Thyroid hormones and its role in fish stress
Soibam Khogen Singh *
Thyroxine (T(4)) and triiodothyronine (T(3)), the principal thyroid hormones (THs) secreted from the hypothalamic-pituitary-thyroid (HPT) axis, produce a plethora of physiologic actions in fish.
The diverse actions of THs in fishes are primarily due to the sensitivity of thyroid axis to many physical, chemical and biological factors of both intrinsic and extrinsic origins.
The regulation of THs homeostasis becomes more complex due to extrathyroidal deiodination pathways by which the delivery of biologically active T(3) to target cells has been controlled.
As primary stress hormones and the end products of hypothalamic-pituitary-interrenal (HPI) and brain-sympathetic-chromaffin (BSC) axes, cortisol and adrenaline exert its actions on its target tissues where it promote and integrate osmotic and metabolic competence.
Despite possessing specific osmoregulatory and metabolic actions at cellular and whole-body levels, THs may fine-tune these processes in accordance with the actions of hormones like cortisol and adrenaline.
Evidences are presented that THs can modify the pattern and the magnitude of stress response in fishes as it modifies either its own actions or the actions of stress hormones.
In addition, multiple lines of evidence indicate that hypothalamic and pituitary hormones of thyroid and interrenal axes can interact with each other which in turn may regulate THs/cortisol-mediated actions.
Even though it is hard to define these interactions, the magnitude of stress response in fish has been shown to be modified by the changes in the status of THs, pointing to its functional relationship with endocrine stress axes particularly with the interrenal axis.
The fine-tuned mechanism that operates in fish during stressor-challenge drives the THs to play both fundamental and modulator roles in stress response by controlling osmoregulation and metabolic regulation. A major role of THs in stress response is thus evident in fish.
* Soibam Khogen Singh contributes to e-pao.net regularly. The writer is Ph.D., Aquaculture Division at Central Institute of Fisheries Education, Mumbai – 400061
The writer can be contacted at gengang(at)gmail(dot)com
This article was posted on September 06, 2011.
* Comments posted by users in this discussion thread and other parts of this site are opinions of the individuals posting them (whose user ID is displayed alongside) and not the views of e-pao.net. We strongly recommend that users exercise responsibility, sensitivity and caution over language while writing your opinions which will be seen and read by other users. Please read a complete Guideline on using comments on this website.