Patterns of sodium excretion during sympathetic nervous system arousal

The purpose of this study was to examine Na⁺ handling and regulation during 1 hour of behaviorally induced sympathetic nervous system (SNS) arousal followed by 2 hours of recovery. Two patterns of response were observed among experimental subjects, despite similar changes in blood pressure and heart rate. In one group (n=19), Na⁺ excretion increased significantly during SNS arousal, which then decreased significantly during recovery (12.3 versus 16.0 versus 13.1 meq/hr, baseline, SNS arousal, recovery, respectively). Changes in Na⁺ excretion were correlated with changes in creatinine clearance from baseline to SNS arousal (r=0.54) and SNS arousal to recovery (r=0.58), and were accompanied by significant increases in plasma renin activity (1.5 versus 2.0 ng/ml/hr) and aldosterone (8.5 versus 10.3 ng/ml/hr) from baseline to SNS arousal. Na⁺ excretion decreased during SNS arousal in the other group of subjects (n=17) and remained below baseline levels during recovery (16.2 versus 12.7 versus 11.9 meq/hr). These changes were associated with significant decreases in creatinine clearance from baseline to recovery (138 versus 121 ml/min/1.73 m²) and significant increases in plasma renin activity from baseline to SNS arousal (1.3 versus 2.2 ng/ml/hr) but not in aldosterone. Control subjects (n=24) maintained baseline levels of each variable throughout the procedure These results suggest that individuals differ in Na⁺ handling and regulation during behavioral arousal. Decreases in Na⁺ have been reported previously in humans and animals at risk for the development of hypertension.