Effect of various doses of recombinant human thyrotropin on the thyroid radioactive iodine uptake and serum levels of thyroid hormones and thyroglobulin in normal subjects

Recombinant human TSH (rhTSH), usually given as 0.9-mg doses im on 2 succes sive days, increases serum thyroglobulin (Tg) and radioactive iodine uptake (RAIU) in residual thyroid tissue in patients with thyroid cancer. We prev iously reported that a single, relatively low dose of rhTSH (0.1 mg im) is a potent stimulator of T-4, T-3, and Tg secretion in normal subjects. The p resent study describes the effects of higher doses of rhTSH on thyroid horm one and Tg secretion. Six normal subjects for each dose group, having no ev idence of thyroid disease, received either 0.3 or 0.9 mg rhTSH by im inject ion. Serum TSH, T-4, T-3, and Tg concentrations were measured at 2, 4, and 8 h and 1, 2, 3, 4, and 7 days after rhTSH administration. The peak serum T SH concentrations were 82 +/- 18 and 277 +/- 89 mU/L, respectively, for the 0.3- and 0.9-mg doses of rhTSH. Serum T-4, T-3, and Tg concentrations incr eased significantly in subjects receiving 0.3 and 0.9 mg rhTSH, with signif icant increases in T-4 and T-3 being observed before significant increases in serum Tg. Peak concentrations of serum T-4, T-3, and Tg, after 0.3 mg rh TSH administration, were 100 +/- 19, 131 +/- 14, and 1035 +/- 724% above in dividual baselines, respectively. Similarly, peak concentrations of serum T -4, T-3, and Tg, after 0.9 mg rhTSH administration, were 102 +/- 16, 134 +/ - 7, and 1890 +/- 768% above individual baselines, respectively. These data , compared with previously reported data for the responses to 0.1 mg rhTSH, indicated that 0.1, 0.3. and 0.9 mg rhTSH had similar quantitative stimula tory effects on thyroid hormone and Tg secretion, except that the T-4 respo nse was greater in groups receiving 0.3 and 0.9 mg rhTSH than in the group receiving 0.1 mg rhTSH. We also studied the effect of rhTSH on the thyroid RAIU in the group that received 0.9 mg rhTSH. The 6- and 24-h RAIU values w ere significantly higher after rhTSH (pre-rhTSH, 6-h value = 12.5 +/- 1.8%; 24 h value = 23 +/- 2.7%; post-rhTSH, 6 h value = 27 +/- 4.8%; 24-h value = 41 +/- 4.2%). The stimulating effects of 0.9 mg rhTSH on the 6- and 24-h RAIUs were similar, rhTSH is a potent stimulator of T-4, T-3, and Tg secret ion and the RAIU in normal subjects. Single doses greater than 0.1-0.3 mg d o not seem to further enhance thyroid hormone or Tg secretion.