title: Similar baroreflex bradycardic actions of atrial natriuretic peptide and B and C types of natriuretic peptides in conscious rats.
abstract: OBJECTIVE
  We have previously shown that atrial natriuretic peptide (ANP) modulates cardiac barosensitive afferent pathways to enhance reflex bradycardia in rats. The present study examined whether B-type natriuretic peptide (BNP) and C-type natriuretic peptide (CNP) also modulate heart rate reflex function.
  
  
  METHODS
  Baroreflex bradycardia was evoked by rapid (over 4-6 s) intravenous (i.v.) infusions of methoxamine (100 microg/kg; 'ramp' baroreflex technique) in the presence of infused i.v. natriuretic peptide and of vehicle (0.9% saline, 270 microl/h) in conscious adult Munich-Wistar rats. Initially a dose-response study to ANP (infused at 25, 50 and 100 pmol/kg per min i.v.) was performed in 10 rats to determine an appropriate dose for subsequent experiments with the other peptides. In a separate group of 11 animals, rat BNP-32 and rat CNP-22 were infused at 50 pmol/kg per min i.v.
  
  
  RESULTS
  Reflex responses to ANP were dose-related, with a significant increase in baroreflex sensitivity of 50+/-15% at the 25 pmol dose, 102+/-10% at the 50 pmol dose and 117+/-11% at 100 pmol dose (all P<0.05). BNP and CNP (50 pmol/kg/min i.v.) substantially increased baroreflex bradycardia (by 115+/-17% and 62+/-15%, respectively; P<0.05) compared to vehicle infusion.
  
  
  CONCLUSIONS
  Both BNP and CNP augmented baroreflex slowing of heart rate in response to rapid increases in blood pressure in rats. Whereas other reports have shown marked differences in cardiovascular responses between the natriuretic peptides, particularly with CNP, our findings demonstrate an important common action of ANP, BNP and CNP to facilitate vagal heart rate baroreflexes.
authors.affiliation: Howard Florey Institute of Experimental Physiology and Medicine, University of Melbourne, Parkville, Australia.
authors.forename: C J
authors.initials: CJ
authors.lastname: Thomas
authors.forename: G A
authors.initials: GA
authors.lastname: Head
authors.forename: R L
authors.initials: RL
authors.lastname: Woods
mesh_terms: D000818:Animals; D009320:Atrial Natriuretic Factor / Q000494:pharmacology*; D017704:Baroreflex / Q000187:drug effects*; D001794:Blood Pressure / Q000187:drug effects; D001919:Bradycardia / Q000139:chemically induced / Q000503:physiopathology*; D002317:Cardiovascular Agents / Q000494:pharmacology*; D003243:Consciousness / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D006339:Heart Rate / Q000187:drug effects; D007262:Infusions, Intravenous; D020097:Natriuretic Peptide, Brain; D020098:Natriuretic Peptide, C-Type / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar
chemical_list: D002317:Cardiovascular Agents; D020097:Natriuretic Peptide, Brain; D020098:Natriuretic Peptide, C-Type; D009320:Atrial Natriuretic Factor