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The effect of various concentrations of thiourea on the synthesis of thyroxine by the starry flounder, Platichthys Stellatus Kinnear, John Edward

Abstract

The effect of various concentrations of thiourea on the production of thyroid hormones was investigated in the starry flounder, Platichthys stellatus. Flounder were immersed in sea water solutions of thiourea in concentrations of 0.0001%, 0.0005%, 0.001% and 0.0025% for periods of 10 - 11 days and in concentrations 0.005%, 0.01%, 0.02% and 0.03% for as long as 74 days. After injections of tracer doses of radioiodine, extracts of the thyroid glands were subjected to autoradiochromatography. It was established that concentrations of thiourea ranging from 0.0025% - 0.03% completely inhibited the synthesis of the thyroid hormones throughout the course of the experiments. Although the synthesis of the thyroid hormones was abolished in flounder exposed to 0.0025% and higher concentrations of thiourea, flounder in some instances were able to synthesize moniodotyrosine and diiodotyrosine. The significance of this phenomenon is discussed in connection with biosynthesis of the thyroid hormones and the mechanism of antithyroid activity of thiourea. Measurement of the percentage uptake of the injected dose of radioiodine revealed that inhibited flounder consistently had lower values in the thyroid when compared to controls.

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