Relationship between renin and extracellular fluid volume in normotensive and hypertensive subjects

Plasma renin activity and extracellular fluid volume were determined in 34 normotensive and in 35 sustained essential hypertensive patients with normal renal function, balanced sodium intake and urinary output. In normotensives, plasma renin activity was negatively correlated to extracellular fluid volume (r = 0.54; p = 0.001). The 95% confidence limits of the normotensive curve was used as nomogram to classify the hypertensive patients into two groups: those (23 cases) that fell within the limits of the normal curve (group I) and those (12 cases) that were below these limits (group II). In comparison with group I, group II was characterized by: (i) similar values for age, blood pressure, inulin clearance and extracellular fluid volume and (ii) significantly but lower values (p less than 0.001) for plasma renin activity with maintenance of the relationship between extracellular fluid volume and renin. The study strongly suggests that (i) the hypertensives of group I had no abnormal regulation of the renin-angiotensin system in comparison with the control subjects and (ii) the hypertensives of group II had an extracellular fluid volume-renin relationship set for lower values of renin.