Plasma and urinary norepinephrine values at extremes of sodium intake in normal man.

SUMMARY To examine the effects of a wide range of sodium intake on plasma and urinary norepinephrine values in normal man, we studied 14 men at six levels of sodium intake from 10 to 1500 mEq/24 hrs. Mean blood pressure increased from 83.8 ± 1 (SEM) to 1003 ± 3 mm Hg, while cardiac index increased from 2.6 ± 0.1 to 3.6 ± 0 3 llters/min/m1 (p < 0.001). Upright venous plasma norepinephrine concentration decreased from 467 ± 6 3 to 67 ± 24 pg/ml, while urinary norepinephrine excretion decreased from 543 ± 3.4 to 23.4 ± 2.9 Mg/24 hrs. There was no effect of sodium intake on blood pressure responses to isometric hand-grip contraction. The urinary sodium excretion was inversely correlated with urinary norepinephrine excretion (r = − 0.46, p < 0.001). There was a significant inverse multiple correlation of mean blood pressure and plasma and urinary norepinephrine values (correlation coefficient = 0.72, p < 0.001). These results indicate that sodium homeostasis has a signiflcant effect on plasma and urinary norepinephrine values. Sympathetic nervous system activity appears to decrease with sodium loading in normal subjects. These responses may have facilitated the excretion of massive salt loads in normal subjects and may nave modulated the increases in blood pressure.