Free and protein-bound tri-iodothyronine in the serum of vitamin A-deficient rats.

Tri-iodothyronine (T3) transport in the serum of rats on a vitamin A-deficient diet was studied by electrophoresis after the incubation of serum samples with radioactive T3. The level of serum free tri-iodothyronine (fT3) was measured by radioimmunoassay after serum chromatography on Sephadex LH-20 gel. In the serum of control rats a major part of the radioactivity was bound to the albumin zone (61%) and a minor part to the prealbumin zone (32%). In the serum of vitamin A-deficient rats a larger amount of radioactivity was bound to the postalbumin zone; the lower the level of vitamin A in serum, the greater was the radioactivity in this zone of the electrophoretogram. In these animals there was also a negative correlation between the serum vitamin A and the fT3. There was also a positive correlation between the radioactivity bound to the postalbumin zone and the fT3. The possible causes and effects of these modifications in vitamin A-deficient rats are discussed.