The impact of acute PAH exposure on the toadfish glucocorticoid stress response

The objective of the present study was to determine whether the polycyclic aromatic hydrocarbons (PAHs) associated with the Deepwater Horizon (DWH) oil spill impacted the stress response of teleost fish. The hypothesis was that intraperitoneal (IP) treatment with PAHs associated with the DWH oil spill or waterborne exposure to DWH oil high energy water-accommodated fraction (HEWAF) would result in the downregulation of the stress response of Gulf toadfish, Opsanus beta, a benthic marine teleost fish that resides in the Gulf of Mexico. In vivo plasma cortisol levels and adrenocorticotropic hormone (ACTH)-mediated cortisol secretion by in vitro isolated kidney tissue were measured. Toadfish at rest IP-treated with naphthalene had higher plasma cortisol compared to fluorene-treated and control fish; phenanthrene-treated fish tended to have higher plasma cortisol levels that fluorene-treated and controls. When subjected to an additional crowding stress, naphthalene and phenanthrene-treated fish were no longer able to mount a stress response compared to fluorene-treated and control fish, suggesting exhaustion of the stress response. Supporting this in vivo data, there tended to be less cortisol released by the kidney in vitro from naphthalene and phenanthrene-treated fish in response to ACTH compared to controls. In contrast, toadfish at rest exposed to 3% Slick A HEWAF did not have significantly different plasma cortisol levels compared to controls. But, exposed fish did have significantly less cortisol released by the kidney in vitro in response to ACTH. When toadfish were subjected to an additional stress, there were no significant differences in plasma cortisol or ACTH, suggesting the action of a secondary secretagogue to maintain plasma cortisol in vivo. Combined, these data suggest that in response to acute PAH exposure, there may be internalization or downregulation of the melanocortin 2 receptor (MC2R) that mediates the action of ACTH.