Transport of thyroxine in the serum of vitamin A-deficient rats.

Thyroxine (T4) transport in the serum of rats deficient in vitamin A was studied by electrophoresis after incubation of serum samples with radioactive T4. In serum from vitamin A-deficient rats, the amount of radioactivity bound to the prealbumin zone of the electrophoretograms decreased, whereas there was an increase in the amount of radioactivity bound to the albumin zone. The serum from vitamin A-deficient rats subsequently fed a normal diet (repletion experiment) had an electrophoretic pattern similar to that of normal rats. The serum fraction which bound radioactive T4 appeared in the prealbumin rather than the albumin zone. These results suggest that vitamin A deficiency causes an early change in the transport of thyroid hormones in the plasma and a new level of serum thyroxine which may be responsible for the biochemical and physiological changes which occur in vitamin A-deficient rats.