Hypothalamic Influence on Thyroxine Monodeiodination by Rat Anterior Pituitary Gland

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Abstract
In order to determine if the monodeiodination of I131-labeled thyroxine (Tf) to 3, 5,3''-triiodothyronine (T3 which occurs in the anterior pituitary is dependent upon hypothalamic influences, the metabolic fate of T + in intraocular pituitary transplants has been examined chromatographically. Concentration of total radioactivity in the transplants was similar to that of the normal in situ pituitary, but the proportion of T3 was much reduced. In normal rat anterior pituitary, the relative amount of T3 was 17% of the total radioactivity in 2 experiments transplants, on the other hand, showed no T3 in one experiment and 9% in a second. In thyroidectomized rats the relative proportion of T3 in the anterior pituitary rose to 26%. These findings are interpreted to indicate that monodeiodination of T4 to T3 is related to the functional activity of the anterior pituitary and that this activity depends upon intact hypothalamic-pituitary connections.