PLASMA I131-THYROXINE IN HYPOPHYSECTOMIZBD RATS INJECTED WITH RADIOIODIDE1

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Abstract
Hypophysectomized rats on low- or regular iodine diet were injected with large doses of I131 (250 to 1,000 μC), either with or without iodide carrier. Plasma was obtained 90 to 96 hours later, and dialyzed to remove inorganic iodide. Concentrated butanol extracts of plasma and of pancreatin digests of plasma were chromatographed, and distribution of I131 on the chromatograms was determined by counting sections of the paper in a scintillation well-counter, by use of an automatic paper scanner, or by radioautography. I131-thyroxine was detected in the plasma of the hypophysectomized rats but, in relation to the injected dose of I131, it was less than 1% of the amount observed in normal control rats injected with 1 or 5 μe. of I131. This low level of I131-thyroxine probably reflects a small residual thyroid function in hypophysectomized rats, although interpretation of the results was complicated by radiation damage to the thyroid.