Kaptein E M, Hoopes M T, Parise M, Massry S G
Department of Medicine, University of Southern California, Los Angeles 90033.
Am J Physiol. 1991 Apr;260(4 Pt 1):E641-50. doi: 10.1152/ajpendo.1991.260.4.E641.
To evaluate reverse 3,3',5'-triiodothyronine (rT3) metabolism in nephrotic syndrome, serum rT3 kinetic studies from 10 nephrotics (mean urinary protein losses 7.0 g/day) with normal glomerular filtration rates (GFR; creatinine clearance 107 ml/min) were compared with 9 normal healthy subjects. Serum disappearance data were analyzed in a three-pool model, including rapidly (liver and kidney) and slowly (muscle, skin, and brain) equilibrating pools exchanging with serum, with all losses from the rapidly equilibrating pool. Serum free thyroxine (T4), determined by equilibrium dialysis, and parathyroid hormone levels were unaltered; total T4, T3, and rT3, and free rT3, albumin, and transferrin levels were significantly decreased; and free fractions of T4 and rT3 and thyroid-stimulating hormone (TSH) levels were increased. Despite reduced rT3 binding in serum, fractional transfer rates from serum to extravascular sites and serum clearance rates of total rT3 were unaltered. Free hormone clearance, serum appearance, and maximum hormone production rates were decreased. Total hormone transfer rates between serum and tissue pools and rT3 mass in serum and both tissue pools were reduced. Binding in the slowly equilibrating pool was decreased, and binding in both rapidly and slowly equilibrating pools was correlated with the free fraction of rT3 (r = -0.79, P = 0.007, and r = -0.70, P less than 0.025, respectively), with a shift of rT3 from the slow to the rapid pool. These findings suggest that binding of rT3 and T4 to serum carrier proteins is reduced, the transfer process for rT3 from serum to extravascular sites is decreased by factors in addition to reduced serum binding, degradation of rT3 is impaired, and decreased slow-pool binding may reflect reduced rT3 binding to serum-derived proteins in interstitial fluid. Furthermore, rT3 production rates are reduced, despite normal serum free T4 levels, accounting for low serum free rT3 concentrations. Total rT3 levels are decreased because of decrements in both serum binding and production rates.
为评估肾病综合征中反式3,3',5'-三碘甲状腺原氨酸（rT3）的代谢情况，对10例肾小球滤过率（GFR；肌酐清除率107 ml/分钟）正常的肾病患者（平均尿蛋白丢失7.0 g/天）的血清rT3动力学研究结果与9名正常健康受试者进行了比较。血清消失数据采用三室模型进行分析，该模型包括与血清进行交换的快速平衡室（肝脏和肾脏）和缓慢平衡室（肌肉、皮肤和大脑），所有损失均来自快速平衡室。通过平衡透析测定的血清游离甲状腺素（T4）和甲状旁腺激素水平未改变；总T4、T3和rT3以及游离rT3、白蛋白和转铁蛋白水平显著降低；T4和rT3的游离分数以及促甲状腺激素（TSH）水平升高。尽管血清中rT3结合减少，但从血清到血管外部位的分数转运率和总rT3的血清清除率未改变。游离激素清除率、血清出现率和最大激素产生率降低。血清与组织池之间的总激素转运率以及血清和两个组织池中的rT3质量均降低。缓慢平衡室中的结合减少，快速和缓慢平衡室中的结合均与rT3的游离分数相关（分别为r = -0.79，P = 0.007和r = -0.70，P < 0.025），rT3从缓慢平衡室向快速平衡室转移。这些发现表明，rT3和T4与血清载体蛋白的结合减少，除血清结合减少外，其他因素导致rT3从血清到血管外部位的转运过程减少，rT3的降解受损，缓慢平衡室结合减少可能反映rT3与组织间液中血清衍生蛋白的结合减少。此外，尽管血清游离T4水平正常，但rT3产生率降低，这导致血清游离rT3浓度较低。由于血清结合和产生率均下降，总rT3水平降低。
