ELIMINATION OF C14-LABELED THYROXINE IN THE BILE, URINE AND EXPIRED AIR OF RATS IN ALTERED THYROID STATES1

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Abstract
Adult male Sprague-Dawley rats were treated with appropriate measures to attain the desired metabolic states. DL-thyroxine-l-Cl4 was administered subcutaneously and the elimination of radioactivity determined in bile, urine, and expired air of hypo-, hyper- and euthyroid animals. Biliary elimination of C14 activity in the control rats amounted to 11.8% of the injected dose within a period of six hours. Desiccated thyroid treated animals showed an increased excretion of radioactivity accompanied with an increased volume of bile produced. The thyroidectomized and thiouracil-treated rats showed no change from normal in the amount of radioactivity eliminated but both groups had a reduction in the volume of bile removed. Urinary excretion of thyroxine activity during the twelve hour period never exceeded 2% of the injected amount regardless of the group studied. Hyper-thyroid animals showed increased urinary excretion of radioactivity with increased volume of urine eliminated. The Cl4 activity in the urine of the thyroidectomized and thiouracil-treated groups was lower than the control animals but only significantly so in the latter case. This reduction in the amount of activity was found to be independent of the urine volume excreted. The recovery of Cl4 in the expired air was taken to indicate that decarboxylation of the administered thyroxine had occurred. Within twelve hours about 12% of the injected activity appeared as C14O2 in the control group. No alteration in this amount was observed in the hyperthvroid animals. Both hypometabolic groups showed decreased Cl4O2 production, however, this was only significant in the thiouracil-treated animals.