In this study, healthy Wuchang bream (Megalobrama amblycephala) juveniles were exposed to 0, 5, 10, 20 and 30 mg/L total ammonia nitrogen for 30 days to elucidate toxic effects and mechanisms of ammonia on growth performance involved with the regulation of growth hormone/insulin‐like growth factor (GH/IGF) and hypothalamic–pituitary‐thyroid (HPT) axes. Our results showed that the increasing total ammonia nitrogen concentrations caused dose‐depend decreases in the weight gain and specific growth rate but increases in the food conversion ratio and mortality in juvenile bream, indicating growth inhibitory effects induced by ammonia. Concurrently, GH, IGF‐1 at protein and mRNA levels were significantly decreased in ammonia exposure groups (p < .05), while serum thyroid stimulating hormone, free thyroxine, free triiodothyronine levels were significantly reduced only in fish exposed to higher concentrations of 20 and 30 mg/L ammonia (p < .05), suggesting that ammonia exposure could perturb both GH/IGF‐axis and HPT‐axis functions. Furthermore, transcriptional levels of extracellular regulated protein kinases 2 (erk2), phosphatidylinositol 3‐kinase (pi3k), protein kinase B (akt), target of rapamycin (tom) and ribosomal protein S6 kinase‐polypeptide 1(s6k1) in the dorsal muscle were significantly down‐regulated in the fish exposed to ammonia (p < .05). This fact indicated that MAPK/ERK pathway and PI3K/AKT pathway should be responsible for the growth inhibition. Combining the results of spearman correlation coefficient, it should be noted that the GH/IGF axis played a more important role in regulating the growth than the HPT axis in Wuchang bream under persistent ammonia stress.

中文翻译：

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慢性亚氨暴露主要通过下调生长激素/胰岛素样生长因子轴来抑制幼武昌（Megalobrama amblycephala）的生长。

在这项研究中，健康的武昌（Megalobrama amblycephala）幼鱼被暴露于总氨氮分别为0、5、10、20和30 mg / L 30天，以阐明氨的毒性作用和与生长调节有关的生长性能机制。激素/胰岛素样生长因子（GH / IGF）和下丘脑-垂体-甲状腺（HPT）轴。我们的研究结果表明，总氨氮浓度的增加导致体重增加和比生长速率的剂量依赖性降低，但幼鱼的食物转化率和死亡率增加，表明氨诱导的生长抑制作用。同时，氨暴露组的蛋白质和mRNA水平的GH，IGF-1显着降低（p <.05），而仅在暴露于20和30 mg / L较高浓度氨的鱼中，血清甲状腺刺激激素，游离甲状腺素，游离三碘甲状腺素水平显着降低（p  <.05），这表明氨暴露可干扰两个GH / IGF轴和HPT轴功能。此外，背侧肌肉中细胞外调节蛋白激酶2（erk2），磷脂酰肌醇3激酶（pi3k），蛋白激酶B（akt），雷帕霉素的靶标（tom）和核糖体蛋白S6激酶多肽1（s6k1）的转录水平。暴露于氨水的鱼中的蛋白显着下调（p <.05）。这一事实表明，MAPK / ERK途径和PI3K / AKT途径应负责抑制生长。结合斯皮尔曼相关系数的结果，应该指出，在持续氨胁迫下，武昌鲷的GH / IGF轴在调节生长方面起着比HPT轴更重要的作用。