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

Keven R. Johnson, Kenneth Olson

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19 Citations (Scopus)

Abstract

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.

Original languageEnglish
JournalAmerican Journal of Physiology - Regulatory Integrative and Comparative Physiology
Volume296
Issue number4
DOIs
StatePublished - Apr 2009

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Natriuretic Peptides
Trout
Salts
Water
Guanylate Cyclase
Atrial Natriuretic Factor
Fresh Water
Messenger RNA
Fishes
Hemorrhage
Plasma Volume
Oncorhynchus mykiss
Blood Volume
Blood Vessels
Real-Time Polymerase Chain Reaction
Hormones
Diet
Blood Pressure
Kidney
Membranes

Keywords

  • Cardioprotection
  • Hypervolemia
  • Natriuretic peptide receptors
  • Osmoregulation

ASJC Scopus subject areas

  • Physiology
  • Physiology (medical)

Cite this

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abstract = "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.",
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AB - 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.

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