High-NaCl diet reduces cardiac vagal afferent nerve response to volume expansion.

To localize the mechanism by which high dietary NaCl intake decreases the reflex inhibitory effects of intravenous volume expansion on efferent renal sympathetic nerve activity, experiments were performed in anesthetized normal rats prepared for separate examination of the afferent and efferent limbs of the cardiopulmonary baroreceptor reflex. When left ventricular end-diastolic pressure, an index of left heart filling pressure, was progressively increased by intravenous isotonic saline administration in sinoaortic-denervated rats, the increase in cardiac vagal afferent nerve activity was less in rats consuming high compared with normal dietary NaCl intake. During electrical stimulation of the central vagus nerve in sinoaortic-denervated rats, the decreases in efferent renal sympathetic nerve activity were similar in rats consuming high and normal dietary NaCl intake. Thus the effect of high dietary NaCl intake to decrease overall cardiopulmonary baroreceptor reflex gain during intravenous volume expansion is located in the afferent limb of the reflex arc.