EFFECTS OF EXOGENOUS CORTISOL ON THE EXPRESSION OF CORTISOL AND NATRIURETIC PEPTIDE B RECEPTORS MRNA IN GILL EPITHELIA OF JAPANESE EELS, ANGUILLA JAPONICA.

Cortisol, a major corticosteroid factor secreted by the interrenal gland, has been proven to be important in hypo-osmoregulation in teleost fish (Mayer et al., 1967). In the initial phase of seawater acclimation, a marked transitory increase in plasma cortisol levels was detected. The duration of the elevated plasma cortisol level was correlated with morphological changes in the gill epithelium, whereby a drastic cellular and functional reorganization occurred to adjust to this short-term osmotic crisis. Considerable numbers of studies have demonstrated that exogenous cortisol treatment stimulated Na+/K+-ATPase activities, mitochondria content and cellular differentiation of both freshwater and seawater CC. Nevertheless, the extent of cell proliferation and differentiation as well as the biochemical changes in cortisol treated freshwater fish were significantly lower than that of seawater fish (Wong and Chan, 2001). This could be explained as seawater acclimation is controlled by a complex endocrine regulatory mechanism in mediating the whole course of adaptation. Therefore informatio