Thyrotropin and Thyroidal Peroxidase Activity1

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Abstract
In order to investigate the effect of thyrotropin on thyroid peroxidase, changes in the peroxidase activity in response to several in vivo manipulations to change thyroidal iodine metabolism were observed in rats. Most of the peroxidase activity in rat thyroids determined by a guaiacol assay was found in a mitochondrial–microsomal fraction, and the activity was not increased by solubilization of the enzyme with 1% digitonin. Manipulations included the acute administration of 1 USP unit of TSH, 3 mg of propylthiouracil (PTU) and 200 mg of perchlorate (C1O4-), and the chronic administration of 2 USP units of TSH, 3 mg of PTU, 200 mg of CIO4-, 5 ng of triiodothyronine (T3) and T3 plus PTU daily for 7 days. The peroxidase activity per thyroid and per unit of deoxyribonucleic acid (DNA) was not changed by any of the acute manipulations. However, the chronic administration of TSH, PTU and C1O4∼ significantly increased, and T3 and T3 plus PTU significantly decreased the activity. These results suggest that TSH i...

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