Nonuniform enhancement of baroreflex sensitivity by atrial natriuretic peptide in conscious rats and dogs

The influence of atrial natriuretic peptide (ANP) on the blood pressure (BP)-heart rate (HR) baroreflex was studied in conscious chronically instrumented dogs and rats. In both species, sigmoid steady-state baroreflex curves were constructed from the baroreflex changes in HR to alternating slow injections of vasopressor and vasodepressor drugs. When this method was used in dogs, ANP caused a small but significant (P < 0.05) enhancement of the sensitivity (22 ± 10%) and curvature (26 ± 10%) of the baroreflex, which was without a change in HR range. In rats, ANP had no significant effect on any baroreflex parameter derived from steady-state curves. By contrast, in the same rats, fast reflex HR responses to rapid increases in BP (ramp) exposed a substantial (81 ± 21%) ANP-induced enhancement of baroreflex sensitivity. Contribution from arterial vs. nonarterial afferents to the baroreflex is not uniform between these two techniques (steady state reflects largely arterial baroreceptor input, ramp evokes a greater proportion of cardiopulmonary afferent activation). The present study demonstrated that baroreceptor HR reflex responses to ANP depend on the baroreflex techniques employed and probably exposed a selectivity by ANP for nonarterial baroreflex pathways.