Factors Affecting Exchange of Thyroid Hormones Between Liver and Blood

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Abstract
Radio-actively labeled thyroxtne was administered to rats, and after 1 to 20 hr. their livers were isolated and perfused with pooled rat blood. It was found that, during the perfusion, unchanged T4 was released to the perfusing blood. The efflux of T4 from liver to blood was decreased by the addition of sodium sailcylate to the perfusing blood and was reversed by the addition of 2 mg of stable T4 to the perfusate. When T4 in liver and blood had approached an equilibrium, exchange transfusion resulted in a further efflux of T4 from the liver and the establishment of a new equilibrium. The dynamic equilibrium existing between T4 in liver and in blood was shown most dramatically when T4-I131 was In the liver and T4-I125 was in the blood when perfusion of the liver began. Livers from rats given radioactively labeled triiodothyronine (T3) released only a small amount of T3 to the perfusing blood but deiodlnation and conjugation were greater than after administration of T4-I131.