Keck F S, Loos U
Medizinische Klinik und Poliklinik, Abteilung Innere Medizin I, Universität Ulm, Germany.
Horm Metab Res. 1988 Feb;20(2):110-4. doi: 10.1055/s-2007-1010765.
This study describes an extrathyroidal mechanism for regulating serum concentration of triiodothyronine (T3) in thyroxine (T4) deficiency or excess. Serum levels of T3, T4, reverse T3 (rT3), and thyrotropin were determined in two series of athyreotic patients (n = 22 and n = 16, respectively) during various doses of T4 substitution therapy. The patients were followed from the severe hypothyroid state up to the modest hyperthyroid state, induced by stepwise increasing doses of administered T4. The periods of constant T4 replacement doses were 1 week (group I) and 5 weeks (group II), respectively. As serum T4 levels rose from less than 0.5 micrograms/dl to 18.9 micrograms/dl, serum T3 levels showed a curvilinear increase, which was pronounced in the very low T4 range while it was flattened at the higher end of the spectrum of T4 levels. As to rT3, an analogous course did not occur. The different character of the relationships between T4 and its conversion products was further elucidated by calculating the T3/T4 and rT3/T4 ratios. T3/T4 ratio declined fourfold from 43.3.10(-3) in the severe hypothyroid to 11.7.10(-3) in the hyperthyroid range. The results support the hypothesis of a peripheral autoregulation of T4 to T3 conversion which appears to be operative at both ends of the T4 spectrum and which serves to maintain or defend serum T3 levels.
本研究描述了一种甲状腺外机制，用于在甲状腺素（T4）缺乏或过量时调节血清三碘甲状腺原氨酸（T3）浓度。在两组甲状腺切除患者（分别为n = 22和n = 16）接受不同剂量T4替代治疗期间，测定了血清T3、T4、反三碘甲状腺原氨酸（rT3）和促甲状腺激素水平。患者从严重甲状腺功能减退状态开始，随着T4给药剂量逐步增加，直至进入轻度甲状腺功能亢进状态。T4持续替代剂量的周期分别为1周（I组）和5周（II组）。随着血清T4水平从低于0.5微克/分升降至18.9微克/分升，血清T3水平呈曲线上升，在极低T4范围内上升明显，而在T4水平范围较高端趋于平缓。至于rT3，未出现类似变化过程。通过计算T3/T4和rT3/T4比值，进一步阐明了T4与其转化产物之间关系的不同特征。T3/T4比值从严重甲状腺功能减退时的43.3×10⁻³降至甲状腺功能亢进范围内的11.7×10⁻³，下降了四倍。这些结果支持了T4向T3转化的外周自动调节假说，该调节似乎在T4水平范围的两端均起作用，并有助于维持或保护血清T3水平。
