The Correlation between Serum Angiotensin I-Converting Enzyme Activity and the Renin-Angiotensin-Aldosterone System in Hypertensive Patients

In order to investigate the role and origin of serum angiotensin I-converting enzyme activity (ACEA) in hypertension, the correlation between serum ACEA and the renin-angiotensin-aldosterone system was evaluated in hypertensive patients of whom 36 had essential hypertension, five had hypertension associated with chronic renal failure, three had renovascular hypertension, and one had primary aldosteronism. Serum ACEA was 17.0 +/- 3.3 U (mean +/- sd) in the normotensive control, 20.1 +/- 7.1 U in patients with essential hypertension, 11.6 +/- 3.4 U in patients with chronic renal failure, 31.7 +/- 1.1 U in patients with renovascular hypertension, and 9.7 U in primary aldosteronism in a recumbent state. There was a significant correlation between serum ACEA and plasma renin activity (PRA) (r = 0.615, p less than 0.001, n = 45) and plasma aldosterone concentration (PAC) (r = 0.599, p less than 0.001, n = 34) in a recumbent state. However, there was no significant correlation between serum ACEA and mean blood pressure. Serum ACEA elevated with furosemide and an upright posture significantly correlated with elevation in PRA (r = 0.369, p less than 0.05, n = 32) but did not significantly correlate with elevation in PAC. It is suggested, therefore, that the kidney is the suspected source of the plasma activity of the enzyme and that serum ACEA plays a possible role in the regulations of blood pressure and electrolyte metabolism modulating the renin-angiotensin-aldosterone system.