Cortisol promotes and integrates the osmotic competence of the organs in North African catfish (Clarias gariepinus Burchell): Evidence from in vivo and in situ approaches

The short-term in situ and long-term in vivo effects of cortisol were examined in North African catfish (Clarias gariepinus) to identify how this major corticosteroid integrates the osmotic competence of fish organs. In the in situ approach, the hydromineral effects of cortisol perfusion (75–300 ng ml−1) for 20 min were tested and the indices of hydromineral and metabolic regulations were measured in our in vivo experimental fish after three alternate intraperitoneal cortisol injections (40 and 200 ng g−1 body mass) for 5 days. Na+, K+-ATPase activity, a measure of cellular osmotic competence, responded to in situ and in vivo cortisol treatments. In situ cortisol delivery increased the Na+, K+-ATPase activity in the gill (P < 0.001) and kidney (P < 0.001) but decreased (P < 0.01) in the liver and showed no effect on intestine. In vivo cortisol treatment, on the contrary, increased Na+, K+-ATPase activity in the gills (P < 0.01), intestine (P < 0.05) and liver (P < 0.01) but decreased (P < 0.05) in the kidney. As expected, plasma cortisol increased (P < 0.001) with increasing doses of cortisol injections which produced direct effects on the metabolites and the mineral contents including the elevations of glucose (P < 0.05), lactate (P < 0.05) and Mg2+ (P < 0.05) and reductions of urea (P < 0.05), Na+ (P < 0.05) and K+ (P < 0.05) in the plasma. A decline of triiodothyronine (P < 0.01) occurred in the catfish after in vivo cortisol treatment and that implies a direct cortisol action on the homeostatic integration in this fish. Evidence is thus presented that in catfish cortisol regulates the whole body hydromineral and metabolite homeostasis by promoting and integrating the osmotic and metabolic functions of the multiple organ systems including liver.