Physiology of interrenal function in juvenile coho salmon (Oncorhynchus kisutch) and effects of hatchery rearing practices Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/np193c20n

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  • Periodic determinations of plasma hormone levels suggested that changes in interrenal activity are unrelated to changes in thyroidal or gonadal activity during development (smoltification) of juvenile coho salmon (Oncorhynchus kisutch). Moreover, in an experiment where fish were reared under various conditions of crowding and water inflow rate, it appeared that changes of interrenal activity were also unrelated to changes in gill Na/K-ATPase activity during smoltification. This finding placed some doubt on current hypotheses regarding the significance of interrenal tissue vis-a-vis osmoregulatory organs in fresh water during smoltification, since these hypotheses require a close positive correlation between changes in their activities. Also, the relationships I observed among the experimental rearing conditions (crowding and water inflow levels), water quality (oxygen and total dissolved ammonia levels), and the physiological status of the fish (plasma cortisol, thyroxine and triiodothyronine levels, and gill Na/K-ATPase activity) suggested that crowding stress itself is an important factor by which high rearing density affects the physiology of coho salmon. Lowering the rearing density from a high to a low level two weeks before sampling affected plasma cortisol but not plasma thyroxine or gill Na/K-ATPase. The main steroid secreted by unstimulated or ACTH-stimulated interrenal cells in vitro was cortisol. However, the main plasma corticosteroids were cortisol and cortisone, and the levels of both steroids increased during stress or seawater exposure. I concluded that cortisone arises from the peripheral transformation of cortisol and that a clarification of its significance is needed for an adequate understanding of corticosteroid physiology in teleosts. An increase in extracellular osmolality or sodium levels within the physiological range slightly enhanced the spontaneous release of cortisol by interrenal cells in vitro, but it did not affect the steroidogenic response of the cells to ACTH. Potassium enhanced steroid secretion only when elevated to pharmacological levels; changes within the physiological range of this ion did not have modulatory effects on ACTH-induced steroidogenesis. Thus, in contrast to findings in other classes of vertebrates changes in the levels of plasma monovalent ions or osmotic pressure may not be important factors directly regulating interrenal function in coho salmon. Treatment of interrenal cells with forskolin enhanced cortisol secretion in vitro, and hydrolysis-resistant ATP analogs depressed the response of the cells to ACTH. Analogs of cAMP, but not of cGMP, enhanced steroid secretion. Thus, as in most other vertebrates, cAMP is a major mediator of ACTH-induced steroidogenesis in interrenal cells of coho salmon. However, in contrast to previous findings in other vertebrates, phosphatidylinositol and cholera toxin did not affect interrenal steroidogenesis in coho salmon.
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