Gavin L A, Moeller M, McMahon F A, Castle J N, Gulli R, Cavalieri R R
Department of Medicine, Veterans' Administration Medical Center, San Francisco, California 94121.
Endocrinology. 1988 Aug;123(2):1075-81. doi: 10.1210/endo-123-2-1075.
The glucose-fed rat, in contrast to the chow-fed animal, has a higher serum total T3 concentration and an increase in the hepatic content of T4 5'-deiodinase (type I) activity. The mechanism and significance of these glucose-induced changes in T3 metabolism are elucidated in this study. To focus on extrathyroidal thyroid hormone metabolism the kinetic parameters were determined in thyroidectomized T4-replaced rats (1.25 micrograms T4/100 g BW.day). Kinetics of T4 and T3 were studied separately by infusing labeled hormone to equilibrium. Glucose feeding for 72 h (G) significantly increased both the total and free serum T3 concentrations compared to the respective means in the chow-fed control group (P). The glucose-induced changes in serum T3 reflect the approximate doubling of T3 production to 14.7 +/- 0.6 ng/h.100 g in G rats compared to 7.6 +/- 0.7 ng/h.100 g in P rats. The higher T3 production rate in the G group is due to a significant increase in the fractional total body T4 to T3 conversion (0.33 +/- 0.02) compared to that in the P group (0.19 +/- 0.02). The tissue (liver, kidney, brain, and brown adipose tissue) concentration of T4 (nanograms per g wet wt) was significantly increased in the G group. The increase ranged from 54% in liver to 80% in kidney, brain, and brown adipose tissue. The tissue concentration of T3 (nanograms per g wet wt) was even more dramatically increased by glucose feeding than was T4. The glucose-induced increment in organ T3 ranged from 2.5-fold (kidney, muscle, and brain) to 5-fold (liver and white adipose tissue) to 12-fold (brown adipose tissue). These data indicate that the increase in serum total and free T3 concentrations associated with glucose feeding reflects augmented total body T3 production from T4. The effect of the enhanced T3 neogenesis was generalized, as the T3 content was increased in each organ studied. Thus, glucose feeding has unique effects on T3 metabolism.
与喂食普通饲料的动物相比，喂食葡萄糖的大鼠血清总T3浓度更高，肝脏中T4 5'-脱碘酶（I型）活性的含量增加。本研究阐明了这些由葡萄糖引起的T3代谢变化的机制和意义。为了聚焦于甲状腺外甲状腺激素代谢，在甲状腺切除并用T4替代的大鼠（1.25微克T4/100克体重·天）中测定动力学参数。通过输注标记激素至平衡状态分别研究T4和T3的动力学。与喂食普通饲料的对照组（P）各自的均值相比，喂食葡萄糖72小时（G）显著增加了血清总T3和游离T3浓度。葡萄糖诱导的血清T3变化反映出T3生成量大约翻倍，G组大鼠为14.7±0.6纳克/小时·100克，而P组大鼠为7.6±0.7纳克/小时·100克。G组较高的T3生成率是由于全身T4向T3转化分数显著增加（0.33±0.02），相比之下P组为（0.19±0.02）。G组中组织（肝脏、肾脏、大脑和棕色脂肪组织）的T4浓度（每克湿重纳克数）显著增加。增加幅度从肝脏的54%到肾脏、大脑和棕色脂肪组织的80%不等。与T4相比，喂食葡萄糖使组织中T3浓度（每克湿重纳克数）增加得更为显著。葡萄糖诱导的器官T3增加幅度从2.5倍（肾脏、肌肉和大脑）到5倍（肝脏和白色脂肪组织）再到12倍（棕色脂肪组织）。这些数据表明，与喂食葡萄糖相关的血清总T3和游离T3浓度增加反映了全身从T4生成T3的增加。增强的T3新生作用具有普遍性，因为在所研究的每个器官中T3含量都增加了。因此，喂食葡萄糖对T3代谢具有独特的影响。
