Response to Orally Administered Synthetic Thyrotropin-Releasing Hormone in Man

Abstract
Serum TSH, T4, PB125I and thyroidal radioiodine uptake were measured in response to orally administered thyrotropin-releasing hormone (TRH). Doses of 1, 2 and 4 mg were given to 10 normal male subjects at 3–5-day intervals; 8 mg were given to 9 of the 10 subjects 3 days to 10 weeks following the 4 mg-dose. The serum TSH response to oral TRH was doserelated. The mean maximum increments ±sem in serum TSH produced by 1, 2, 4 and 8 mg were 0.7 ± 0.3, 1.7 ± 0.3, 2.9 ± 0.7 and 6.7 ± 1.0 μU/ml, respectively. The repetitive dosage schedule used in this study produced small, progressive increments in serum levels of T4 and increments in serum radioactive inorganic iodide, but clear increments in thyroidal radioiodine uptake and serum PB125I levels did not occur. No symptoms or toxic effects were observed. Oral administration of TRH will be a useful method of determining pituitary TSH reserve when the releasing factor is more readily available.

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