TOLERANCE OF NORMAL, OF THYROIDECTOMIZED, AND OF THIOUREA OR THIOURACIL TREATED DOGS TO ORAL DESICCATED THYROID AND TO INTRAVENOUS THYROXINE1

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Abstract
HUMAN PATIENTS with myxedema can not take oral desiccated thyroid in amounts greater than about 0.2 gram daily without developing a supranormal level of precipitable iodine in serum along with symptoms and signs of hyperthyroidism (Winkler, Criscuolo and Lavietes, 1943; Winkler, Riggs and Man, 1945). Tolerance never develops. Euthyroid subjects, on the other hand, can often tolerate indefinitely much larger amounts of desiccated thyroid, 0.3 to 0.9 gram daily, before metabolic rate and precipitable iodine of serum increase (Riggs, Man and Winkler, 1945; Peters, Danowski and Winkler). The ingested hormone is apparently not stored by euthyroid subjects, since there is no evidence of its eventual release when thyroid medication is discontinued. A difference in response to intravenous thyrosine between myxedematous patients and euthyroid subjects has also been noted (Means, 1937; Winkler, Lavietes, Robbins and Man, 1943). As far as is known the myxedematous subject adequately treated with thyroid medication differs from the euthyroid subject only in having no thyroid tissue (Means, 1937).