Sodium excretion and sympathetic activity in relation to severity of hypertensive disease

The relationship between the severity of hypertensive disease and sodium excretion and sympathetic activity has been studied in subjects of the same age and sex derived from screening a total population. 19 untreated subjects with casual blood-pressure (B.P.) above 175/115 mm Hg on two separate occasions made up the hypertensive group. A normotensive group (n =19) was obtained by selecting a 5% random sample from all subjects with casual B.P. below 160/95. Sympathetic activity was determined from noradrenaline excretion and the severity of hypertension assessed by recording resting diastolic B.P., signs of left ventricular hypertrophy on orthogonal E.C.G., and the glomerular filtration-rate. In the hypertensive group the resting B.P. correlated well both with signs of left ventricular hypertrophy and with the glomerular filtration-rate--i.e., the degree of severity of the hypertension. Up to the level of 90 mm Hg resting diastolic B.P., sodium excretion rose in complete agreement with the theory of pressure diuresis. Above 90 mm Hg, however, sodium and noradrenaline excretion fell with increase of B.P. These two findings indicated that with increasing severity of hypertension the sodium balance overrides the sympathetic activity in the long-term regulation of B.P. This may have both prognostic and therapeutic implications.