Mechanism of diuretic response associated with atrial tachycardia

Left atrial pacing was performed in three groups of anesthetized dogs. In the first group of eight intact dogs a mean increase in atrial rate (AR) from 140 +/- 7 to 244 +/- 6 was associated with a decrease in urinary osmolality (U osmol) from 631 +/- 72 to 264 +/- 43 mosmol/kg (P less than .001), and free-water clearance (CH20) increased from -.325 +/- .06 to +.355 +/- .15 ml/min (P less than .001). At the same time left atrial pressure (LAP) increased from 6 +/- 1 to 15 +/- 1 mmHg (P less than .001). A second group of studies was performed in six hypophysectomized, steroid-replaced animals receiving 40-50 muU/kg per min of antidiuretic hormone (ADH). In these animals AR was increased from 148 +/- 17 to 250 +/- 17 but diuresis did not occur. In these studies Uosmol was 690 +/- 55 before and 704 +/- 49 mosmol/kg after atrial pacing and CH20 also did not change. Left atrial pressure increased from 10 +/- 2 to 19 +/- 2 mmHg during atrial pacing. A third group of studies was performed in five animals with bilateral cervical vagotomy. In these animals AR was increased from 159 +/- 6 to 258 +/- 17 and LAP increased from 7 +/- 1 to 16 +/- 2 mmHg. Osmolality increased from 808 +/- 72 to 1,049 +/- 65 musmol/kg (P less than .005) and CH20 was unchanged. These results, therefore, indicate that atrial tachycardia primarily increases renal water excretion by suppressing ADH release. This reflex is dependent on the integrity of cervical vagal pathways.