A DETERMINATION OF THE RATE OF THYROID HORMONE SECRETION AT VARIOUS ENVIRONMENTAL TEMPERATURES1

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Abstract
The maintenance or restoration of normal thyroid wt. by the adm. of thyroxin to rats simultaneously treated with the anti-thyroid drug thiouracil was used as the basis of an assay procedure for thyroid hormone. The rate of thyroid enlargement in response to thiouracil administration was low in hot environments and high in cold. A quantity of thyroid hormone equivalent to 5.2 [mu]g. thyroxin daily was required to maintain a normal thyroid in young [female] rats kept at room temps. averaging 25[degree]C. At 1[degree]C, the thyroxin requirement was increased to 9.5 [mu]g., while at 35[degree]C. it was decreased to 1.7 [mu]g. These values are considered to be quantitatively equivalent to the amt. of hormone produced by the normal thyroid gland under these conditions.