Angiotensin I converting enzyme activity in hypertension. Relationship to blood pressure, renin-sodium profiles, and antihypertensive therapy.

The activity of the angiotensin I converting enzyme was measured in 55 patients with untreated essential hypertension, 11 patients with untreated renovascular hypertension, five patients with untreated primary aldosteronism, and 23 normotensive subjects. Converting enzyme activity was significantly higher (p less than 0.025 or less) in essential hypertension (28 +/- 1 units/ml) and renovascular hypertension (28.5 +/- 3 units/ml) when compared with the activity in the normotensive subjects (21 +/- 1.5 units/ml). Seventeen (31 percent) of the patients with essential hypertension and three (27 percent) patients with renovascular hypertension had an elevated converting enzyme activity above the mean +2 standard deviations value of the normotensive subjects (32.8 units/ml), ranging from 33 to 55.8 units/ml. Converting enzyme activity was similar in black and white patients and in male and female patients, but it tended to decrease with increasing age in both the hypertensive and the normotensive subjects. In the untreated patients with essential hypertension (n = 55), converting enzyme activity was inversely related to mean arterial pressure and age (r = -0.34, p less than 0.01) and positively related to plasma renin activity (r = 0.31, p less than 0.05). Converting enzyme activity was always decreased during captopril therapy, and it was not affected by beta blockers, but it was increased by diuretics. These findings indicate that converting enzyme activity is elevated in patients with essential and renovascular hypertension.