Role of cortisol in the physiological response to toxicants in fish

当生物体暴露在潜在的有害刺激下时，就会引起生理应激反应。皮质醇是鱼类组织水平反应的关键激素效应因子。许多物种和包括毒物在内的不同应激源的应激反应已有特征，但关键的基本问题仍然存在：在暴露于毒物期间，应激反应对机体有利还是有害；对毒物的脆弱性是否与反应的稳健性有关？这项拟议研究的目的是阐明皮质醇在鱼类对毒物的生理反应中的作用，并测试皮质醇在急性潜在致命毒物暴露下有有益影响，但在亚致死慢性暴露下是有害的，产生显著的代谢成本的假说。皮质醇应激反应模式与毒物易感性之间的关系将通过一种比较的、多物种的方法进行研究，该方法结合毒理学和应激生理学，结合整个动物实验室和野外暴露，对皮质醇状态的药理学操作和原代细胞培养。通过使用容器水皮质醇对单个鱼进行多次测量而获得的皮质醇反应模式，将在四个孵化养殖的鱼种(虹鱼幼鱼、溪鲑鱼、肥头鱼、金鱼)中进行表征，这些鱼种对测试毒物(亚硒酸盐、镉、农药农达)的易感性存在差异。下一步，皮质醇的状态将被药理学操控，要么用甲孕酮和RU 486阻断皮质醇分泌和皮质醇受体，要么用合成皮质醇升高皮质醇。然后，经皮质醇操纵的鱼类将在实验室或暴露于市政污水的网箱中急性或长期暴露于毒物。在能够进行正常应激反应的鱼类和皮质醇操纵的鱼中，将比较存活、生长、代谢和生殖状况、氧化应激以及包括HSP 70、STAR和HSD在内的特定基因的表达，以检验这样的假设，即强大但短暂的皮质醇应激反应使鱼类能够比长期反应或无反应更有效地处理毒物。在体外，虹鲑头肾细胞和受精卵将暴露在测试毒物中，无论是否在培养中加入皮质醇。将测量细胞活力、氧化应激、胚胎发育和基因表达，以提供毒理学数据并检验皮质醇在特定浓度和暴露时间具有保护作用的假设。拟议的研究将提供对皮质醇在毒物生理反应中的作用以及调节物种敏感性差异的机制的新理解。

The physiological stress response is elicited when organisms are exposed to potentially harmful stimuli. Cortisol is a key hormonal effector of the response at tissue level in fish. The stress response has been characterized for many species and diverse stressors, including toxicants, yet key fundamental questions remain: is the stress response beneficial or detrimental to the organism during exposure to toxicants; is vulnerability to toxicants related to robustness of the response? The goal of the proposed research is to elucidate the role of cortisol in the physiological response to toxicants in fish and test the hypothesis that cortisol has beneficial effects under acute potentially lethal toxicant exposures, but is detrimental, engendering significant metabolic costs, under sublethal chronic exposures. The relationship between the pattern of the cortisol stress response and vulnerability to toxicants will be investigated with a comparative, multispecies approach integrating toxicology and stress physiology, with whole animal laboratory and field exposures, pharmacological manipulations of the cortisol status and primary cell cultures. The patterns of the cortisol response, obtained from multiple measurements in individual fish using containment water cortisol, will be characterized in four hatchery-bred fish species (juvenile rainbow trout, brook trout, fathead minnow, goldfish) which display differences in vulnerability to test toxicants (selenite, cadmium, pesticide Roundup). Next, the cortisol status will be manipulated pharmacologically to either block cortisol secretion and cortisol receptors by metyrapone and RU 486, or elevate cortisol with synthetic cortisol. Cortisol-manipulated fish will then be exposed to toxicants acutely or chronically in the laboratory, or in cages at sites exposed to municipal effluents.  Survival, growth, metabolic and reproductive status, oxidative stress, and expression of specific genes including hsp 70, StAR, and HSD, will be compared in fish able to mount the normal stress response and in cortisol-manipulated fish, to test the hypothesis that a robust but brief cortisol stress response enables the fish to deal with toxicants more efficiently than a prolonged response or no response. In vitro, rainbow trout head kidney cells and fertilized eggs will be exposed to the test toxicants, with or without cortisol in the culture. Cell viability, oxidative stress, embryonic development and gene expression will be measured to provide toxicological data and test the hypothesis that cortisol, at specific concentrations and timing of the exposure, has protective effects. The proposed research will provide new understanding of the role of cortisol in the physiological response to toxicants and the mechanisms mediating species differences in sensitivity.**