LoPresti J S, Warren D W, Kaptein E M, Croxson M S, Nicoloff J T
J Clin Endocrinol Metab. 1982 Oct;55(4):666-70. doi: 10.1210/jcem-55-4-666.
A new method is described for the estimation of T4 to T3 conversion in man and is applied to the study of hyperthyroid and hypothyroid clinical states. The method employs simultaneous iv injection of [125I]T4 and [131I]T3 with isolation of the labeled T3 tracers in 4- to 8-day pooled urine samples by a combination of solvent extraction, desalting, and immunoprecipitation procedures. Using [131I]T3 as a recovery standard, the T4 to T3 conversion ratio was found to be 0.470 +/- 0.011 in euthyroid subjects. This confirmed our earlier findings of 0.482 +/- 0.014 using a paper chromatographic method and nonsimultaneous isotope administration. The conversion ratio was increased in hypothyroidism to 0.535 +/- 0.011 (P less than 0.02) and decreased in hyperthyroidism to 0.415 +/- 0.009 (P less than 0.01). These changes parallel the fraction of the radioiodine collected in the urine for both T4 and T3; normal values are 77 +/- 4% for T4 and 76 +/- 4% for T3, values in hypothyroidism are 79 +/- 1% for T4 and 79 +/- 3% for T3, and values in hyperthyroidism are 58 +/- 3% for T4 and 58 +/- 5% for T3 (P less than 0.01). These findings indicate that 1) urinary T4 to T3 conversion values are highly reproducible in euthyroid as well as hyperthyroid and hypothyroid states; 2) the reduction in T4 to T3 conversion in hyperthyroidism probably reflects increased T4 disposal by nondeiodinative pathways and possibly the reverse in hypothyroid states; and 3) since urinary T4 to T3 conversion values in euthyroid subjects exceeded all reported conversion values in blood, there may be an alternate pathway of T3 production and disposal which is not reflected in the blood T3 production rate.
本文描述了一种估算人体中 T4 向 T3 转化的新方法，并将其应用于甲状腺功能亢进和甲状腺功能减退临床状态的研究。该方法采用同时静脉注射[125I]T4 和[131I]T3，并通过溶剂萃取、脱盐和免疫沉淀程序的组合，在 4 至 8 天的混合尿液样本中分离标记的 T3 示踪剂。以[131I]T3 作为回收标准，发现甲状腺功能正常的受试者中 T4 向 T3 的转化比率为 0.470±0.011。这证实了我们早期使用纸色谱法和非同时同位素给药时得到的 0.482±0.014 的结果。甲状腺功能减退时转化比率增加至 0.535±0.011（P＜0.02），甲状腺功能亢进时降低至 0.415±0.009（P＜0.01）。这些变化与 T4 和 T3 在尿液中收集的放射性碘分数平行；T4 的正常值为 77±4%，T3 为 76±4%，甲状腺功能减退时 T4 为 79±1%，T3 为 79±3%，甲状腺功能亢进时 T4 为 58±3%，T3 为 58±5%（P＜0.01）。这些发现表明：1）甲状腺功能正常以及甲状腺功能亢进和减退状态下，尿液中 T4 向 T3 的转化值具有高度可重复性；2）甲状腺功能亢进时 T4 向 T3 转化的降低可能反映了通过非脱碘途径增加的 T4 处置，甲状腺功能减退状态下可能相反；3）由于甲状腺功能正常的受试者尿液中 T4 向 T3 的转化值超过了所有报道的血液中的转化值，可能存在一条 T3 产生和处置的替代途径，而这在血液 T3 产生率中未得到体现。
