Effect of rapid intra-atrial saline infusion on atrial pressures and atrial natriuretic hormone secretion

To evaluate the relationship between the right atrial pressure and atrial natriuretic hormone secretion, we studied 16 healthy males, ages 18-24, after five days on a low-salt diet (mean 24-h urinary sodium excretion: 17 +/- 3 mEq). After 90 min of equilibration to the supine position, a multilumen catheter was inserted into the right atrium, and 11 of isotonic saline was infused intra-atrially over 15 min through this catheter. Blood pressure, heart rate, and right atrial pressure were recorded just before (0 min), immediately after completion of the infusion (15 min), and every 15 min for 45 min thereafter. Two blood samples were drawn at each time point for atrial natriuretic hormone assay: one from the right atrium (central) and the other from a peripheral vein. Blood pressure did not change significantly during the entire study. Heart rate increased by 5 beats/min on average at 15 min (p < 0.005) and returned to baseline at 60 min. Good correlation occurred between central and peripheral atrial natriuretic hormone levels at times 0, 30, 45 and 60 min (r2 = 0.66, 0.45, 0.76 and 0.70, respectively; p < or = 0.02). An increase in right atrial pressure and an increase in central atrial natriuretic hormone levels correlated well at times 30, 45 and 60 min, but there was no such correlation between an increase in right atrial pressure and an increase in peripheral atrial natriuretic hormone levels at any time point. Similarly, a maximum increase in right atrial pressure correlated with a maximum increase in central atrial natriuretic hormone levels (r2 = 0.48; p < 0.02), but not with a maximum increase in peripheral levels of this hormone. We concluded that an increase in right atrial pressure caused by a rapid infusion of isotonic saline induces secretion of atrial natriuretic hormone in the right atrium. The observed discrepant course of change in central and peripheral atrial natriuretic hormone levels suggests the additional contribution of secretion beyond the level of the coronary sinus.