OBSERVATIONS ON A RELATIONSHIP BETWEEN TOTAL THYROID IODINE CONTENT AND THE IODIDE-CONCENTRATING MECHANISM OF THE THYROID GLAND OF THE RAT1

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Abstract
In hypophysectomized rats receiving thyrotropin in constant doses, the capacity of the thyroid gland to accumulate iodide ion is enhanced by iodine restriction, treatment with propylthiouracil and with potassium thiocyanate. Thiocyanate was withdrawn 24 hrs. before thyroid: serum iodide ratios were measured to allow recovery of the concentrating mechanism from inhibition. A similar reciprocal relationship between iodide-concentrating capacity and total thyroidal iodine concentration was found in intact animals. Evidence is presented in support of the concept that iodide-concentrating capacity is a more sensitive indicator of thyrotropin activity than thyroid weight and it is held unnecessary to hypothesize 2 thyrotropins.