Binding of thyroid hormones in vivo by hepatic nuclei of Rana catesbeiana tadpoles.
Binding of thyroid hormones in vivo by hepatic nuclei of Rana catesbeiana tadpoles.
复制标题
林蛙蝌蚪肝细胞核与体内甲状腺激素的结合。
DOI：
10.1210/endo-106-3-859
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发表时间：
1980
期刊：
影响因子：
4.8
通讯作者：
V. Galton
中科院分区：
文献类型：
--
作者：
V. Galton
甲状腺激素对于两栖动物的变态至关重要，蝌蚪在发育前阶段会对外源 T4 和 T3 产生反应。目前的研究是为了调查与这种反应的启动有关的受体。将[125I]T3或[125I]T4（0.001-10nmol/蝌蚪）腹腔注射给变态前蝌蚪（Taylor和Kollros的VII-XV阶段）。 24小时后，获取肝脏和血清，并测量肝细胞核和血清中的有机125I（显示为未变化的激素）。 T3 和 T4 的饱和结合位点均存在于肝细胞核中。结合数据分析表明，T3 的 Kd 平均值为 1.6 x 10(-12) M（每升血浆中游离 T3 的摩尔数），最大结合能力平均值为 0.1 ng/mg DNA。对于 T4，平均 Kd 为 3.9 x 10(-15 M，平均最大结合能力为 0.5 ng/mg DNA。据估计，这些位点的很大一部分通常不被内源激素占据。T3 结合位点的特性在 X 和 XV 阶段的蝌蚪中相似。稳定的 T4 以及 T3 的乙酸和丙酸类似物与 [125I]T3 竞争这些位点几乎和 [125I]T3 一样容易。 T4 的乙酸类似物、D-T4、3,5-二碘甲状腺原氨酸和 rT3 等活性较低的类似物，在 4°C 保存的蝌蚪中，T3 与饱和核结合位点的结合减少，但与非饱和核结合位点的结合减少。根据这些发现，表明这些核结合位点是甲状腺激素受体。
Thyroid hormone is essential for amphibian metamorphosis, and tadpoles develop responsiveness to exogenous T4 and T3 during the premetamorphic stage of development. The present studies were performed to investigate the receptors concerned with the initiation of this response. Premetamorphic tadpoles (stages VII-XV of Taylor and Kollros) were injected ip with [125I]T3 or [125I]T4 (0.001-10 nmol/tadpole). Twenty-four hours later, liver and serum were obtained, and organic 125I in liver nuclei and serum (shown to be unchanged hormone) was measured. Saturable binding sites for both T3 and T4 were present in the liver nuclei. Analysis of binding data indicated for T3 a mean value for Kd of 1.6 x 10(-12) M (moles of free T3 per liter plasma) and a mean value for maximum binding capacity of 0.1 ng/mg DNA. For T4, the mean Kd was 3.9 x 10(-15 M, and the mean maximum binding capacity was 0.5 ng/mg DNA. It was estimated that a significant fraction of these sites was not normally occupied by endogenous hormone. Properties of the T3-binding sites were similar in tadpoles at stages X and XV. Stable T4 and the acetic and propionic acid analogs of T3 competed with [125I]T3 for the sites almost as readily as did stable T3. The acetic acid analog of T4, D-T4, 3,5-diiodothyronine, and rT3, less active analogs, were relatively poor competitors. Binding of T3 to saturable but not to non-saturable nuclear binding sites was reduced in tadpoles kept at 4 C. On the basis of these findings, it is suggested that these nuclear binding sites are thyroid hormone receptors.