Atrial natriuretic factor (ANF 103–126) enhances volume- and pressor-induced heart rate response in the conscious rat

The reduction in blood pressure due to ANF(103–126) fails to elicit reflex cardioacceleration in the conscious rat. To examine baroreflex sensitivity, the effect of ANF(103–126) on the heart period (HP) response to rapid central volume expansion and to alterations in mean arterial pressure (MAP) induced by bolus injections of phenylephrine and sodium nitroprusside was assessed. ANF(103–126) significantly augmented the bradycardic response induced by acute volume expansion from 426 ± 21 to 391 ± 23 beats min^-1 versus 421 ± 23 to 405 ± 24 without ANF(103–126). Baroreflex sensitivity was defined by the ratio of the change in heart period to the maximal change in mean arterial pressure. The dose of ANF(103–126) utilized did not affect basal heart rate or the magnitude of the mean arterial pressure response to phenylephrine but did significantly enhance the nitroprusside-induced decrease in mean arterial pressure. Baroreceptor sensitivity to phenylephrine was significantly increased by ANF(103–126): 0.997 ± 0.07 (ms mmHg^-1) during ANF(103–126) vs 0.613 ± 0.08 during vehicle. The total duration of the heart rate response to phenylephrine was also prolonged. In contrast, ANF(103–126) did not alter the baroreceptor sensitivity (1.45 ± 0.3 vs 1.43 ± 0.2 ms mmHg^-1) or duration of heart rate response to nitroprusside. In the conscious rat, ANF(103–126) modifies the heart rate response to changes in mean arterial pressure and acute central volume expansion. This action appears to be dependent on stimulation of cardiac vagal afferents.