Effects of oral thyrotropin-releasing hormone, exogenous thyroid-stimulating hormone, and withdrawal of triiodothyronine on 131I uptake after subtotal thyroidectomy.

Abstract

To characterize the effects of oral TRH, exogenous TSH, and length of time of T3 withdrawal on I3II uptake, 16 patients who had undergone subtotal thyroidectomy for differentiated thyroid cancer were administered T3 (75-100 μg/day) for 8–15 weeks before 131I remnant ablation. T3 was withdrawn for 10 days in 8 patients (group 1) and for 24 days in 8 patients (group 2) before a baseline 24-h 131I uptake (study day 2), with repeat uptakes (study days 5 and 7) after the sequential administration of oral TRH (80 mg 3 times a day for 3 days) and after bovine TSH (10 U im each day for 2 days). Baseline serum TSH values were 30 ± 8 μU/ml in group 1 and 73 ± 14 in group 2 (P < 0.02), and the values did not increase at the end of the study (day 7; 36 ± 9 and 77 ± 12, respectively). Four hours after doses 1 and 7 of oral TRH, changes in serum TSH values were 10 ± 4 and 9 ± 2 in group 1, respectively, and 17 ± 6 and 10 ± 3 in group 2, respectively. The 131I uptake increased 2.8 ± 0.7% after oral TRH in group 1 (an in...