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COMPARATIVE AND EVOLUTIONARY PHYSIOLOGY

Responses of the trout cardiac natriuretic peptide system to manipulation of salt and water balance

¹University of Notre Dame-Department of Biological Sciences, Notre Dame, Indiana; and ²Indiana University School of Medicine-South Bend, South Bend, Indiana

Submitted 31 October 2008 ; accepted in final form 20 January 2009

Natriuretic peptides (NPs) are evolutionarily conserved hormones that affect blood pressure and fluid volume through membrane-bound guanylate cyclase (GC)-linked natriuretic peptide receptors-A and -B (NPR-A and NPR-B, respectively) in a variety of vascular, renal, and other tissues. The principal physiological stimulus for cardiac NPs in fish is somewhat debated between two prominent theories: regulation of salt balance (osmoregulatory hypothesis) or prevention of volume expansion (cardioprotective hypothesis). In the present study, we examined atrial and ventricular expression of trout NPs, atrial (ANP), brain (BNP), and ventricular (VNP) using Northern (mRNA), Western (NP pro-hormone), and qPCR (GC-NPR-A and -B mRNA) blot analysis following independent manipulation of plasma salt and volume levels after chronic exposure to freshwater (FW; volume loaded, salt depleted), saltwater (SW; volume depleted, salt loaded), or freshwater trout fed a high-salt diet (FW-HSD; volume and salt loaded). We also measured NP transcriptional response to acute (2 h) volume expansion with dialyzed plasma (VE; 80% blood vol) or volume depletion by hemorrhage (VD, 20% blood volume every 30 min for 2 h) with real-time PCR. In essentially all instances, increased expression of the NP system was associated with FW-HSD or plasma expansion. There were no differences in NP expression between chronically adapted FW and SW fish, and hemorrhage decreased atrial ANP and VNP mRNA. These results indicate that rainbow trout cardiac NPs and cardiovascular GC-NPRs respond principally to volume, not salt overload, and this suggests that the primary function of trout cardiac NP system is to protect the heart.

natriuretic peptide receptors; hypervolemia; hypervolemia; osmoregulation; cardioprotection

This article has been cited by other articles:

				K. R. Johnson and K. R. Olson The response of non-traditional natriuretic peptide production sites to salt and water manipulations in the rainbow trout J. Exp. Biol., September 15, 2009; 212(18): 2991 - 2997. [Abstract] [Full Text] [PDF]