Putative nuclear triiodothyronine receptors in tadpole liver during metamorphic climax.
Putative nuclear triiodothyronine receptors in tadpole liver during metamorphic climax.
复制标题
DOI：
10.1210/endo-117-3-912
复制
发表时间：
1985-09
期刊：
影响因子：
4.8
通讯作者：
V. Galton;D. S. St. Germain
中科院分区：
文献类型：
--
作者：
V. Galton;D. S. St. Germain
以前已经表明，蝌蚪红细胞（RBC）中假定的T3受体的最大结合容量（MBC）在发育过程中增加，并且可以通过甲状腺激素（TH）刺激。本研究旨在确定蝌蚪肝细胞核的MBC是否在发育过程中或TH处理后也增加。由于相对较高水平的内源性TH在蝌蚪在高潮期间，使用体内饱和度测定采用[125 I]T3是不可行的。因此，MBC通过RIA测量结合到用足够的T3使受体饱和的预处理的蝌蚪的肝核的T3的量来确定。然后使用在给予大剂量T3（10 nmol）的蝌蚪中获得的数据对不饱和部分的值进行校正。在这一剂量之后，基本上细胞核中所有的T3都被结合到不饱和位点。通过该方法和Scatchard分析估计的MBC值具有可比性。与蝌蚪红细胞中的观察结果相反，随着蝌蚪从早期前变态到变态高潮的进展，肝核的MBC没有发生显著变化;在阶段XII-XIV和XIX-XXIII的蝌蚪中，MBC值分别为0.308 +/- 0.024（+/- SE）和0.260 +/- 0.035 pmol/mg DNA。此外，T4（1 nmol T4;研究前14天），这导致在红细胞受体数量显着增加的蝌蚪治疗，肝细胞核MBC没有影响。还测定了肝脏和红细胞中与核结合的内源性T3的量。根据这些数据和MBC值，计算出肝脏和RBC核受体分别占T3的80%和90%以上。这些结果表明，变态期MBC受体对TH的反应具有组织特异性，顶极期MBC受体上的TH主要是T_3。
It has been shown previously that the maximum binding capacity (MBC) of the putative T3 receptors in tadpole red blood cells (RBCs) is increased during development and can be stimulated by treatment with thyroid hormone (TH). The present study was performed to determine if the MBC of tadpole liver nuclei is also increased during development or after treatment with TH. Because of the relatively high levels of endogenous TH in tadpoles during climax, the use of an in vivo saturation assay employing [125I]T3 was not feasible. Thus, MBC was determined by measuring by RIA the amount of T3 bound to the liver nuclei in tadpoles pretreated with sufficient T3 to saturate the receptors. Values were then corrected for the nonsaturable fraction using data obtained in tadpoles given a large dose of T3 (10 nmol). After this dose, essentially all of the T3 in the nucleus was bound to nonsaturable sites. MBC values estimated by this method and by Scatchard analysis were comparable. In contrast to the observations in tadpole RBCs, no significant change in the MBC of liver nuclei occurred as the tadpole progressed from early prometamorphosis to metamorphic climax; in tadpoles at stages XII-XIV and XIX-XXIII, MBC values were 0.308 +/- 0.024 (+/- SE) and 0.260 +/- 0.035 pmol/mg DNA, respectively. Furthermore, treatment of tadpoles with T4 (1 nmol T4; 14 days before study), which resulted in a marked increase in receptor number in RBCs, had no effect on MBC in hepatic nuclei. The amounts of nucleus-bound endogenous T3 in liver and RBCs were also determined. From these data and the MBC values, it was calculated that hepatic and RBC nuclear receptors were, respectively, 80% and more than 90% occupied with T3. These findings indicate that there is tissue specificity in the response of receptor MBC to TH during metamorphosis, and that most of the TH on the receptor during climax is T3.