Abnormal relation of extracellular fluid volume and exchangeable sodium with systemic arterial pressure in early borderline essential hypertension

Abstract

Interrelations between systemic arterial pressure, extracellular fluid (ECF) volume, exchangeable sodium (Na) and the renin-angiotensin-aldosterone system were studied in 38 young patients with borderline hypertension and in 37 age- and sex-matched control subjects. ECF volume and exchangeable Na were subnormal (not significant) in borderline hypertension. In normal subjects, volume data did not relate to arterial pressure; in contrast, negative correlations were observed between arterial pressure and ECF volume or exchangeable Na in patients with borderline hypertension (in hypertensive women, r greater than or equal to 0.7, p less than 0.01). Plasma renin activity was consistently elevated in borderline hypertension, mainly in the upright posture, and these values were inversely correlated with ECF volume and exchangeable Na. No correlation was observed between arterial pressure and plasma renin activity. These results show that slight elevation of arterial pressure in the early stage of hypertension induces a proportional decrease in ECF volume, suggesting that the phenomenon of pressure-natriuresis is operative in young borderline hypertensive persons. The renin-angiotensin system is activated in these patients, in part to preserve sodium homeostasis.