GARCIA, M.; HINKLE, L.; VEILLETTE, P.A.; SPECKER, J.L.; University of Rhode Island; University of Rhode Island; University of Rhode Island; University of Rhode Island: Effect of exogenous cortisol and RU486 on cortisol concentrations and on Na⁺/K⁺-ATPase and glucocorticoid-like receptor immunoreactivity in juvenile summer flounder

Cortisol is a steroid hormone secreted in response to stress and known to be a seawater-adapting hormone in teleost fishes. RU486 is a synthetic glucocorticoid and progesterone receptor blocker. Our aim was to quantify the effects of exogenous cortisol and RU486, alone or together, on whole-body cortisol concentrations and to localize glucocorticoid-like receptor (GLR) and Na⁺/K⁺-ATPase using immunocytochemistry in juvenile summer flounder, which are marine teleosts and were held at 30 ppt. Flounder were immersed in cortisol (20 mM), RU486 (0.12 mM), cortisol and RU486, or the vehicle alone (control) for 5 days. Immersion in RU486, with or without cortisol, significantly elevated whole-body concentrations of cortisol, confirming uptake by indicating suppression of the negative feedback loop on the cortisol axis. Immunoreactive-GLR and Na⁺/K⁺-ATPase were evident in all treatment groups in the primary osmoregulatory tissues (gill, intestine, and kidney). The GLR was more cytoplasmic in the intestine of RU486-treated flounder, whereas in control and cortisol-treated flounder nuclear staining was more evident. Localization of the GLR in the intestine and gills further evidences a direct action of cortisol on the major osmoregulatory organs. The present study also adds to the ability to manipulate the cortisol axis and therefore to understand cortisol�s role. [Supported by an REU Supplement to NSF IBN-0220196]