Mukhi Sandeep, Torres Leticia, Patiño Reynaldo
Department of Environmental Toxicology and Texas Cooperative Fish and Wildlife Research Unit, Texas Tech University, Lubbock, TX 79409-1160, USA.
Gen Comp Endocrinol. 2007 Feb;150(3):486-94. doi: 10.1016/j.ygcen.2006.11.013. Epub 2006 Dec 28.
The objective of this study was to determine the effect of larval-juvenile exposure to perchlorate, a thyroid hormone synthesis inhibitor, on the establishment of gonadal sex ratios in zebrafish. Zebrafish were exposed to untreated water or water containing perchlorate at 100 or 250 ppm for a period of 30 days starting at 3 days postfertilization (dpf). Recovery treatments consisted of a combination of perchlorate and exogenous thyroxine (T4; 10 nM). Thyroid histology was assessed at the end of the treatment period (33 dpf), and gonadal histology and sex ratios were determined in fish that were allowed an additional 10-day period of growth in untreated water. As expected, exposure to perchlorate caused changes in thyroid histology consistent with hypothyroidism and these effects were reversed by co-treatment with exogenous T4. Perchlorate did not affect fish survival but co-treatment with T4 induced higher mortality. However, relative to the corresponding perchlorate concentration, co-treatment with T4 caused increased mortality only at a perchlorate concentration of 100 ppm. Perchlorate alone or in the presence of T4 suppressed body length at 43 dpf relative to control values. Perchlorate exposure skewed the sex ratio toward female in a concentration-dependent manner, and co-treatment with T4 not only blocked the feminizing effect of perchlorate but also overcompensated by skewing the sex ratio towards male. Moreover, co-treatment with T4 advanced the onset of spermatogenesis in males. There was no clear association between sex ratios and larval survival or growth. We conclude that endogenous thyroid hormone plays a role in the establishment of gonadal sex phenotype during early development in zebrafish.
本研究的目的是确定幼鱼-幼年期暴露于甲状腺激素合成抑制剂高氯酸盐对斑马鱼性腺性别比例确立的影响。斑马鱼在受精后3天（dpf）开始，暴露于未处理的水或含有100或250 ppm高氯酸盐的水中30天。恢复处理包括高氯酸盐和外源性甲状腺素（T4；10 nM）的组合。在处理期结束时（33 dpf）评估甲状腺组织学，并在未处理的水中再生长10天的鱼中确定性腺组织学和性别比例。如预期的那样，暴露于高氯酸盐会导致与甲状腺功能减退一致的甲状腺组织学变化，并且这些影响通过与外源性T4共同处理而逆转。高氯酸盐不影响鱼类存活，但与T4共同处理会导致更高的死亡率。然而，相对于相应的高氯酸盐浓度，仅在高氯酸盐浓度为100 ppm时，与T4共同处理才会导致死亡率增加。相对于对照值，单独的高氯酸盐或在T4存在下均会抑制43 dpf时的体长。高氯酸盐暴露以浓度依赖的方式使性别比例偏向雌性，并且与T4共同处理不仅阻断了高氯酸盐的雌性化作用，而且通过使性别比例偏向雄性而过度补偿。此外，与T4共同处理会使雄性精子发生的开始提前。性别比例与幼鱼存活或生长之间没有明显关联。我们得出结论，内源性甲状腺激素在斑马鱼早期发育过程中性腺性别表型的确立中起作用。
