Reproductive Stage Impacts Interrenal Tissue Function in Rainbow Trout, Oncorhynchus mykiss

This research investigates if reproductive stage impacts the sensitivity of an animal to a stressor. In general, the initial phases of ovarian development are initiated and maintained by 17β-estradiol (see review; Scott, 1987).  During this period there is massive growth and development of the oocytes in fishes. Then, a maturation-inducing hormone (e.g., progestagen), regulates the later phases of development through ovulation. We utilized these two hormonal hallmarks (17β-estradiol and 17α-20β-dihydroxy-3-one [DHP]) to mimic their respective reproductive stage in an in vitro incubation of head kidney tissue.  The objective was to investigate if cortisol production to a standardized stressor is altered during these different reproductive phases. The treatment groups were adrenocorticotropic hormone (ACTH) , DHP, 17β-estradiol, ACTH/DHP, and ACTH/17β-estradiol. Cortisol levels in the media were quantified using an ELISA and various mRNA transcripts in the head kidney that are involved in steroidogenesis and related paracrine mechanisms were quantified with qPCR.  Our preliminary analysis indicated there is a significant difference among treatments, 17β-estradiol does not appear to impact cortisol synthesis, but DHP appears to increase the interrenal’s sensitivity to ACTH or ability to synthesize cortisol.  Collectively, these data suggest that the reproductive stage does impact the animal’s ability to respond to stressors.