Ambient salinity-dependent effects of homologous natriuretic peptides (ANP, VNP, and CNP) on plasma cortisol level in the eel.
The effects of three eel natriuretic peptides (NPs), i.e., ANP, VNP, and CNP on plasma cortisol levels were investigated in conscious freshwater (FW)- and seawater (SW)-adapted eels with permanent arterial catheter. The experiment was performed between 9:00 and 15:00 of the day, when the natural plasma cortisol level was relatively stable. After a single intra-arterial injection of ANP, VNP, or CNP at 100 pmol/kg, only CNP, but not ANP or VNP, increased plasma cortisol concentration in FW eels. In SW eels, however, only ANP at the same dose increased plasma cortisol concentration. The effect of CNP in FW eels and that of ANP in SW eels were dose-dependent between 10 and 1000 pmol/kg. On the other hand, ANP and VNP were equally effective, but CNP was ineffective, in increasing hematocrit in both FW and SW eels. These results show that the effect of NPs on plasma cortisol level is dependent on the ambient salinity in the eel. Since cortisol plays a pivotal role in environmental adaptation of fishes, the results suggest a possible involvement of ANP and CNP in the adaptation to SW and FW, respectively. Furthermore, this is the first evidence showing that ANP and VNP exert different effects in fish despite they share the same receptor, NPR-A.
Li
Yuan-You
YY
Laboratory of Physiology, Department of Marine Bioscience, Ocean Research Institute, University of Tokyo, 1-15-1 Minamidai, Nakano, Tokyo 164-8639, Japan.
Takei
Yoshio
Y
D000222:Adaptation, Physiological; D000818:Animals; D009320:Atrial Natriuretic Factor / Q000097:blood*; D002940:Circadian Rhythm; D004305:Dose-Response Relationship, Drug; D004524:Eels / Q000097:blood*; D005618:Fresh Water; D006400:Hematocrit; D006854:Hydrocortisone / Q000097:blood*; D007124:Immunoenzyme Techniques; D020098:Natriuretic Peptide, C-Type / Q000097:blood*; D012623:Seawater / Q000737:chemistry; D014882:Water-Electrolyte Balance / Q000502:physiology*
D020098:Natriuretic Peptide, C-Type; C068986:ventricular natriuretic peptide, eel; D009320:Atrial Natriuretic Factor; D006854:Hydrocortisone