Bianchi R, Mariani G, Molea N, Vitek F, Cazzuola F, Carpi A, Mazzuca N, Toni M G
J Clin Endocrinol Metab. 1983 Jun;56(6):1152-63. doi: 10.1210/jcem-56-6-1152.
We describe here a new method for the direct measurement of the conversion rate of T4 to T3 in man. The metabolic study was performed in 23 subjects: 13 healthy controls, 7 T4-treated hypothyroids, and 3 sick euthyroid patients. The experimental protocol involved the simultaneous iv bolus injection of [125I]T4 and [131I]T3, and the use of Sephadex G-25 column chromatography to determine the plasma concentrations of [125I]T4, [131I]T3, and [125I]T3 newly formed through 5'-monodeiodination of labeled T4 in the peripheral tissues. The T4 and T3 kinetic parameters were determined by noncompartmental analysis. The conversion rate of T4 to T3 was computed by a method based on the precursor-product relationship, using the [131I]T3 disappearance curve for correcting the concentrations of newly formed [125I]T3 (convolution method). The conversion rate of T4 to T3 was 0.2541 +/- 0.0125 (mean +/- SEM) in the control group and was significantly reduced (0.1283 +/- 0.0204; P less than 0.001) in the sick euthyroid patients, while it was slightly, though not significantly, increased in the T4-treated patients (0.2932 +/- 0.0220). A close agreement was found between the values for the conversion rate obtained by the convolution approach and those derived from the ratio between the serum concentrations of [125I]T3 and [125I]T4 at equilibrium. The conversion rates obtained by the convolution approach were also in good agreement with the values estimated from the molar ratio between the turnover rates of T3 and T4. In the control group, 72.0 +/- 3.6% of the circulating T3 was produced by 5'-monodeiodination of T4 in the peripheral tissues, and 28.0 +/- 3.6% of the circulating T3 derived from direct thyroidal secretion. The sick euthyroid patients showed a significantly smaller proportion of circulating T3 deriving from peripheral conversion of T4 (52.5 +/- 3.9%; P less than 0.025).
我们在此描述一种直接测量人体中T4向T3转化率的新方法。对23名受试者进行了代谢研究：13名健康对照者、7名接受T4治疗的甲状腺功能减退患者和3名甲状腺功能正常的患病患者。实验方案包括同时静脉推注[125I]T4和[131I]T3，并使用葡聚糖G - 25柱色谱法测定血浆中[125I]T4、[131I]T3以及通过外周组织中标记T4的5'-单脱碘作用新形成的[125I]T3的浓度。通过非房室分析确定T4和T3的动力学参数。T4向T3的转化率通过基于前体 - 产物关系的方法计算，使用[131I]T3消失曲线校正新形成的[125I]T3的浓度（卷积法）。对照组中T4向T3的转化率为0.2541±0.0125（平均值±标准误），在甲状腺功能正常的患病患者中显著降低（0.1283±0.0204；P＜0.001），而在接受T4治疗的患者中虽有轻微但不显著的升高（0.2932±0.0220）。发现通过卷积法获得的转化率值与平衡时血清中[125I]T3和[125I]T4浓度之比得出的转化率值之间密切一致。通过卷积法获得的转化率也与根据T3和T4周转率的摩尔比估算的值高度一致。在对照组中，72.0±3.6%的循环T3由外周组织中T4的5'-单脱碘作用产生，28.0±3.6%的循环T3来自甲状腺直接分泌。甲状腺功能正常的患病患者中，来自T4外周转化的循环T3比例显著较小（52.5±3.9%；P＜0.025）。
