Shulkin B L, Utiger R D
J Clin Endocrinol Metab. 1984 Jun;58(6):1184-7. doi: 10.1210/jcem-58-6-1184.
Serum rT3 concentrations are often increased in patients with nonthyroid illness. Such elevations could be responsible for some of the alterations in pituitary-thyroid function that occur in such patients, particularly since rT3 is a potent inhibitor of extrathyroidal T3 production in vitro. To evaluate the role of serum rT3 elevations in the regulation of the hypothalamic-pituitary-thyroid axis, 10 normal subjects were given 3 mg rT3, orally, in divided doses for 4 days. Serum rT3 concentrations were elevated at least 10-fold by the end of the first day of treatment. Mean serum T4 and T3 concentrations did not change, nor was there any change in basal or TRH-stimulated serum TSH concentrations. There was, likewise, no change in serum binding of T3 or T4. These results show that rT3, given orally, has no detectable activity in normal subjects, and hence, elevations in serum rT3 concentrations per se do not contribute to other abnormalities in thyroid function found in patients with nonthyroid illness.
非甲状腺疾病患者的血清反三碘甲状腺原氨酸（rT3）浓度常升高。这种升高可能是此类患者垂体 - 甲状腺功能出现某些改变的原因，特别是因为rT3在体外是甲状腺外三碘甲状腺原氨酸（T3）生成的强效抑制剂。为了评估血清rT3升高在下丘脑 - 垂体 - 甲状腺轴调节中的作用，10名正常受试者口服3mg rT3，分剂量服用4天。治疗第一天结束时，血清rT3浓度至少升高了10倍。血清T4和T3的平均浓度没有变化，基础或促甲状腺激素释放激素（TRH）刺激的血清促甲状腺激素（TSH）浓度也没有变化。同样，T3或T4的血清结合也没有变化。这些结果表明，口服rT3在正常受试者中没有可检测到的活性，因此，血清rT3浓度本身的升高并不会导致非甲状腺疾病患者出现其他甲状腺功能异常。
