Influence of Atrial Natriuretic Factor on Spontaneous Baroreflex Sensitivity for Heart Rate in Humans

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Abstract
Abstract Our objective in these experiments was to evaluate the effects of atrial natriuretic factor on the gain of the spontaneous baroreceptor–heart rate reflex in humans. On two separate study days, we gave either atrial natriuretic factor during supine rest (16 nmol over 3 minutes, then 16 pmol/kg per minute) or saline (as vehicle) to nine healthy men (age, 23±1 years; mean±SEM) according to a random, double-blind design. Beat-by-beat RR interval and systolic pressure were recorded noninvasively. Sequences during which systolic pressure and the RR interval of the following beat changed in parallel (either increasing [Up] or decreasing [Down]) over at least three consecutive beats were identified and classified as baroreceptor–heart rate reflex sequences. Regression lines relating RR interval to the preceding systolic pressure were derived for each individual sequence. The mean value of the slopes of these regression lines was calculated to obtain the mean spontaneous baroreflex sensitivity for heart rate for each subject. Saline infusion did not change RR interval, systolic pressure, or number of baroreflex sequences nor the slope of the mean spontaneous baroreflex sensitivity for heart rate or slopes of Up or Down sequences. Atrial natriuretic factor, at a dose that lowers central venous pressure, did not affect systolic pressure, respiratory rate, or the number of baroreflex sequences but reduced RR interval from 952±35 to 930±40 ms ( P <.04) and the mean slope of spontaneous baroreflex sensitivity for heart rate from 32.7±4.8 to 23.1±2.8 ms · mm Hg −1 ( P <.04). Baroreflex sensitivity during Up sequences decreased during atrial natriuretic factor infusion, from 32.9±5.5 to 24.2±3.3 ms · mm Hg −1 ( P <.05). The slope of Down sequences did not change (from 27.9±4.2 to 23.0±3.2 ms · mm Hg −1 ) compared with baseline values, but when compared with the slope during saline infusion (35.0±5.2 ms · mm Hg −1 ), this effect of atrial natriuretic factor on baroreflex sensitivity during Down sequences was significant ( P <.05). These data indicate that atrial natriuretic factor reduces the vagal component of the arterial baroreflex control of heart rate in healthy humans. The cardioacceleration observed in humans during atrial natriuretic factor infusion may be in part due to diminished parasympathetic modulation of heart rate.