Alterations in thyroid blood flow induced by varying levels of iodine intake in the rat.
Alterations in thyroid blood flow induced by varying levels of iodine intake in the rat.
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DOI：
10.1210/endo-125-1-54
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发表时间：
1989-07
期刊：
影响因子：
4.8
通讯作者：
M. Michalkiewicz;L. Huffman;J. M. Connors;G. Hedge
中科院分区：
文献类型：
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作者：
M. Michalkiewicz;L. Huffman;J. M. Connors;G. Hedge
甲状腺激素的生物合成依赖于适量的甲状腺碘的存在，在饮食碘摄入量的波动期间，各种体内平衡机制维持相对稳定的甲状腺激素水平。这些机制包括在碘摄入量有限时提高碘泵效率和有机化，以及当碘摄入量过高时碘摄取和激素合成显著减少。本研究旨在确定适应不同的饮食碘方案是否与甲状腺血流量的变化有关，并评估任何此类变化与垂体-甲状腺轴激素水平相关的时间进程。雄性SD大鼠喂饲低碘(LID)、高碘(HID)或正常碘(CTR)的饲料。在开始这些饮食方案的3天、7天、14天或133天后，用氯胺酮/戊巴比妥钠麻醉动物，并使用参考样本版本的微球技术评估甲状腺血流量。在133天的治疗过程中，在相同的时间和每周一次的间隔中，采集血液样本以测定TSH、T4和T3水平。实验结束时测定甲状腺免疫活性血管活性肠肽(VIP)。在治疗7、14和133天时，LID治疗使甲状腺血流量分别增加到对照组的240%、350%和240%。在这些时间段，对照组动物的甲状腺重量也高于正常水平。在LID治疗的133天中，血浆T4水平略有下降；然而，这种饮食方案并没有改变循环中的T3或TSH水平或甲状腺VIP浓度。一般来说，HID治疗的效果与LID相反。HID治疗3、7、14和133天后，甲状腺血流量分别减少34%、56%、46%和35%。在HID治疗的133天中，循环中的T4水平升高，而血浆中的T3和TSH水平以及甲状腺重量在此研究期间与对照组相比保持不变。在HID治疗开始时，观察到甲状腺VIP浓度的轻微下降与甲状腺血流量的下降相一致。LID和HID对血压、心输出量或其他器官的血流量均无影响。这些数据表明，大鼠对饮食碘摄入量变化的适应包括甲状腺血流量的变化，这些变化与碘摄入量水平成反比，似乎与循环TSH水平无关。
Thyroid hormone biosynthesis depends upon the presence of adequate amounts of thyroidal iodine, and during fluctuations in dietary iodine intake, relatively constant thyroid hormone levels are maintained by various homeostatic mechanisms. These mechanisms include an enhancement of iodide pump efficiency and organification when iodine intake is limited, and significant decreases in iodide uptake and hormone synthesis when excess iodine intake occurs. The present study was designed to determine whether acclimation to different dietary iodine regimens is associated with changes in thyroid blood flow and to assess the time course of any such alterations in relation to pituitary-thyroid axis hormone levels. Male Sprague-Dawley rats were fed a diet containing low (LID), high (HID), or normal (CTR) iodine concentrations. Three, 7, 14, or 133 days after starting these dietary regimens, the animals were anesthetized with ketamine/pentobarbital, and thyroid blood flows were assessed using the reference sample version of the microsphere technique. At the same times and at weekly intervals throughout the 133 days of treatment, blood samples for the determination of TSH, T4, and T3 levels were obtained. Additionally, thyroidal immunoreactive vasoactive intestinal peptide (VIP) was measured at the end of the experiments. LID treatment increased thyroid blood flows to 240%, 350%, and 240% of levels in control rats at 7, 14, and 133 days of treatment, respectively. Thyroid weight was also elevated above levels in control animals at each of these times. A slight decrease in plasma T4 levels occurred over the 133 days of LID treatment; however, this dietary regimen did not alter circulating levels of T3 or TSH or thyroidal VIP concentration. HID treatment had opposite effects, in general, to those of LID. Thyroid blood flows were decreased by 34%, 56%, 46%, and 35% after 3, 7, 14, and 133 days of treatment with HID, respectively. Circulating levels of T4 were increased over the 133 days of HID treatment, whereas plasma levels of T3 and TSH and thyroid weights remained unchanged from those in control rats over this period of study. A small decrease in thyroidal VIP concentrations coincident with the decrease in thyroid blood flow was observed at the beginning of the HID treatment. Neither LID nor HID had any effect on blood pressure, cardiac output, or blood flow in other organs. These data demonstrate that acclimation to changes in dietary iodine intake in the rat include alterations in thyroid blood flow which are reciprocal to the iodine intake level and appear to be independent of circulating TSH levels.