Cecconi S, Rucci N, Scaldaferri M L, Masciulli M P, Rossi G, Moretti C, D'Armiento M, Ulisse S
Department of Experimental Medicine, University of L'Aquila, Italy.
Endocrinology. 1999 Apr;140(4):1783-8. doi: 10.1210/endo.140.4.6635.
In the present study we evaluated the role of T3 on the in vitro processes of mouse cumulus cell-oocyte complex expansion, oocyte meiotic maturation, and granulosa cell aromatase activity. Results obtained from cumuli oophori isolated from immature and adult mice ovaries demonstrated that T3 at all concentrations tested (0.1-100 nM) did not affect basal or FSH-induced cumulus expansion or interfere with oocyte meiotic maturation up to metaphase II stage. On the contrary, T3 inhibited in a time- and dose-dependent manner FSH-induced aromatase activity in cultured granulosa cells obtained from either adult or immature female mice. The half-maximal dose (ED50) of T3 inhibition was 0.87 +/- 0.21 nM, which is in agreement with the reported dissociation constant of T3 nuclear receptor (Kd = 0.4-5 nM) in mammalian granulosa cells. Time-course experiments demonstrated higher sensitivity to T3 of adult granulosa cells with respect to immature granulosa cells in culture. Indeed, in immature granulosa cells T3 inhibition became significantly evident only after 6 days of hormonal treatment, whereas in adult granulosa cells the inhibitory effect was present after only 2 days of treatment. (Bu)2cAMP- or 3-isobutyl-1-methyl-xanthine-stimulated aromatase activity was also significantly decreased by T3, thus suggesting that the inhibition was downstream from cAMP formation. Lastly, analysis of aromatase messenger RNA (mRNA) levels by semiquantitative RT-PCR demonstrated the ability of FSH to increase aromatase mRNA level in cultured granulosa cells by 2.4 +/- 0.5-fold. In agreement with the effect on enzyme activity, the stimulatory effect of FSH on aromatase mRNA level was greatly reduced after T3 cotreatment. In conclusion, T3 inhibition of aromatase activity may be of physiological relevance in the complex multihormonal regulation of mammalian follicle development and may contribute to explaining the alteration in female reproductive functions after thyroid hormone hypo- or hypersecretion.
在本研究中，我们评估了T3对小鼠卵丘细胞-卵母细胞复合体体外扩张、卵母细胞减数分裂成熟以及颗粒细胞芳香化酶活性过程的作用。从未成熟和成年小鼠卵巢分离得到的卵丘细胞的实验结果表明，所有测试浓度（0.1 - 100 nM）的T3均不影响基础或FSH诱导的卵丘扩张，也不干扰卵母细胞减数分裂至中期II阶段的成熟过程。相反，T3以时间和剂量依赖性方式抑制从成年或未成熟雌性小鼠获得的培养颗粒细胞中FSH诱导的芳香化酶活性。T3抑制的半数最大剂量（ED50）为0.87±0.21 nM，这与报道的哺乳动物颗粒细胞中T3核受体的解离常数（Kd = 0.4 - 5 nM）一致。时间进程实验表明，培养中的成年颗粒细胞对T3的敏感性高于未成熟颗粒细胞。实际上，在未成熟颗粒细胞中，仅在激素处理6天后T3抑制才明显显著，而在成年颗粒细胞中，仅在处理2天后就出现了抑制作用。(Bu)2cAMP或3 - 异丁基 - 1 - 甲基 - 黄嘌呤刺激的芳香化酶活性也因T3而显著降低，这表明抑制作用发生在cAMP形成的下游。最后，通过半定量RT - PCR分析芳香化酶信使RNA（mRNA）水平表明，FSH能够使培养颗粒细胞中的芳香化酶mRNA水平增加2.4±0.5倍。与对酶活性的影响一致，T3共同处理后，FSH对芳香化酶mRNA水平的刺激作用大大降低。总之，T3对芳香化酶活性的抑制在哺乳动物卵泡发育的复杂多激素调节中可能具有生理相关性，并且可能有助于解释甲状腺激素分泌不足或分泌过多后女性生殖功能的改变。
