Gardner D F, Kaplan M M, Stanley C A, Utiger R D
N Engl J Med. 1979 Mar 15;300(11):579-84. doi: 10.1056/NEJM197903153001102.
To determine the implication of decreased T3 production during fasting, seven normal men were fasted for 80 hours on two occasions; they received 5 microgram of T3 every three hours durnig the second fast. The mean serum T3 concentration declined during the control fast from 120 to 73 ng per deciliter (P less than 0.01), but remained slightly above base-line values during the T3 fast. Mean serum T4 concentrations did not change, and mean serum rT3 concentrations increased, during both fasts. The peak serum TSH increment after TRH was 11.1 micromicron per milliliter before fasting, 8.9 (not significant) after the control fast and 2.2 (P less than 0.01) after the T3 fast. Urea excretion was 9.1 per cent higher during the T3 fast; there were no differences in the changes in blood glucose, plasma fatty acids or other substrates during the two fasts. Pretreatment with potassium iodide lowered serum T4 concentrations and increased the serum TSH response to TRH after fasting. We conclude that the decrease in serum T3 concentrations during fasting spares muscle protein. Fasting is accompanied by a lower set point of TSH secretion, which remains sensitive to changes in serum thyroid hormone concentrations.
为了确定禁食期间三碘甲状腺原氨酸（T3）生成减少的影响，七名正常男性分两次禁食80小时；在第二次禁食期间，他们每三小时接受5微克的T3。在对照禁食期间，血清T3平均浓度从每分升120纳克降至73纳克（P<0.01），但在T3禁食期间仍略高于基线值。在两次禁食期间，血清T4平均浓度均未改变，血清反T3（rT3）平均浓度均升高。促甲状腺激素释放激素（TRH）刺激后血清促甲状腺激素（TSH）的峰值增量在禁食前为每毫升11.1微单位，对照禁食后为8.9（无显著差异），T3禁食后为2.2（P<0.01）。在T3禁食期间尿素排泄量高9.1%；两次禁食期间血糖、血浆脂肪酸或其他底物的变化无差异。禁食前用碘化钾预处理可降低血清T4浓度，并增加禁食后血清TSH对TRH的反应。我们得出结论，禁食期间血清T3浓度的降低可节省肌肉蛋白质。禁食伴随着较低的TSH分泌设定点，该设定点对血清甲状腺激素浓度的变化仍保持敏感。
