The effect of sodium depletion on plasma norepinephrine kinetics in patients with essential hypertension

The effects of sodium depletion on plasma norepinephrine (NE) kinetics were studied in 14 patients with essential hypertension using the steady state NE infusion technique on the theoretical basis of a two-compartmental open model. The calculated half time of rapid removal phase (t 1/2 alpha) of plasma NE was significantly delayed in the hypertensives (1.20 +/- 0.22 min, mean +/- SD) than in normal subjects (0.89 +/- 0.14) (p less than 0.01). The total clearance rates were comparable between the 2 groups (47 +/- 7 vs 48 +/- 11 ml/kg/min). The rates of the endogenous NE outflow into the circulation (RE-NE) were not significantly different between normal (5.29 +/- 1.68 ng/kg/min) and hypertensives (7.69 +/- 5.42), although 5 hypertensive patients (36%) showed an increased RE-NE above the normal range. The prolonged half time (t 1/2 alpha) in the hypertensives tended to be shortened after sodium depletion induced by either low sodium diet or diuretics (1.04 +/- 0.22, p less than 0.001). Both plasma NE and RE-NE were significantly increased after sodium depletion. A close correlation was observed between plasma NE and RE-NE (r = 0.907, p less than 0.001) in these subjects. These results suggest the slowed neuronal uptake of NE at the sympathetic nerve terminals in some patients with essential hypertension, occurring in part as a sodium-mediated consequence.