College of Life Science, Shaanxi Normal University, Xi'an, 710119, China.
School of Environmental Science and Engineering, Chang'an University, Xi'an, 710054, China; Key Laboratory of Subsurface Hydrology and Ecological Effect in Arid Region of Ministry of Education, Xi'an, 710062, China.
Chemosphere. 2019 Dec;236:124251. doi: 10.1016/j.chemosphere.2019.06.221. Epub 2019 Jun 29.
We examined the Pb exposure on tadpoles of Bufo gargarizans from Gosner stage 26-42. Mortality, growth and development, time to metamorphosis, size, and skeletal ossification at metamorphic climax of Bufo gargarizans were examined. Also, histological characteristics of thyroid glands in tadpoles at Gosner stage 33, 38, and 42 as well as transcript levels of thyroid hormone-related genes in the hind-limb, tail, and liver of tadpoles at metamorphic climax were examined. Pb exposure induced mortality in a concentration-dependent manner in Bufo gargarizans larvae. The significant increase in growth and development, percent metamorphosis, size at metamorphic climax, and skeletal ossification were observed at 50 μg Pb L; however, exposure to 1000 μg Pb L resulted in the opposite effects in tadpoles. In addition, histological alterations of thyroid gland, such as follicular cell hyperplasia and colloid depletion could be found in 50-1000 μg Pb L treatments. Furthermore, Pb exposure at 1000 μg L resulted in significantly decreased transcript levels of Dio2, TRα and TRβ, and increased transcript levels of Dio3. In contrast, 50 μg Pb L significantly upregulated the mRNA levels of Dio2, TRα, and TRβ, but it reduced the Dio3 expression. These results suggested that Pb might disrupt TH homeostasis in tadpoles by histological alterations of thyroid gland and disturb the transcript levels of Dio2, Dio3, TRα, and TRβ, leading to altered growth and development, as well as percent metamorphosis and skeletal ossification. Further studies are needed to elucidate the underlying mechanisms of low-dose stimulation and high-dose inhibition effects.
我们研究了 26-42 期的 gosner 蛙卵蝌蚪对铅暴露的反应。我们检查了死亡率、生长和发育、变态时间、大小和变态高峰期骨骼骨化情况。还检查了 33、38 和 42 期蝌蚪甲状腺组织学特征以及变态高峰期蝌蚪后肢、尾巴和肝脏中甲状腺激素相关基因的转录水平。Pb 暴露以浓度依赖的方式诱导 gosner 期蝌蚪死亡。在 50μg Pb L 时，观察到生长和发育、变态率、变态高峰期大小和骨骼骨化显著增加；然而，在 1000μg Pb L 时，暴露导致蝌蚪出现相反的效果。此外，在 50-1000μg Pb L 处理中发现甲状腺滤泡细胞增生和胶体耗竭等甲状腺组织学改变。此外，Pb 暴露在 1000μg L 时，Dio2、TRα 和 TRβ 的转录水平显著降低，Dio3 的转录水平增加。相比之下，50μg Pb L 显著上调了 Dio2、TRα 和 TRβ 的 mRNA 水平，但降低了 Dio3 的表达。这些结果表明，Pb 可能通过甲状腺组织学改变和干扰 Dio2、Dio3、TRα 和 TRβ 的转录水平来破坏蝌蚪的 TH 稳态，导致生长和发育、变态率以及骨骼骨化改变。需要进一步研究来阐明低剂量刺激和高剂量抑制作用的潜在机制。
