Tg first appeared in the cytoplasm of the immature thyroid epithelium on the 15th day of gestation, followed by the occurrence of T4 and T3 in the lumen of primitive follicles of the thyroid gland 2 days later. The stainability of Tg, T4 and T3 increased as the follicular structure became mature; however, no significant difference in staining patterns was observed during the perinatal periods.