Degitz Sigmund J, Holcombe Gary W, Kosian Patricia A, Tietge Joseph E, Durhan Elizabeth J, Ankley Gerald T
U.S. Environmental Protection Agency, Mid-Continent Ecology Division, 6201 Congdon Boulevard, Duluth, Minnesota 55804, USA.
Toxicol Sci. 2003 Jul;74(1):139-46. doi: 10.1093/toxsci/kfg098. Epub 2003 May 28.
Recently, high frequencies of malformations have been reported in amphibians across the United States. It has been suggested that the malformations may be the result of xenobiotic disruption of retinoid signaling pathways during embryogenesis and tadpole development. Therefore, a series of experiments were undertaken to examine life-stage specific effects of continuous retinoid exposure on Xenopus laevis. Continuous all-trans retinoic acid (RA) concentrations were delivered using a column saturator and a flow-through diluter system. Stage 8 embryos were exposed to RA concentrations ranging from 0.013 to 2 microgram/l. At the onset of hindlimb bud emergence (NF stage 48), a subset of tadpoles was moved to clean water, and remaining organisms were exposed continuously through metamorphosis. In addition, early limb-bud-stage tadpoles were exposed for 1 week, 2 weeks, or until tail resorption was complete, to eight concentrations of RA in the range of 0.031-3 microgram/l. RA exposure resulted in a concentration-dependent increase in mortality and dysmorphogenesis in embryos at concentrations of 0.24 microgram/l and above. However, this early embryonic exposure did not result in hindlimb abnormalities in surviving tadpoles allowed to mature in clean water. RA did not induce limb malformations in any surviving tadpole exposed during larval stages. We are confident that the concentrations used were high enough, given that the highest concentration used resulted in 100% mortality within 2 weeks of initiating the exposure. This result suggests that other aspects of growth and development, which are not externally obvious, are more sensitive to retinoids than skeletal development. From these experiments and our previous work, we conclude that it is unlikely that retinoid mimics would produce the spectrum of limb malformations which recently have been observed in amphibians collected from the field.
最近，美国各地都报告了两栖动物中出现高频率畸形的情况。有人认为，这些畸形可能是胚胎发育和蝌蚪发育过程中类视黄醇信号通路受到异生素干扰的结果。因此，开展了一系列实验，以研究持续暴露于类视黄醇对非洲爪蟾不同生命阶段的特定影响。使用柱式饱和器和流通稀释系统提供连续的全反式视黄酸（RA）浓度。将8期胚胎暴露于浓度范围为0.013至2微克/升的RA中。在后肢芽出现时（NF 48期），将一部分蝌蚪转移到清水中，其余的生物体则持续暴露至变态结束。此外，将早期肢芽期的蝌蚪暴露于浓度范围为0.031至3微克/升的八种RA浓度下1周、2周或直至尾巴完全吸收。当RA浓度达到0.24微克/升及以上时，胚胎的死亡率和畸形发生呈浓度依赖性增加。然而，这种早期胚胎暴露并未导致在清水中成熟的存活蝌蚪出现后肢异常。RA在幼虫阶段暴露的任何存活蝌蚪中均未诱导肢体畸形。鉴于所使用的最高浓度在开始暴露后2周内导致100%的死亡率，我们相信所使用的浓度足够高。这一结果表明，生长和发育的其他方面（这些方面在外部并不明显）比骨骼发育对类视黄醇更敏感。从这些实验以及我们之前的工作中，我们得出结论，类视黄醇类似物不太可能产生最近在野外采集的两栖动物中观察到的肢体畸形谱。
