Brain cortex reverse triiodothyronine (rT3) and triiodothyronine concentrations under steady state infusions of thyroxine and rT3.
Brain cortex reverse triiodothyronine (rT3) and triiodothyronine concentrations under steady state infusions of thyroxine and rT3.
复制标题
甲状腺素和 rT3 稳态输注下，脑皮层逆转三碘甲状腺原氨酸 (rT3) 和三碘甲状腺原氨酸浓度。
作者：
M. Goumaz;C. Kaiser;A. Burger
T4和反向T3（rT3）可以抑制大鼠大脑皮层、垂体和棕色脂肪组织中的5'-脱碘酶II型活性，增加了T4转化为rT3后在体内发挥作用的可能性。本研究的目的是测量甲状腺功能减退 (Tx) 大鼠在连续 7 天持续输注 [125I]T4（相当于 12 pmol T4/天 X 100 g 体重 (BW)）或与 400 pmol T4/天一起输注期间脑皮质 rT3 的含量。结合Sephadex G-25吸附色谱、HPLC和免疫沉淀从脑皮质、垂体、肾脏和肝脏中提取[125I]T4、rT3和T3。 [131I]T4、T3或rT3用作内标。在输注 [125I]T4（12 pmol T4/天 X 100 g BW）的 Tx 大鼠和输注 400 pmol T4/天 X 100 g BW 的 Tx 大鼠中，可在脑皮层、肝脏和肾脏中检测到 [125I]rT3。 rT3 浓度最高出现在大脑皮层，占局部 T4 浓度的 6% 至 10.5%。在输注400 pmol T4/天×100 g BW期间，脑皮质中T3浓度比血清中高6倍，甚至超过T4。在单独接受[125I]T4的Tx大鼠中，脑皮质与血清T3的比率为3:1，但通过RIA测量的总血清T3浓度远高于由于转换而产生的浓度[0.50 +/- (SE) 0.1 pmol/ml vs. 0.018 +/- 0.002 pmol T3/ml]，表明甲状腺分泌。通过输注[125I]rT3 4 天来测量血脑屏障对rT3 的影响。杀死后，如上分离rT3。大约 3% 的血清 rT3 是从大脑皮质中回收的，而在 T4 输注过程中，发现了 40-50% 的血清 rT3，这表明 rT3 是大脑皮质局部产生的。
T4 and reverse T3 (rT3) can inhibit 5'-deiodinase type II activity in rat brain cortex, pituitary, and brown adipose tissue, raising the possibility that T4 may act in vivo after conversion to rT3. The aim of this study was to measure in hypothyroid (Tx) rats the content of brain cortex rT3 during a constant 7-day infusion of either [125I]T4 alone, corresponding to 12 pmol T4/day X 100 g body weight (BW), or together with 400 pmol T4/day. [125I]T4, rT3, and T3 were extracted from brain cortex, pituitary, kidney, and liver with a combination of adsorption chromatography on Sephadex G-25, HPLC, and immunoprecipitation. [131I]T4, T3, or rT3 were used as internal standards. [125I]rT3 could be detected in brain cortex, liver, and kidney in Tx rats infused with [125I]T4 (12 pmol T4/day X 100 g BW) and in those infused with 400 pmol T4/day X 100 g BW. The highest rT3 concentrations were found in brain cortex, where it represented 6% to 10.5% of the local T4 concentration. During an infusion of 400 pmol T4/day X 100 g BW, brain cortex T3 concentration was 6 times higher in the brain cortex than in serum, and even exceeded that of T4. In Tx rats receiving [125I]T4 alone the brain cortex to serum T3 ratio was 3:1, but the total serum T3 concentration, measured by RIA, was much higher than that due to conversion [0.50 +/- (SE) 0.1 pmol/ml vs. 0.018 +/- 0.002 pmol T3/ml], indicating thyroidal secretion. The effect of the blood-brain barrier on rT3 was measured by infusing [125I]rT3 over 4 days. After killing, rT3 was isolated as above. Approximately 3% of serum rT3 was retrieved from the brain cortex, whereas during the T4 infusion 40-50% of serum rT3 was found demonstrating that brain cortex rT3 is locally produced.