P. Rudas et al., THYROID-HORMONE DEIODINATION IN THE BRAIN OF YOUNG CHICKENS ACUTELY ADAPTS TO CHANGES IN THYROID STATUS, Acta veterinaria Hungarica, 41(3-4), 1993, pp. 381-393
The brain represents a special organ in respect of thyroid hormone han
dling. This was analyzed in one-week-old chickens. The effect of sham-
operation (SH), thyroidectomy (TX) and thyroidectomy plus thyroxine su
pplementation (TX+T4) on the intracerebral triiodothyronine (T3) conte
nt and on the activity of different types of deiodinases was investiga
ted. it was found that in spite of very low T3 levels in the serum of
TX animals, the brain displayed close to normal tissue T3 levels. Kine
tic studies of the deiodinase system showed an increase in type II act
ivity (increased T4 to T3 conversion) and decreased type III activity
(decreased degradation of intracellular T3) in the brain of TX animals
vs. SH or TX+T4. It is concluded that a considerable part, if not the
total of the T3 preserved in hypothyroidism may be ascribed to adapti
ve changes of the deiodinase system in the brain of young chickens.