Abstract
This study investigated the response of TSH secretion to 3,5,3′-triiodothyronine (T3) and 3,5,3′-triiodothyroacetic acid (Triac) in patients with resistance to thyroid hormone, and compared the responses with those in patients with TSH-secreting pituitary adenoma and normal subjects.
A short-term administration of 75 μg of T3 daily for 7 days suppressed serum TSH concentrations almost completely in normal subjects, but suppressed TSH only partially in patients with resistance to thyroid hormone and TSH-secreting pituitary adenoma. A single-dose administration of 75 μg of T3 gave similar results in regard to TSH suppressibility in these three subjects groups. In contrast, a single-dose administration of 1.4 mg of Triac remarkably suppressed serum TSH concentrations after 2 hours in not only normal subjects (-34 ± 11% [mean ± SD] from the basal value) but also in patients with resistance to thyroid hormone (-31 ± 9%), and this TSH suppression continued for 4 hours. After 24 hours, this TSH suppression persisted in normal subjects (-62 ± 12%) but was relieved in patients with resistance to thyroid hormone (-23 ± 14%). After the Triac administration, molar ratios of α-subunit to TSH in serum were decreased in patients with TSH-secreting pituitary adenoma but increased in patients with resistance to thyroid hormone.
Because the Triac therapy for patients with resistance to thyroid hormone suppressed pituitary-TSH secretion during the early phase of drug ingestion, this drug should be given several times within a day to obtain continuous TSH-suppressive effects.
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