Effects of hyper- and hypothyroidism on thyroid hormone concentrations in regions of the rat brain.

The purpose of this study was to investigate the effects of hyper- and hypothyroidism on thyroid hormone concentrations and deiodinase activities in nine regions of the rat brain. Four weeks of treatment with 75 microg thyroxine (T4)/kg body wt induced a two- to threefold increase in T4 levels in all of these brain regions, whereas the 3,5,3'-triiodothyronine (T3) concentrations were reduced in five brain regions and remained unchanged in four. Even after 8 wk treatment with 300 microg T4/kg, the T3 concentrations remained normal in cortical areas, the hippocampus and amygdala, and were elevated only in areas in which inner-ring deiodinase activity was low or absent, and in the hypothalamus.

Concentrations of seven iodothyronine metabolites in brain regions and the liver of the adult rat.

The concentrations of the iodothyronine metabolites T(4), T(3), 3,5-diiodothyronine (3,5-T(2)), 3,3'-diiodothyronine (3,3'-T(2)), reverse T(3) (rT(3)), 3,3'-T(2) sulfate (3,3'T(2)S), and T(3) sulfate (T(3)S) were measured in 12 regions of the brain, the pituitary gland, and liver in adult male rats. Quantification of iodothyronine was performed by RIA following a newly developed method of purification and separation by HPLC. 3,5-T(2), 3,3'-T(2), rT(3) and T(2)S were detectable in the low femtomolar range (20-200 fmol/g) in most areas of the rat brain.