Cortisol treatment improves the development of hypoosmoregulatory mechanisms in the euryhaline rainbow trout, Salmo gairdneri

Abstract

The effect of cortisol on osmoregulatory parameters was studied in rainbow trout, (Salmo gairdneri), kept in freshwater (FW) and/or transferred to seawater (SW). Repeated injections of 20 µg cortisol/g fish stimulated gill and gut Na(+)/K(+)-ATPase activity and reduced plasma Na(+) and Cl(-) levels after 2 weeks of treatment in FW-adapted fish. Cortisol doses of 0.05 and 1.0 µg/g were without effect. Repeated injections of 10 µg cortisol/g stimulated gill Na(+)/K(+)-ATPase activity and reduced plasma Na+ and Cl(-) levels in fish in FW, and significantly improved ion regulation after their transfer to 28SW. Higher doses of cortisol (10 and 20 µg/g) induced hyperglycemia, whereas low doses (0.05 and 1.0 µg/g were without effect or induced hypoglycemia. Plasma glucose levels decreased in cortisol-treated fish transferred to SW, whereas transient hyperglycemia was seen in the control fish.

Regulation of the glucocorticoid receptor mRNA levels in the gills of Atlantic salmon (Salmo salar) during smoltification

“…PRL is known to be a freshwater adapting hormone and hence should have an antagonistic action on salinity tolerance and inhibit the increase of gill Na + /K + ATPase activity. This type of effect following PRL treatment has been reported in Oncorhynchus species by Mc CORMICK et al (1991) andMADSEN andBERN (1992), but in Atlantic salmon, contradictory results were obtained by BOEUF et al (1994) who observed an increase of enzyme activity after PRL treatment.…”

“…It is still debated whether Cortisol is or not involved during smolting in the acquisition of a hypo-osmoregulatory capacity. Several authors suggest that Cortisol is regulating this hypo-osmoregulatory capacity, having stimulated Na + /K + ATPase activity and improved seawater adaptability in Pacific salmon species and in brown trout (RICHMAN and ZAUGG, 1987 ;Mc CORMICK and BERN, 1989 ;MADSEN, 1990). In addition, in Atlantic salmon, Mc CORMICK (1996) observed that Cortisol and GH had synergistic effects in stimulating gill Na + /K+ATPase activity and salinity tolerance.…”

Does the mineralocorticoid receptor have a functional role in the teleost gill?

“…Madsen (1990a) showed that Cortisol treatment directly improved the development of hypo-osmoregulatory ability in rainbow trout and that there was a synergistic interaction with GH in promoting chloride cell proliferation (Madsen, 1990b). The results from experimentally administered Cortisol treatment, however, are not consistent.…”

“…Complicating things further, Cortisol has been shown to be important for ion uptake and ion excretion and is considered by some to be a dual regulator of chloride cell differentiation and function (Kiilerich et al, 2007a). During smoking and acclimation to seawater, Cortisol has been shown to stimulate proliferation and differentiation of iontransporting chloride cells (Madsen, 1990a) and increase NKA enzyme activity in the gill to improve salinity tolerance (McCormick and Bern, 1989;Kiilerich et al, 2007a). Several studies focusing on increasing Cortisol levels in response to salinity levels and Cortisol treatments provide evidence that Cortisol has a considerable physiological impact on ion uptake (McCormick, 2001) and has been shown to synergistically interact with growth hormone (GH) to stimulate chloride cell proliferation (Madsen, 1990b).…”

“…The higher plasma Cortisol levels in the ion-poor group on day 1 and the saltwater group throughout the experiment may, therefore, serve an ionoregulatory role. Cortisol has been shown to enhance ionoregulation in salt water by stimulating cellular differentiation of chloride cells 29 (McCormick, 1990) and increase NKA activity (Madsen, 1990a;McCormick et al, 1991) in the gills of juvenile salmonids. Additionally, McCormick et al (1991) found that elevated…”