Edwards B R, Stern P, Stitzer L K, Galton V A
Acta Endocrinol (Copenh). 1976 Aug;82(4):737-45. doi: 10.1530/acta.0.0820737.
Other investigators have reported that whole body clearance of thyroxine (T4) is increased in hyperthyroid rats isotopically equilibrated with radioactive T4, using the 24 h post-injection serum T4 concentration in the clearance calculation. Data from this laboratory indicate that serum T4 concentration is lowest at this point yielding falsely high clearance values, particularly when high doses of T4 are injected. To investigate this problem further, two types of experiments were performed. First, rats were equilibrated with [125I]T4, 5 or 20 mug/day, and the urinary clearance of iodide derived from T4 (deiodinative clearance) was measured from 0-7 and 7-24 h after a T4 injection, using the T4 concentration in serum obtained at the midpoint of each urine collection period. Urine was then collected from the ureters for several 1 h periods during the 4th to 8th h following T4 injection, calculating clearances using the midpoint plasma T4 concentration. Second, normal rats were given a single dose of [125I]T4, 5 or 55 mug/rat, and deiodinative clearance was determined during the subsequent 0-7 and 7-24 h periods. The first experiment indicated that deiodinative clearance was significantly enhanced in rats equilibrated with the large dose of T4 under all conditions studied. In contrast, the clearance in normal rats given a single large dose of T4 was not significantly different from that of normal rats given a small dose of T4. These results support the view that T4 clearance is increased in hyperthyroidism, due in part to an increase in the deiodination of T4.
其他研究人员报告称，在与放射性甲状腺素（T4）进行同位素平衡的甲状腺功能亢进大鼠中，使用注射后24小时血清T4浓度进行清除率计算时，T4的全身清除率会增加。本实验室的数据表明，此时血清T4浓度最低，会得出错误的高清除率值，尤其是在注射高剂量T4时。为了进一步研究这个问题，进行了两种类型的实验。首先，用5或20μg/天的[125I]T4使大鼠达到平衡，并在注射T4后0至7小时和7至24小时测量源自T4的碘化物的尿清除率（脱碘清除率），使用每个尿液收集期中点获得的血清中T4浓度。然后在注射T4后的第4至8小时内，从输尿管收集尿液数小时，使用血浆T4浓度中点计算清除率。其次，给正常大鼠单次注射5或55μg/只的[125I]T4，并在随后的0至7小时和7至24小时内测定脱碘清除率。第一个实验表明，在所有研究条件下，用大剂量T4平衡的大鼠的脱碘清除率显著提高。相比之下，单次给予大剂量T4的正常大鼠的清除率与给予小剂量T4的正常大鼠的清除率没有显著差异。这些结果支持了这样一种观点，即甲状腺功能亢进时T4清除率增加，部分原因是T4脱碘增加。
