Thyroid Autoimmune Disease Unit, Cedars-Sinai Research Institute and UCLA School of Medicine, 8700 Beverly Blvd., Los Angeles, CA 90048, USA.
Thyroid. 2010 Oct;20(10):1157-62. doi: 10.1089/thy.2010.0117.
Recombinant-inbred mouse strains differ in their susceptibility to Graves'-like hyperthyroidism induced by immunization with adenovirus expressing the human thyrotropin (TSH) receptor. Because one genetic component contributing to this susceptibility is altered thyroid sensitivity to TSH receptor agonist stimulation, we wished to quantify thyroid responsiveness to TSH. For such studies, it is necessary to suppress endogenous TSH by administering L-3,5,3′-triiodothyronine (L-T3), with the subsequent decrease in serum thyroxine (T4) reflecting endogenous TSH suppression. Our two objectives were to assess in different inbred strains of mice (i) the extent of serum T4 suppression after L-T3 administration and (ii) the magnitude of serum T4 increase induced by TSH.
Mice were tail-bled to establish baseline-serum T4 before L-T3 administration. We initially employed a protocol of L-T3-supplemented drinking water for 7 days. In subsequent experiments, we injected L-T3 intraperitoneally (i.p.) daily for 3 days. Mice were then injected i.p. with bovine TSH (10 mU) and euthanized 5 hours later. Serum T4 was assayed before L-T3 administration, and before and after TSH injection. In some experiments, serum T3 and estradiol were measured in pooled sera.
Oral L-T3 (3 or 5 µg/mL) suppressed serum T4 levels by 26%-64% in female BALB/c mice but >95% in males. T4 suppression in female B6 mice ranged from 0% to 90%. In C3H mice, L-T3 at 3 µg/mL was ineffective but 5 µg/mL achieved >80% serum T4 reduction. Unlike inbred mice, in outbred CF1 mice the same protocol was more effective: 83% in females and 100% suppression in males. The degree of T4 suppression was unrelated to baseline T4, T3, or estradiol, but was related to mouse weight and postmortem T3, with greater suppression in larger mice (outbred CF1 animals and inbred males). Among females with serum T4 suppression >80%, the increase in serum T4 after TSH injection was greater for BALB/c and C3H versus B6 mice. Moreover, the T4 increment was higher in female than in male BALB/c.
Our data provide important, practical information for future in vivo studies in inbred mice: we recommend that responses to TSH be performed in female animals injected with L-T3 i.p. to suppress baseline T4.
通过腺病毒表达人促甲状腺激素（TSH）受体免疫，重组近交系小鼠在 Graves 样甲状腺功能亢进症的易感性上存在差异。由于导致这种易感性的一个遗传成分是甲状腺对 TSH 受体激动剂刺激的敏感性改变，我们希望量化甲状腺对 TSH 的反应性。对于这样的研究，有必要通过给予 L-3,5,3′-三碘甲状腺原氨酸（L-T3）来抑制内源性 TSH，随后血清甲状腺素（T4）的下降反映了内源性 TSH 的抑制。我们的两个目标是评估不同近交系小鼠（i）给予 L-T3 后血清 T4 的抑制程度，（ii）TSH 诱导的血清 T4 增加的幅度。
小鼠尾采血以建立给予 L-T3 前的基础血清 T4。我们最初采用了 7 天补充 L-T3 饮用水的方案。在随后的实验中，我们每天腹腔内（i.p.）注射 L-T3 3 天。然后，小鼠被腹腔注射牛 TSH（10 mU），并在 5 小时后安乐死。在给予 L-T3 之前、之后以及 TSH 注射之前测定血清 T4。在一些实验中，在混合血清中测量血清 T3 和雌二醇。
口服 L-T3（3 或 5 µg/mL）在雌性 BALB/c 小鼠中抑制血清 T4 水平 26%-64%，但在雄性中抑制 >95%。B6 雌性小鼠的 T4 抑制范围为 0%-90%。在 C3H 小鼠中，3 µg/mL 的 L-T3 无效，但 5 µg/mL 实现 >80%的血清 T4 减少。与近交系小鼠不同，在外系 CF1 小鼠中，相同的方案更有效：雌性 83%，雄性 100%抑制。T4 抑制的程度与基线 T4、T3 或雌二醇无关，但与小鼠体重和死后 T3 有关，较大的小鼠（外系 CF1 动物和近交系雄性）抑制更大。在血清 T4 抑制 >80%的雌性中，给予 L-T3 抑制基础 T4 后，TSH 注射后血清 T4 的增加在 BALB/c 和 C3H 与 B6 小鼠之间更大。此外，在雌性 BALB/c 中，T4 增加量高于雄性。
我们的数据为未来近交系小鼠体内研究提供了重要的实用信息：我们建议使用腹腔内注射 L-T3 抑制基础 T4 的雌性动物来进行 TSH 反应的检测。
