Influence of cortisol on osmoregulation and energy metabolism in gilthead seabream Sparus aurata

Gilthead seabream Sparus aurata were injected intraperitoneally with slow-release implants of coconut oil alone or containing cortisol (50 and 100 microg x g(-1) body weight), and sampled after two, five, and seven days to assess the simultaneous effects of cortisol on both osmoregulation and energy metabolism. Plasma cortisol levels increased in treated fish to 50-70 ng x ml(-1). An enhanced hypoosmoregulatory capacity of cortisol-implanted fish is suggested by the increase observed in gill Na+, K+-ATPase activity, and the decrease observed in plasma ion concentration (Na+ and Cl-) and osmolality. Cortisol also elicited metabolic changes in liver (increased gluconeogenic potential suggested by elevated FBPase activity, and decreased potential of glycolysis and pentose-phosphate shunt, suggested by the decreased activities of both PK and G6PDH) supporting changes in levels of plasma metabolites suitable for use in other tissues. Thus in this study, we demonstrate for the first time in fish that cortisol treatments elicit changes in the use of exogenous glucose in gills (decreased HK activity) and an increased glycolytic and glycogenic potential in brain (increased GPase, PK and PFK activities).