Triiodothyronine receptor complex in developing rat brain and pituitary

In vitro saturation analysis combined with nuclear 3,5,3'-triiodothyronine (T3) quantification was used to examine the changes in T3 binding parameters in rat pituitary and cerebrocortical nuclei from fetal day 14 to postnatal day 20. T3 receptors were first detectable in neuronal, glial, and pituitary nuclei on fetal days 14, 17, and 18, respectively. Thereafter T3 receptor concentrations in neuronal, glial, and pituitary nuclei increased throughout the developmental period studied, reaching maximal levels during neonatal life (1,129, 1,025, and 635 fmol/mg DNA, respectively). T3 levels in pituitary, neuronal, and glial nuclei also increased during development there being a 35-, 34-, and 120-fold rise between fetal days 16-18 and the 20th postnatal day. Endogenous T3 receptor occupancy throughout the experimental period increased six- to ninefold in the three types of nuclei. The presence of T3 receptor complex in the pituitary and cerebrocortical nuclei during perinatal development lends further support to the hypothesis that T3 may be an important factor in determining the differentiation and development of these cells.