NATURE OF THE I131COMPOUNDS APPEARING IN THE THYROID VEIN AFTER INJECTION OF IODIDE-I13112

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Abstract
A study was made of the nature of the 1131-compounds appearing in the thyroid vein of 7 sheep, 1 horse, and 1 dairy calf, all of which had been injected with large doses of 1131. Thyroid venous plasma, carotid arterial plasma, and thyroid tissue, obtained simultaneously, were examined by filter paper chromatography. To detect weak 1131-containing components in plasma, such as triiodothyronine and iodotyrosines, concentrated butanol extracts of plasma were first prepared before chromatography. Whole plasma was always chromatographed for comparison. 1131-triiodothyronine was more readily detectable in the thyroid vein than in the peripheral circulation. In the thyroid vein, 1131-triiodothyronine was present to the extent of 10 to 20% of the 1131-thyroxine. Similar values were obtained for the ratio of the 2 compounds in the thyroid. Both 1131-thyroxine and ll31-triiodothyronine were generally present in higher concentration in the thyroid vein than in the carotid artery, indicating that the latter compound as well as the former, is secreted by the thyroid gland into the circulation. Iodide-1131, on the other hand, was always more concentrated in the artery than in the vein, indicating active uptake of iodide by the thyroid. No 1131-thyroxine was detected in the thyroid vein of the calf 20 hours after 1131 injection. Over 70% of the 1131 in this case was in the form of a component which remained at the origin of the chromatogram, a characteristic of 1131-thyroglobulin or other 1131-proteins. A component with similar mobility was found in appreciable amounts in the thyroid vein of one sheep. A consistent finding in all animals was the almost complete absence of 1131-iodotyrosines from the thyroid vein, even at times when the thyroid itself contained 70% or more of its I131 in this form. Mono- and diiodotyrosine do not leave the thyroid as such.

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