Similar baroreflex bradycardic actions of atrial natriuretic peptide and Band C types of natriuretic peptides in conscious rats

Objective We have previously shown that atrial natriuretic peptide (ANP) mo dulates cardiac barosensitive afferent pathways to enhance reflex bradycard ia in rats. The present study examined whether B-type natriuretic peptide ( BNP) and C-type natriuretic peptide (CNP) also modulate heart rate reflex f unction. Design Baroreflex bradycardia was evoked by rapid (over 4-6 s) intravenous (i.v.) infusions of methoxamine (100 mu g/kg; 'ramp' baroreflex technique) in the presence of infused i.v. natriuretic peptide and of vehicle (0.9% sa line, 270 mu l/h) in conscious adult Munich-Wistar rats. initially a dose-r esponse study to ANP (infused at 25, 50 and 100 pmol/kg per min i.v.) was p erformed in 10 rats to determine an appropriate dose for subsequent experim ents 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 incre ase 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 bradycardi a (by 115 +/- 17% and 62 +/- 15%, respectively; P < 0.05) compared to vehic le infusion. Conclusions Both BNP and CNP augmented baroreflex slowing of heart rate in response to rapid increases in blood pressure in rats. Whereas other report s have shown marked differences in cardiovascular responses between the nat riuretic peptides, particularly with CNP, our findings demonstrate an impor tant common action of ANP, BNP and CNP to facilitate vagal heart rate baror eflexes. J Hypertens 1999, 17:801-806 (C) Lippincott Williams & Wilkins.