The effects of atrial pacing and ballooning on the plasma concentration of atrial natriuretic peptide in anesthetized dogs with or without vagotomy.

To study the mechanisms of release of atrial natriuretic peptide (ANP), the plasma concentration of ANP, atrial pressure and urinary sodium excretion were determined in anesthetized dogs during balloon inflation in the left atrium or during rapid atrial pacing. The effects of bilateral cervical vagotomy on these variables were also examined. Balloon inflation which elevated the left atrial pressure by more than 4 mmHg increased the plasma concentration of ANP (+40%, p less than 0.05). This increase in ANP concentration was not altered by vagotomy. Rapid atrial pacing at rates of more than 160 beats/min also significantly increased the left atrial pressure (+2.3 mmHg, p less than 0.02), urinary sodium excretion (+45%, p less than 0.05) and plasma concentration of ANP (+130%, p less than 0.05). Vagotomy did not affect these changes. The degree of the increase in plasma ANP concentration was significantly greater during rapid atrial pacing than during intraatrial ballooning. These results suggest that the release of ANP is stimulated in part by elevating the left atrial pressure and in part by increasing the frequency of atrial contractions and that the increase in the plasma ANP concentration is possibly involved in the so-called atrial natriuresis. Furthermore, the release of ANP was proven to be independent of the vagal nerve reflex.