Differential expression of the corticosteroid receptors GR1, GR2 and MR in rainbow trout organs with slow release cortisol implants

Abstract

The present study describes the transcriptional levels of the corticosteroid receptors (CRs) GR1, GR2 and MR in the different organs of the rainbow trout (Oncorhynchus mykiss) in response to a slow release of cortisol, throughout a 10-day period. We show that after short term (1 day after cortisol implantation), when the plasma levels of cortisol emulate an acute stress, the GR2 and MR expression levels were upregulated in the brain and head kidney tissues. This result reflects the role of these organs as regulators of the stress response. In general, the rest of the organs, especially gills, intestine, liver, muscle and spleen, showed decreased transcriptional levels of GR1, GR2 and MR, along with the highest plasma cortisol levels. At day 5 after cortisol implantation, when cortisol levels emulate a chronic stress, the most affected organs were gills and skin, where an upregulation of the CRs was found. In the recovery period, when cortisol levels were basal (day 10), we still found changes in the transcriptional levels of the CRs in gills, spleen and gonads. The cortisol increase at days 1 and 5 after implantation is accompanied by high plasma glucose concentrations, supporting the role of cortisol on carbohydrate metabolism. However, after 10days of implantation, glucose returned to control levels suggesting a trade-off on the steady state of the metabolic function. We also observed increased hematocrit and hemoglobin at day 1, indicating a cortisol-induced higher metabolic demand involving an increase in oxygen transport efficiency. Our results demonstrate that increased plasma cortisol induced by a slow-release implant of cortisol mimics the overall effects of stress and affects the expression of the three CRs, generating different transcriptional patterns in a time- and organ-specific manner.