THYROXINE AND TRIIODOTHYRONINE UPTAKE BY THE BRAIN OF CHICKENS

The instant uptake of 125-I-labelled triiodothyronine and 125-I-thyrox ine by the brain tissue was measured in sham-operated (SH) controls, t hyroidectomized (TX) and thyroidectomized plus iodothyronine supplemen ted (TX+T3 or TX+T4) young chickens. It was found that thyroidectomy s ignificantly increases the uptake of iodothyronines, and iodothyronine supplementation returns the uptake close to sham-operated levels. The characteristics of the inhibition of the uptake of labelled hormones by non-labelled iodothyronines speak in favour of the presence of spec ific, separate uptake sites for T3 and T4 in the blood-brain barrier o f young chickens.