Impaired atrial receptor modulation or renal nerve activity in dogs with chronic volume overload1

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Abstract
Left atrial receptors with vagal afferents are reset and become less sensitive in dogs with chronic high output congestive heart failure (Zucker et al J Clin Invst 1977;60:323). We determined if the normal reflex inhibition of renal sympathetic nerve activity (RNA) which occurs in response to left atrial distension is altered in dogs with chronic volume overload produced by an aorto-vena caval fistula (AVF). In addition, we examined the ability of the arterial baroreflex to alter RNA. In normal dogs, left atrial distension decreased RNA by 6.8±1.8% per mmHg change in left atrial pressure (LAP). After carotid sinus denervation (CSD), this inhibition was increased to 10.9±1.4% per mmHg change in RNA in response to left atrial distension. Vagotomy completely abolished any change in RNA in response to left atrial distension. In contrast, dogs with chronic AVF's demonstrated an increase in RNA in response to left atrial distension by 4.5 ±3.9% per mmHg change in LAP. The response of the AVF dogs was significantly different from the normal dogs (p<0.005). This was also the case after CSD. Loading and unloading of the arterial baroreceptors with norepinephrine and nitroprusside demonstrated that the modulation of RNA by arterial baroreceptors was similar in AVF dogs compared with normal dogs. The present study demonstrates that chronic volume overload results in a decrease in the peripheral sympathetic inhibitory effects of left atrial receptor stimulation at a time when arterial baroreceptor function is preserved.