Physiological and pharmacological influences on thyroxine to 3,5,3'-triiodothyronine conversion and nuclear 3,5,3'-triiodothyronine binding in rat anterior pituitary.
Physiological and pharmacological influences on thyroxine to 3,5,3'-triiodothyronine conversion and nuclear 3,5,3'-triiodothyronine binding in rat anterior pituitary.
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对大鼠垂体前叶甲状腺素向 3,5,3-三碘甲状腺原氨酸转化和核 3,5,3-三碘甲状腺原氨酸结合的生理和药理学影响。
DOI：
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发表时间：
1979
影响因子：
15.9
通讯作者：
P. Larsen
中科院分区：
文献类型：
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作者：
R. Cheron;M. Kaplan;P. Larsen
我们最近的体内研究表明，垂体内L-甲状腺素（T（4））转化为3，5，3 '-三碘-L-甲状腺原氨酸（T（3））并随后与T（3）核结合是循环T（4）抑制促甲状腺激素释放的重要途径。本研究旨在探讨不同的生理和药理作用对大鼠垂体前叶组织中这两个过程的影响。将完整的垂体片段在含有0.14 ng/ml [（131）I]T（3）和3.8 ng/ml [（125）I]T（4）的1%牛血清白蛋白缓冲液中孵育。孵育3小时后分离细胞核，并通过纸色谱法鉴定结合的碘甲腺原氨酸。有0.3-1%的[（125）I]T（3）污染培养基[（125）I]T（4），并且在孵育期间没有变化。核[（125）I]T（4）并没有被过量的中等T（3）或T（4）降低650倍，这表明它是非特异性结合的。细胞核与培养基[（131）I]-和[（125）I]T（3）的比值表示为每分钟每毫克组织湿重的细胞核计数：每分钟每微升培养基的计数。[（131）I]T（3）的核：中（N：M）比值为0.45+/-0.21，而[（125）I] T（3）的核：中（N：M）比值为2.23+/-1.28（平均值+/-SD，n = 51），这一事实证明了垂体内T（4）向T（3）的转化。比值（R），即N：M [（125）I]T（3）除以N：M [（131）I]T（3），被用作垂体内T（4）向T（3）转化的指标。将培养基中T（3）浓度增加至50 ng/ml，导致两种T（3）同位素的N：M比值逐渐降低，但R值没有变化，表明两者竞争相同的有限容量核受体。增加培养基T（4）的浓度不会引起N：M [（131）I]T（3）的变化，但在四个实验中的三个中确实引起R的显著降低。这些结果表明，T（4）-5 '-单脱碘的饱和发生在较低的T（4）浓度比核T（3）结合位点的饱和。在甲状腺功能减退大鼠中，[（131）I]T（3）和[（125）I]T（3）的N：M比值均增加（P < 0.005），但R比对照组高3倍（P < 0.005）。每天给予10 μ g T（4）/100 g体重5天的动物，[（131）I]T（3）和[（125）I]T（3）的N：M比值显著降低，R值也降低。在禁食大鼠中，N：M比值均未降低，尽管相同动物的肝脏T（4）至T（3）转化率为对照组的50%（P < 0.005）。碘番酸（13 μ M），而不是6-正丙基硫氧嘧啶（29 μ M），降低N：M [（125）I]T（3），R值显著降低（P < 0.025或更低）。碘化钠（6 μ M）和促甲状腺激素释放激素（7-700 nM）均不影响T（3）N：M比值。这些结果表明，垂体内T（4）向T（3）的转化在甲状腺功能减退时受到刺激，而在T（4）处理的动物中受到抑制，而在肝T（4）-5 '-单脱碘中发生相反的变化。与肝脏不同，垂体前叶T（4）-5 '-单脱碘不受禁食或与6-n-丙基-2-硫氧嘧啶孵育的影响，但碘番酸抑制两者中T（4）向T（3）的转化。这些结果表明，垂体前叶对T（4）-5 '-单脱碘的调节与其它组织有重要的不同。
Our recent in vivo studies have suggested that intrapituitary l-thyroxine (T(4)) to 3,5,3'-triiodo-l-thyronine (T(3)) conversion with subsequent nuclear binding of T(3) is an important pathway by which circulating T(4) can inhibit thyrotropin release. The present studies were performed to evaluate various physiological and pharmacological influences on these two processes in rat anterior pituitary tissue. Intact pituitary fragments were incubated in buffer-1% bovine serum albumin containing 0.14 ng/ml [(131)I]T(3) and 3.8 ng/ml [(125)I]T(4). Nuclei were isolated after 3 h of incubation and the bound iodothyronines identified by paper chromatography. There was 0.3-1% [(125)I]T(3) contaminating the medium [(125)I]T(4), and this did not change during incubation. Nuclear [(125)I]T(4) was not decreased by 650-fold excesses of medium T(3) or T(4), suggesting that it was nonspecifically bound. The ratio of nuclear to medium [(131)I]- and [(125)I]T(3) were expressed as nuclear counts per minute per milligram wet weight of tissue:counts per minute per microliter medium. Intrapituitary T(4) to T(3) conversion was evidenced by the fact that the nuclear:medium (N:M) ratio for [(131)I]T(3) was 0.45+/-0.21, whereas that for [(125)I]T(3) was 2.23+/-1.28 (mean+/-SD, n = 51). A ratio (R), the N:M [(125)I]T(3) divided by the N:M [(131)I]T(3), was used as an index of intrapituitary T(4) to T(3) conversion. Increasing medium T(3) concentrations up to 50 ng/ml caused a progressive decrease in the N:M ratio for both T(3) isotopes, but no change in the value for R, indicating that both competed for the same limited-capacity nuclear receptors. Increasing concentrations of medium T(4) caused no change in the N:M [(131)I]T(3) but did cause a significant decrease in R in three of four experiments. These results suggest saturation of T(4)-5'-monodeiodination occurred at lower T(4) concentrations than saturation of nuclear T(3) binding sites. In hypothyroid rats, the N:M ratios for both [(131)I]T(3) and [(125)I]T(3) were increased (P < 0.005), but R was three-fold higher than in controls (P < 0.005). Animals given 10 mug T(4)/100 g body wt per d for 5 d had significantly decreased N:M ratios for both [(131)I]T(3) and [(125)I]T(3), as well as a decreased value for R. In fasted rats, neither N:M ratio was depressed, although hepatic T(4) to T(3) conversion in the same animals was 50% of control (P < 0.005). Iopanoic acid (13 muM), but not 6-n-propylthiouracil (29 muM), decreased the N:M [(125)I]T(3) with a significant decrease in the value for R (P < 0.025 or less). Neither sodium iodide (6 muM) nor thyrotropin-releasing hormone (7-700 nM) affected the T(3) N:M ratios. These results indicate that intrapituitary T(4) to T(3) conversion is stimulated in hypothyroidism and depressed in T(4)-treated animals, whereas opposite changes occur in hepatic T(4)-5'-monodeiodination. Unlike liver, anterior pituitary T(4)-5'-monodeiodination is not affected by fasting or incubation with 6-n-propyl-2-thiouracil, but T(4) to T(3) conversion is inhibited in both by iopanoic acid. These results indicate that there are important differences between anterior pituitary and other tissues in the regulation of T(4)-5'-monodeiodination.