Early Enhancement by Thyrotropin of Thyroid Organification of Circulating Iodide11

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Abstract
The early effect of thyrotrophin (TSH) upon thyroid uptake and organification of various doses of iodide was studied by giving I131-labeled iodide of known specific activity as a single injection to Purina-fed rats, followed by TSH or saline intravenously. Three hr. later thyroid concentration and proportion of protein-bound iodine (PBI131) and iodide-I131 were determined by paper chromatography and glandular content of newly formed PBI131 calculated from the specific activity of the iodide given. At the 5 [mu]g iodide dose, glandular uptake and PBI127 concentration were the same in TSH and control groups. When 50-5000 [mu]g of iodide was given, TSH enhanced glandular uptake and PBI127 formation. The increment in PBI included both iodotyrosines and iodothyronines and was not abolished by per chlorate. At the higher iodide doses, PBI formation was severely depressed in controls (Wolff-Chaikoff effect) but was unimpaired in the TSH group. The results suggest that, under these conditions. TSH promptly stimulates uptake and organification more resistant to the inhibitive effect of higher plasma iodide concentrations.

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