Matters of the Heart and Sex: Cardiac Stress Physiology in Rainbow Trout

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The heart is an essential organ for survival.  Despite its physiological importance, very little is known about the effects of steroid hormones on cardiac function in fish.  Comparatively, this is a striking contrast to what is known about the role of such hormones in the development of heart disease in mammalian systems. Furthermore, very few studies have addressed the effects of environmental stress on the fish heart.  Our first goal was to understand how physical stress and endocrine disruptors affect gene expression, in juvenile rainbow trout (Oncorhynchus mykiss). By studying differential gene expression, we can identify the underlying molecular mechanisms forming the basis for physiological change.  We have found that the genes glucocorticoid receptor 2, nuclear protein 1, and junb increase in response to physical stress in the heart.   Further, ethinyl estradiol (EE₂), the active ingredient in birth control pills, and a known endocrine disruptor in fish, changed resting levels of cardiac genes vitellogenin 1, estrogen receptor and androgen receptor following a 7-day exposure.  The implications and functions of these genes will be discussed.  Such results illustrate that environmental stressors affect cardiac tissue in fish at the cellular level.  

Our second goal was to determine the effect of exposure to EE₂ on cardiac function.  Contractility from ventricle tissue preparations, in vitro, was measured as an indicator of cardiac performance. The effects of EE₂ exposure, as well as, its interactions with other steroid hormones, on cardiac performance will be discussed.

Lastly, physiological sex differences in juveniles are often assumed to be non-existent, causing sex to not be included as a variable during the design and analysis of experiments. However, in both our present and previous studies we have found differences between the sexes in immature rainbow trout of non-reproductive functions.  To this end, we will also discuss the importance of including sex as a variable regardless of life stage.