Alterations in circulating thyroid hormones and thyrotropin after complete thyroidectomy.

Changes in serum TSH, T4, T3, and rT3 concentrations after complete thyroidectomy were observed in 21 euthyroid patients with thyroid carcinoma. Serum TSH levels rose progressively during the 4 weeks of observation and a significant increase was noticed as early as 54 h after thyroidectomy. Serum T4 and T3 concentrations decreased significantly 42 and 6 h, respectively, after thyroidectomy. However, serum rT3 levels increased significantly within 18 h and reached maximum levels 30 h after thyroidectomy. The rates of decrease of serum T4 and T3 concentrations were constant between the 6–28 days after thyroidectomy (t)/2, 16.3 and 22.3 days, respectively), and the decrease rate of serum rT3 levels was similar to that of serum T4 after the day 18 (t1/2, 16.6 days). An initial sharp decrease in serum T3 and a sharp increase in serum rT3 concentrations without a significant change in serum T4 concentrations seems to be due to inhibition of outer ring monodeiodination in postsurgical states. When a significant ...