ATRIAL-PACING STIMULATES SECRETION OF ATRIAL NATRIURETIC POLYPEPTIDE WITHOUT ELEVATION OF ATRIAL PRESSURE IN AWAKE DOGS WITH EXPERIMENTAL COMPLETE ATRIOVENTRICULAR-BLOCK

To clarify whether or not tachycardia stimulates the secretion of atrial natriuretic polypeptide (ANP) without elevation of atrial pressure, we examined the effects of atrial pacing on ANP secretion in awake dogs with normal sinus rhythm and with complete atrioventricular block (CAVB), which was produced surgically by heat cauterization of His' bundle. In four dogs with normal sinus rhythm, atrial pacing increased the atrial rate from 146 ± 20 to 260 ± 10 beats/min, with marked elevation of right atrial pressure (from 0.2 ± 0.1 to 3.9 ± 0.8 mm Hg) and left atrial pressure (from 0.2 ± 0.1 to 8.6 ± 2.8 mm Hg). Along with the hemodynamic changes, the ANP level in plasma obtained from the coronary sinus was increased from 405 ± 99 to 849 ± 199 pg/ml (p < 0.01). In five dogs with CAVB, the ANP level was also significantly increased from 730 ± 82 to 1,137 ± 35 pg/ml (p < 0.01) by rapid atrial pacing (from 164 ± 20 to 317 ± 30 beats/min) in spite of the lack of any appreciable changes in either left or right atrial pressure. Furthermore, in the CAVB group, while the ventricular rate was increased by ventricular pacing from 52 ± 5 to 146 ± 16 beats/min, atrial pacing was performed simultaneously without atrioventricular (A-V) sequential form. Even under this condition, the ANP level was increased from 480 ± 172 to 626 ± 223 pg/ml (p < 0.05) without any substantial changes in atrial pressure. Such effects of rapid atrial pacing on ANP secretion were suppressed after infusion of autonomic blocking agents. These results demonstrate that atrial pacing per se stimulates ANP secretion from the heart without elevation of atrial pressure and indicate that this change is mediated by the autonomic nervous system.