EFFECT OF VARYING IODINE SUPPLY ON LABELLED IODINE FRACTIONS IN THE THYROID GLAND AFTER I131 ADMINISTRATION

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Abstract
Rats on a low I diet, 0.1 [mu]g I/g food, have a higher uptake of I131 in the thyroid and also a more rapid release of I131 from the gland than animals on an I rich diet. The proportion of radioiodine in thyroid hydrolysates found as monoiodotyrosine and diiodotyrosine decreased with the time elapsing after injection of the tracer dose and the decrease was more rapid in animals on the low I diet. The ratio of I131 in monoiodotyrosine to I131 in diiodotyrosine did not significantly change with time from 30 minutes to 7 days after the injection of I131. This ratio was much higher in animals on a low I diet than in animals on an I rich diet. The proportion of thyroid I131 found in the 2 fractions usually called thyroxine and triiodothyronine in butanol-dioxane-ammonia chromatograms increased with the time elapsing after injection of I131. Again this increase was more rapid in the animals on the low I diet. Possible mechanisms explaining these observations are discussed.