Effect of Dinitrophenol Administration on the Transport and Metabolism of the Thyroid Hormones in Rats

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Abstract
Dinitrophenol administration to intact and thyroidectomized (L-thyroxine maintained) rats produced a 50% decrease in the serum protein-bound iodine and a significant decrease in the amount of I131-labeled thyroxine bound to the thyroxine-binding protein as determined by starch gel electrophoresis. The addition of dinitrophenol to rat sera produced a similar effect on thyroxine binding. Following the ip injection of 1 [mu]c of I131-labeled thyroxine, the total retained radio-activity in thyroidectomized stabilized rats was measured 3 times daily for 14 consecutive days. This was done by using a large well liquid scintillation counter (Armac). The disappearance of radioactivity from the whole animal may be represented as 2 major components, an initial fast component with a biological half-life of 24 hr. and a second and slower component with a half-life of 113 hr. The slower component became apparent on the 5th day, by which time 85% of the administered radioactivity had been excreted. Dinitrophenol administration altered the rate of disappearance of radioactive thyroxine. In the DNP-treated rats the fast component had a half-life of 12 hr. and the second component had a half-life of 185 hr. The alterations in the disappearance of I131-T4 may be due to changes in the binding of thyroxine to the serum proteins induced by dinitrophenol.