Measurement of Plasma Cortisol Levels in the Eel Anguilla Anguilla in Relation to Osmotic Adjustments

Abstract

The competitive protein-binding radioassay (CPB method) of Murphy (1967) has been adapted to determine total cortisol levels in the plasma of the eel, Anguilla anguilla L. Validation of the method for this species depended in part on the development of a chromatographic\p=m-\fluorimetrictechnique for eel cortisol, following classical procedures and using radioactive tracers; by this means, the specificity of the CPB method for cortisol in eel plasma was established. Accuracy, precision and sensitivity of the CPB method were also investigated and were shown to be satisfactory.Plasma total cortisol levels were determined in eels during osmotic adjustments after transfers from fresh water (FW) to sea-water (SW) and vice versa, and from FW to distilled water. Plasma osmotic pressure and/or sodium levels were monitored simultaneously, to follow the progress of osmotic regulation. In only one of the transfer situations did the plasma cortisol level change significantly, showing a marked transitory increase during the first few days after transfer from FW to SW, corresponding to the development and correction of an 'osmotic crisis'. Plasma cortisol levels were the same in eels adapted for long periods to FW and to SW. Plasma cortisol fell to extremely low levels after hypophysectomy.These results are discussed in the light of the literature on hormonal control of osmoregulatory mechanisms in the eel, with particular emphasis on the role of adrenocorticosteroids in ionic regulation of animals in SW.

Effect of osmotic shrinkage and hormones on the expression of Na+/H+ exchanger-1,Na+/K+/2Cl– cotransporter and Na+/K+-ATPase in gill pavement cells of freshwater adapted Japanese eel,Anguilla japonica

“…During seawater transfer, it has been reported that there was a marked transitory increase in plasma cortisol and branchial cAMP levels (Foskett et al, 1983;Marshall and Singer, 2002;Assem and Hanke, 1981;Ball et al, 1971;Mayer et al, 1967). Numerous studies have demonstrated the stimulatory effect of cortisol on Na + /K + -ATPase and NKCC expressions in different fish species (Pelis and McCormick, 2001;Wong and Chan, 2001;LaizCarrion et al, 2003;Richards et al, 2003;Sunny and Oommen, 2001).…”

Activity of the pituitary gland in embryo and larval stages of coho salmon, Oncorhynchus kisutch

“…The ACTH-interrenal axis is generally thought to be involved in seawater osmo(iono)regulation in some adult teleosts (Chester Jones et al 1969;Ball et al 1971). In larval coho salmon the ACTH cells appear to differentiate and become functional a few days after hatching.…”

The Multifunctional Fish Gill: Dominant Site of Gas Exchange, Osmoregulation, Acid-Base Regulation, and Excretion of Nitrogenous Waste

“…Early plasma assays found that cortisol levels increased when fish were acclimated to seawater (11,20), but more recent studies have shown that cortisol concentrations also increase after transfer to fresh water in eel, tilapia, killifish, mullet, flounder, and sea bass (reviewed in Ref. 473), suggesting a role for cortisol in freshwater osmoregulation.…”