title: Effects of nitrate on metamorphosis, thyroid and iodothyronine deiodinases expression in Bufo gargarizans larvae.
abstract: Chinese toad (Bufo gargarizans) tadpoles were exposed to nitrate (10, 50 and 100mg/L NO3-N) from the beginning of the larval period through metamorphic climax. We examined the effects of chronic nitrate exposure on metamorphosis, mortality, body size and thyroid gland. In addition, thyroid hormone (TH) levels, type II iodothyronine deiodinase (Dio2) and type III iodothyronine deiodinase (Dio3) mRNA levels were also measured to assess disruption of TH synthesis. Results showed that significant metamorphic delay and mortality increased were caused in larvae exposed to 100mg/L NO3-N. The larvae exposed to 100mg/L NO3-N clearly exhibited a greater reduction in thyroxine (T4) and 3,5,3'-triiodothyronine (T3) levels. Moreover, treatment with NO3-N induced down-regulation of Dio2 mRNA levels and up-regulation of Dio3 mRNA levels, reflecting the disruption of thyroid endocrine. It seems that increased mass and body size may be correlated with prolonged metamorphosis. Interestingly, we observed an exception that exposure to 100mg/L NO3-N did not exhibit remarkable alterations of thyroid gland size. Compared with control groups, 100mg/L NO3-N caused partial colloid depletion in the thyroid gland follicles. These results suggest that nitrate can act as a chemical stressor inducing retardation in development and metamorphosis. Therefore, we concluded that the presence of high concentrations nitrate can influence the growth, decline the survival, impair TH synthesis and induce metamorphosis retardation of B. gargarizans larvae.
authors.affiliation: College of Life Science, Shaanxi Normal University, Xi'an 710119, China.
authors.forename: Ming
authors.initials: M
authors.lastname: Wang
authors.affiliation: 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.
authors.forename: Lihong
authors.initials: L
authors.lastname: Chai
authors.affiliation: College of Life Science, Shaanxi Normal University, Xi'an 710119, China.
authors.forename: Hongfeng
authors.initials: H
authors.lastname: Zhao
authors.affiliation: College of Life Science, Shaanxi Normal University, Xi'an 710119, China.
authors.forename: Minyao
authors.initials: M
authors.lastname: Wu
authors.affiliation: College of Life Science, Shaanxi Normal University, Xi'an 710119, China. Electronic address: hongyuanwang@snnu.edu.cn.
authors.forename: Hongyuan
authors.initials: H
authors.lastname: Wang
mesh_terms: D000818:Animals; D002025:Bufonidae / Q000235:genetics* / Q000254:growth & development*; D015536:Down-Regulation / Q000187:drug effects; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects*; D007453:Iodide Peroxidase / Q000235:genetics*; D007814:Larva / Q000187:drug effects / Q000235:genetics / Q000254:growth & development; D008675:Metamorphosis, Biological / Q000187:drug effects*; D009566:Nitrates / Q000633:toxicity*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D013961:Thyroid Gland / Q000187:drug effects* / Q000378:metabolism; D013974:Thyroxine / Q000378:metabolism; D014284:Triiodothyronine / Q000378:metabolism; D015854:Up-Regulation / Q000187:drug effects; D014874:Water Pollutants, Chemical / Q000633:toxicity; D000097564:Iodothyronine Deiodinase Type II
chemical_list: D007453:Iodide Peroxidase; D009566:Nitrates; D012333:RNA, Messenger; D013974:Thyroxine; D014284:Triiodothyronine; D014874:Water Pollutants, Chemical; D000097564:Iodothyronine Deiodinase Type II; C117274:iodothyronine deiodinase type III
keywords: Bufo gargarizans; Iodothyronine deiodinase; Metamorphosis; Nitrate; Thyroid hormone